This PDF file contains the front matter associated with SPIE Proceedings Volume 9255, including the Title Page, Copyright information, Table of Contents, Authors, Introduction, and Conference Committee listing.

The influence of temperature and incident pump power on reabsorption loss is theoretically discussed. Temperature characteristic and reabsorption loss rate of a diode-pumped quasi-three-level 946 nm Nd:YAG laser are investigated. Reabsorption effect has a significant impact on laser performance. The results indicate that reabsorption loss increases as the working temperature rises and decreases with the increased incident pump power.

A single-mode single frequency eye-safe pulsed all fiber laser based on master oscillator power amplification structure is presented. This laser is composed of a narrow linewidth distributed laser diode seed laser and two-stage cascade amplifiers. 0.8 m longitudinally gradient strained erbium/ytterbium co-doped polarization-maintaining fiber with a core diameter of 10 μm is used as the gain fiber and two acoustic-optics modulators are adopted to enhance pulse extinction ratio. A peak power of 160 W and a pulse width of 200 ns at 10 kHz repetition rate are achieved with transform-limited linewidth and diffraction-limited beam quality. This laser will be employed in a compact short range coherent Doppler wind lidar.

We report a linearly-polarized 1617 nm Er:YAG laser pumped by 1532 nm fiber-coupled laser diodes. An L-shaped resonator was employed incorporating two Er:YAG crystals which were pumped independently. In continuous-wave operation, a maximum output power of 7.73 W was obtained with an optical conversion efficiency of ~15.2% (versus incident pump power). To the best of our knowledge, this was the highest conversion efficiency ever demonstrated for a directly diode-pumped Er:YAG laser. In Q-switched operation, pulses with energy of 7.8 mJ and pulse duration of 80 ns were yielded at a repetition rate of 500 Hz, and the corresponding peak power was ~ 97 kW at 1617 nm.

FM-to-AM modulations are harmful to output characteristics of large-scale laser facility. In SG-III laser facility, some key techniques have been employed to suppress FM-to-AM modulations. Firstly, phase modulator was arranged at the end of fiber laser injection system to avoid GVD and PMD in the SM fiber system. Secondly, a fiber-based polarization rotated filter was proposed to suppress FM-to-AM modulations independently on each beam. Finally, less wave plates were employed and liquid crystal modulators were coated for decreasing weak etalon effect in preamplifier system. The results indicated that it can reduce the modulation depth less than 10% at a modulation frequency of 2.488GHz in SG-III laser facility.

The subject of the solid-state Raman frequency conversion to the yellow frequency spectra has been an active topic since the mid 1990’s, because of its application in bio-medical and astronomy fields. However, the yellow laser performance is often limited because of the cascade conversion to second or higher Stokes. This cascade conversion not only limits the conversion efficiency and the output power of the first Stokes, but also degrades the pulse and the beam profile of the first Stokes. We present a type of polarization coupled Raman resonator, in which the higher order ( the second Stokes and higher ) laser output can be dramatically suppressed. Our Raman resonator is pumped by a Q-switched and frequency doubled slab laser, and we can get an almost pure (P₅₅₉/(P₅₅₉ +P₅₃₂)>99%) 559 nm yellow light output with an efficiency over 39% from 532 nm to 559 nm. The resonator includes a high reflection rear mirror, a KGW crystal, a polarization coupled input/output element, and a high reflection output coupler of 559 nm (R_{559 nm} = 0.6). Furthermore, we have proposed an improvement of this polarization coupled Raman resonator. The theoretical calculations of the temporal and spatial dependent Raman conversion equations show that the conversion efficiency of the first order Stokes is greatly enhanced with an additionalλ/2 waveplate for 589 nm and the BBO crystal.

3~5μm mid-infrared laser has many important applications, such as gas detection, spectral analysis, remote sensing, medical treatment, and also in the military laser radar, infrared countermine, and so on. Optical parametric oscillator (OPO) is an efficient way to generate laser in this wavelength range, which has attracted the eyes of many people. In this paper, the recent development of mid-infrared OPO is overviewed. Meanwhile, detailed introduction on our recent work is given. Maximum idler output power of 34.2W at center wavelength of 3.35μm was obtained, to our knowledge, which is the new power record of the international public reporting for the continue-wave (CW) mid-infrared OPO. It is worth mentioning that the pump source, the quasi single-frequency (SF) narrow line width fiber laser, was also developed by our groups. According to the current status of research, some solutions is proposed in order to achieve higher power, narrower line width, and compact volume mid-infrared OPO in a wide tunable range.

A diode-pumped nanosecond Master Oscillator Power Amplifier (MOPA) system based on Nd:YLF crystal slabs has been demonstrated. The seed pulses with pulse duration of 11 ns were generated in an EO Q-switched Nd:YLF laser, with single pulse energy of 10 mJ. The 1047 nm signal pulses were amplified in a double-pass amplification system. Maximum output pulse energy of 270 mJ at a repetition rate of 50 Hz has been achieved with effective optical-to-optical efficiency of 14.5%.

A high-energy, high-beam-quality laser based on a single Nd:YAG rod with laser diode side-pumping and multiloop self-adaptive reciprocal cavity is presented. The optimized laser cavity geometry allowed to change the laser oscillation from single 200-ns self-Q-switched pulse followed by low-intensity free-running lasing to repetitive high-intensive pulses by periodically writing and erasing holographic gain gratings in the active Nd:YAG medium. The intensified self-Q-switching pulse train oscillation was realized by the interaction with a diffusely reflecting target placed in the focal plane of a lens at the laser output. Effects of shortening of the repetitive laser pulses down to 70-ns duration, stabilization of the pulse repetition period (~ 5 μs), and mode-locking temporal modulation of the pulses were observed. The use of a passive F2–:LiF Q-switch resulted in stable giant pulse train oscillation with total output energy of up to 0.43 J, individual pulse energy of 50 mJ, and its peak power of 4 MW at the individual pulse duration of 12 ns.

A laser-diode-pumped master oscillator and power amplifier was developed with high efficiency, high average power and high beam quality. The oscillator is an injection-seeding, fiber coupled diode-end-pumped E-O Q-switched Nd:YAG laser, producing single frequency pulse laser output with pulse energy of 8mJ and pulse width of 11ns at a pulse repetition rate of 1KHz，The 1KHz was divided into four chains with frequency of 250Hz, through E-O modulation technology, The power amplifier utilizes conductively-cooling Nd:YAG zigzag slab with two sides’ pump architecture at bounce point. Pulse energy of more than 800mJ with pulse widths of 12.6ns was obtained at repetition rate of 250Hz in every amplifier chain, the frequency-doubled pulse energy of 360mJ when KTP crystal was used was obtained at a repetition of 250Hz.

We report on the high power amplification of narrow-linewidth polarization-maintained (PM) laser in all-fiber PM MOPA configuration, which can operate with linewidth around 2GHz at above 1kW power level. Pump-limited maximum narrow-linewidth output power is 1.4kW without SBS effect, and the linearly-polarization single-mode output power was limited to ~550W by mode instabilities (MI). The beam quality of the fiber amplifier (M² ) was measured under different power, which degrades gradually from ~1.4 to ~2.2 after the onset of MI. The polarization extinction rate is measured to be about 90% before the onset of MI and reduce dramatically after MI sets in. The experimental results are analyzed based on a novel semi-analytical model, which has taken the effects of gain saturation into account. The theoretical results agree well with the experimental results. Mitigating MI by coiling the gain fiber has been analyzed and demonstrated numerically. It shows that, by tight coiling of the gain fiber to a radius of 4cm, the MI threshold can increase to 2.5 times higher than that without coiling or loose coiling, which means that the amplifier have the potential to achieve MI-free 1.4kW output power.

The thermal effects of a liquid direct cooled split disk laser are modeled and analytically solved. The analytical solutions with the consideration of longitudinal cooling liquid temperature rise have been given to describe the temperature distribution in the split disk and cooling liquid based on the hydrodynamics and heat transfer. The influence of cooling liquid, liquid flowing velocity, thickness of cooling channel and of disk gain medium can also be got from the analytical solutions.

A compact diode side-pumped conductively cooled 1047 nm Nd:YLF slab laser with high energy and short pulse width is developed. Through ray tracing method, we design a home-made pump module to homogenize the pump intensity. Based on the Possion equation, a thermal conduct model of side-pump laser is established. The temperature distribution in laser crystal is obtained, and the thermal lens is caculated. With the absorbed pump energy of 818 mJ, the maximum output energy of 228 mJ is achieved in free-running mode. At a repetition rate of 50 Hz, 160 mJ, 9 ns 1047 nm infrared light is obtained under the maximum absorbed pump energy, and the slope efficiency is 27.8%.

To assure that the frequency conversion crystals of SG facility are always being in the best shot position, and have the highest energy conversion efficiency with various beam conducting directions, we researched the precise tuning technique of frequency conversion crystals with the SG facility. The on-line quick tuning method of target point detecting with preshot was used in precise tuning of crystal match angle, and helped to correct the off-line match angle satisfactorily. With crystal alignment technique and crystal accompany technique, the precise tuning of crystal match angle can assure the crystals to maintain a stable high efficiency in a long experiment period.

In this paper, the operation properties of unstable resonators with graded reflectivity mirror (GRM-UR) are studied numerically in a solid-state thin-disk laser in terms of beam quality and power threshold. By comparing to traditional unstable resonator with same output coupling fraction, results show that the GRM-UR is advantageous to suppress ASE effect, but hard to achieve better beam quality when the phase aberrations cannot be well compensated within the cavity.

Large-aperture electro-optical switch based on plasma Pockels cell (PPC) is one of important components for inertial confinement fusion (ICF) laser facility. We have demonstrated a single-pulse driven 4×1 PPC with 400mm×400mm aperture for SGIII laser facility. And four 2×1 PPCs modules with 350mm×350mm aperture have been operated in SGII update laser facility. It is different to the PPC of NIF and LMJ for its simple operation to perform Pockels effect. With optimized operation parameters, the PPCs meet the SGII-U laser requirement of four-pass amplification control. Only driven by one high voltage pulser, the simplified PPC system would be provided with less associated diagnostics, and higher reliability. To farther reduce the insert loss of the PPC, research on the large-aperture PPC based on DKDP crystal driven by one pulse is developed. And several single-pulse driven PPCs with 80mm×80mm DKDP crystal have been manufactured and operated in laser facilities.

The quality of clamping device for PPMgLN crystal has a vital influence on the optical property of solid-state laser. It has highly requirements of work stability and environmental adaptation ability, especially the thermal adaptation under high temperature differences. To achieve thermal adaptation, structural stiffness will be unavoidably weakened. How to keep both enough stiffness and thermal adaptation as far as possible is the key design point and also difficult point. In this paper, a kind of flexible thermal release unit which can work permanent under 130±10°C is studied. Thermal compensation principle and flexible thermal release theory are applied. Analysis results indicate that this device can effectively decreased the thermal stress of the crystal from 85MPa to 0.66MPa. The results of the vibration resistance test on the optical axis direction of the crystal indicate that the device can provide at least 5.62N to resistant 57.2g impact vibration and 18.5g impact vibration in the side direction, well satisfied the requirements of ability to resistant 6g impact vibration.

Tapering will raise the signal loss in an end-pumped (N+1)×1 type combiner. In this paper, the Thermally Expanded Core (TEC) technique is used in the signal loss optimization experiment with the tapering ratio of the pump combiner is 0.6. The experimental results indicate that the coupling efficiency of the 1.55μm signal light increases from 81.1% to 86.6%, after being heated 10 minutes at the homo-waist region of the tapered signal fiber with an 8mm wide hydroxygen flame. Detail analysis shows that the TEC technique can both reduce the loss of the LP01 mode and the LP11 mode in the signal fiber.

XG-III laser facility is a petawatt laser which has a unique feature of three synchronized pulses output for various pump-probe experiments. To realize the synchronization with zero timing jitter, we have designed and implemented a novel front-end system based on super-continuum injected femtosecond optical parametric amplification (fs:OPA). Critical parameters of fs:OPA were optimized for the best conversion efficiency. Experimental results verified that major design specifications such as pulse energy, central wavelength and spectral width were fully accomplished and a high pulse contrast ratio was also achieved by the fs:OPA process.

The effect of the gain fiber parameters for the design of a short wavelength ytterbium doped fiber laser (YDFL) is analyzed theoretically, and based on these analyses, we find viable approaches to improve the laser performances. High power 1018 nm YDFL system was constructed, output characteristics of 1018 nm laser with the core/cladding, doping concentration and gain fiber length are experimentally investigated. It is found that increasing the core/cladding area ratio, reducing the doping concentration and shortening the fiber length is effective way to suppress the amplified spontaneous emission (ASE) gain and ensure the laser operation at 1018 nm. A record output power of 154 W at 1018 nm is obtained, with a brightness of 5.7GW/cm² -sr, optical-optical conversion efficiency is 71% when the laser operated at maximal power. Meanwhile, ASE and spurious oscillation are suppressed efficiently.

An end-pumped laser amplifier with high efficiency and compactness was designed. The thermal stress of symmetrical single-cladding and double-cladding planar waveguide with Nd:YAG as its core were analyzed theoretically, and the maximum thermal load for each were also obtained according to the stress fracture limit. For different inner cladding thickness, the maximum pump power that could be absorbed was calculated. The laser medium was chosen to be a symmetrical double-cladding planar waveguide with Nd:YAG as its core, the dimensions of the gain area were 50mm×12mm×100μm, and the waveguide were 60mm×12mm×2mm. The single thickness of inner cladding YAG and the outer cladding sapphire were 250μm and 700μm respectively. The size of LDA pump light was 18.9mm and 10mm respectively in fast axis and slow axis. The seeder was coupled into the waveguide from one end, and the outer cladding were welded with two heat sink for heat transfer. By theoretical calculation, if the seeder into the waveguide is 0.1W, the outputting power of 1651W could be obtained when the pump power from the LD array was 3600W, with the optical-optical efficiency of 46%.

In order to ensure the high power all-fiber laser reliability and excellent beam quality, it is necessary to strip the unwanted cladding light. The common method for stripping cladding light is to recoat the double cladding fiber with a high index gel, but localized heating and low thermal conductivity of the recoating gel are the prime factors limiting the power-handling capability of the cladding power stripper(CPS). An improved fabrication technique to manufacture the CPS is presented. Light stripping section of the fiber is fused with a transparent quartz tube, by applying different amount of etchant along the quartz tube, frosted surface is created and uniformly removal of the cladding light is achieved. The quartz tube is joined to water-cooled thermal enclosure tightly without the gel to avoid heat aggregation. The power-handling capability of the device is tested under 200W of cladding light, and attenuation of 20 dB is achieved.

The thermal problems of CPS and YDF were studied. And the thermal management technologies are developed separately to the problems. Experimental results showed that the thermal management technologies worked well.

The side-coupled cladding-pumped fiber has many advantages in terms of system design, ease of pump injection, signal extraction and power scalability over traditional double cladding fiber. We demonstrate a 290-W all home-made side-coupled cladding-pumped fiber laser with the slope efficiency of 67.8%. To the best of our knowledge, the slope efficiency is the highest for the published high power fiber laser based on the DSCCP fiber. The slope efficiency of the home-made side-coupled cladding-pumped fiber amplifier is mainly limited by the background loss, pump light coupling and pump light absorption. The results show that the power ratio of signal light to residual pump light is near 20 dB. The pump light is not absorbed enough that the slope efficiency can be further improved by optimizing the amplifier structure.

An introduction was given to the active segmented mirror(ASM) used in coherent beam combination firstly. Based on the actuator distribution of ASM, the computational formula between the perturbation voltage of each actuator and the perturbation of piston or tip/tilt was acquired. Then the numerical analysis of correction process with two different perturbation ways in SPGD algorithm was carried on. By comparing the two correction processes, it was found that the convergence speed of the second method is 25 times as fast as the first one when there only existed piston error between the two beamlets, while the convergence speed was almost the same when there only existed tip/tilt error, and the convergence speed is 5 times when there existed both piston and tip/tilt error.

For powers exceeding a threshold the spectral broadening in fiber amplifiers becomes a significant challenge for the development of high power narrow bandwidth fiber lasers. In this letter, we show that the spectral broadening can be partly caused by four-wave mixing(FWM) process in which the power of the central wavelength would transfer to the side ones. A practical FWM induced spectral broadening theory has been derived from the early works. A numerical model of fiber amplifier has been established and FWM process has been added to the model. During the simulation process, we find that when a 10 GHz, several watts narrow bandwidth laser is seeded into a few modes fiber laser amplifier, the FWM induced spectral broadening effect might continually increase the FWHM of the spectra of the continuum laser to 100 GHz within the amplification process to several hundred watts which has been convinced by our experiments. Some other results have also been analyzed in this paper to complete the four-wave mixing induced spectral broadening theory in fiber amplifiers.

In this paper, based on the self-reproduction condition of laser wavefront curvature, the influences of disk defocus on laser parameters can be calculated. The laser-pumping overlapping efficiency will decrease by 9%; the magnification will rise to 2.3, and the intra-cavity loss will be high to 30% due to a laser beam size mismatch when each disk has focal length of -100 m in a positive-branch confocal unstable resonator containing four disks with magnification of 1.8. Therefore, the optical conversion efficiency and stability will be reduced significantly. Several methods defocus compensation of are compared, it can be found that inserting variable-focus lens in resonant is useful in large dynamic range. In experiment, the defocus values are measured in different pumping power. A lens group, used for compensate components according to the single pass probe, is carefully designed. Under this compensation, the pulse energy can be maintained in 10 J from 1 Hz to 100 Hz. The output power can be improved 2.33 times compared to non-compensation condition.

In this paper we investigate the effects of cooling water temperature and pumping diode laser beam profile on the disk laser beam quality. The results show that both issues are important and can influence the beam quality but at the conditions of our experiment these issues do not affect the beam quality significantly.

A Nd:YAG thin disk is end-pumped by two high power laser diodes and the fluid flows in a narrow channel to cool it directly. The forced convection occurs between the fluid and disk. A system is designed to measure the convective heat transfer coefficient with different flow rate. With the measured coefficient, the temperature and thermal stress in the disk are numerically analyzed. The maximum permissible thermal load is calculated, which increases with the increasing flow rate. Furthermore, the optical path different distribution is numerically calculated by considering of the thermo-optical effect, and thermal expansion at the maximum permissible thermal load. These results are useful for design of a direct-liquid-cooled Nd:YAG thin disk laser.

Lasers in the eye-safe 2 μm spectral region are attracting significant interest due to a variety of applications such as atmospheric lidar sensing and medical treatment, which require laser sources matching the absorption lines of various molecules in the 2 μm wavelength region. We demonstrate an all-fiber Tm/Ho-codoped laser operating in the 2 μm wavelength region with a wide wavelength tuning range of more than 300 nm. The Tm/Ho-codoped fiber laser (THFL) was built in a ring cavity configuration with a fiberized grating-based tunable filter to select the operating wavelength. The tunable wavelength range of the THFL was from 1727 nm to 2030 nm. To the best of our knowledge, this is the widest tuning range that has been reported for an all-fiber rare-earth-doped laser to date. Efficient short wavelength operation was also achieved. The output power of the THFL was further scaled up from 1810 nm to 2010 nm by using a stage of Tm/Ho-codoped fiber amplifier (THFA), which exhibited the maximum slope efficiency of 42.6% with output power of 408 mW at 1910 nm.

An overview of Czech national R&D project HiLASE (High average power pulsed LASEr) is presented. The HiLASE project aims at development of pulsed DPSSL for hi-tech industrial applications. HiLASE will be a user oriented facility with several laser systems with output parameters ranging from a few picosecond pulses with energy of 5 mJ to 0.5 J and repetition rate of 1-100 kHz (based on thin disk technology) to systems with 100 J output energy in nanosecond pulses with repetition rate of 10 Hz (based on multi-slab technology).

With the improvement of output power, efficiency and reliability, high power semiconductor lasers have been applied in more and more fields. In this paper, a conduction-cooled, high peak output power semiconductor laser array was studied and developed. The structure and operation parameters of G-Stack semiconductor laser array were designed and optimized using finite element method (FEM). A Quasi-continuous-wave (QCW) conduction-cooled G-Stack semiconductor laser array with a narrow spectrum width was fabricated successfully.

High power diode lasers have been widely used in many fields. For many applications, a diode laser needs to be robust under on-off power-cycling as well as environmental thermal cycling conditions. To meet the requirements, the conduction cooled single bar CS-packaged diode laser arrays must have high durability to withstand thermal fatigue and long lifetime. In this paper, a complete indium-free bonding technology is presented for packaging high power diode laser arrays. Numerical simulations on the thermal behavior of CS-packaged diode laser array with different packaging structure were conducted and analyzed. Based on the simulation results, the device structure and packaging process of complete indium-free CS-packaged diode laser array were optimized. A series of high power hard solder CS (HCS) diode laser arrays were fabricated and characterized. Under the harsh working condition of 90s on and 30s off, good lifetime was demonstrated on 825nm 60W single bar CS-packaged diode laser with a lifetime test of more than 6100hours achieved so far with less 5% power degradation and less 1.5nm wavelength shift. Additionally, the measurement results indicated that the lower smile of complete indium-free CS-packaged diode laser arrays were achieved by advanced packaging process.

High-power laser bars and single emitters have proven as attractive light sources for many industrial applications such as direct material processing or as pump sources for solid state and fiber-lasers. There is also a great interest in quasi-CW laser bars for high-energy projects. These applications require a continuous improvement of laser diodes for reliable optical output powers, high electrical-to-optical efficiencies, brightness and costs. In this paper JENOPTIK presents an overview of recent research for highly efficient CW and quasi-CW laser devices emitting in a wide wavelength range between 880 nm and 1020 nm. The last research results concern the 9xx single emitters and laser arrays. The 9xx nm 12 W single emitters and 976 nm 55 W laser arrays have efficiencies above 65%. New life time tests for single emitter devices currently exceed 1300 hours of reliable operation at room temperature and over 1500 hours at 45°C. Because of the small far field distribution of the optical power, the high output power and the small near field the 55 W arrays show a brightness of 75 MW x cm^-2sr^-1 with 95% power content. The technology for new generation 940 nm high fill-factor bars has been currently extended to emission wavelengths of 976 nm and 1020 nm with excellent results: 200 W output power with 63% efficiency using passive cooling. The innovative design of the laser structure enables, moreover, the realization of 500 W 880 nm quasi-CW laser bars with wall-plug efficiencies of 55% and a narrow fast-axis divergence angle of 40° (95% power content).

Diode-pumped solid state laser system based on cryogenic Yb:YAG active-mirror scheme are presented with recent energy output. With improved optical design, 6.05J/1Hz pulse energy is achieved and a conceptual design with 30J output energy is theoretical simulated. The doubling efficiency of YCa⁴O (BO³)(YCOB) crystal is also discussed in this paper.

The paper presents the technical design and progress on a special high-power laser facility, i.e. XG-III, which is being used for high-field physics research and fast ignition research. The laser facility outputs synchronized nanosecond, picosecond and femtosecond beams with three wavelengths, i.e. 527 nm, 1053 nm and 800 nm respectively, and multiple combinations of the beams can be used for physics experiments. The commissioning of the laser facility was completed by the end of 2013. The measurement results show that the main parameters of the three beams are equal to or greater than the designed ones.

Backward Raman amplification (BRA) in plasma has been demonstrated an effective way to produce high power laser pulses. However, most experiments of BRA are carried out around the pump wavelength of 800 nm. In recent years, the 1053 nm pump pulse becomes more and more essential as the development of the chirped pulse amplification (CPA) around this wavelength. Here we design an experiment of BRA with a 1053 nm, 20 ps pump pulse and a 1200 nm, 50 fs seed pulse based on the facility of XG III. The simulation results obtained by a 1-d particle-in-cell (PIC) code show that the amplified peak seed intensity of ∼ 5 × 10¹⁶ W/cm² is obtained, with an energy transfer up to 16.8%. An output pulse of petawatt power is theoretically demonstrated feasible.

A high average-power all-fiber supercontinuum laser source is constructed. By integrating series techniques together, the output average power achieves 65W with the spectrum range covering two octaves from 540nm to 2200nm. To our knowledge, there has been never reported similar supercontinuum source with such high average power, broadband spectrum and picosecond pulse width.

A spectral shaping method during the optical parametric chirped pulse amplification is presented. The relationship between the temporal shape of the signal pulse and the pump pulse is analyzed theoretically, which shows that the temporal shape of the signal pulse can be modulated through modulation of the pump pulse. This is proven by our verification experiment. And we have successfully used this method in the pre-amplifier of the XG-III laser facility to modulate the signal spectrum to match the requirements of the main amplifier.

Meter-sized gratings are urgently required by ultra-short ultra-high lasers, especially petawatt and multi-petawatt lasers, in the world wide. Object-image-grating self-tiling method gives a way to achieve an ideal grating tiling condition by completely eliminating three tiling errors within a traditional tiled grating. However, some application problems challenges it actual application in laser systems. In this paper, we will discuss the influence of two important problems: the stability problem and the spectrum amplitude modulation problem. And related simulations and analyses are developed to promote the application of this method in large-scaled lasers systems.

In a high-energy chirped-pulse-amplified laser system, grating tiling technology provides an effective means to increase the aperture of the gratings and to scale the energy and irradiance of short-pulse lasers. The difficulties lie in controlling tiling errors accurately between the sub-gratings and keeping long time stability. In this paper, a two-pass full-tiled grating-compressor (TGC) with real- time control unit is developed for the first time. The far-field distributions of the 0^th order and -1 ^st order diffracted beams of the two pairs of tiled gratings are monitored by the same CCD system, with the main laser chain being not disturbed. In this way, we realize online real-time control of tiling errors. Through a method of locking the far-field image to compensating the temporal drift, we can realize the automation of the assembly. The TGC has successfully applied in the multi-function XGIII laser facility, and focusing focal spot and output pulse width are obtained.

Chirp pulse amplification (CPA) has been promoted as an effective way to explore the intensity frontier. High order dispersion induced by the stretcher and materials in the CPA system, which deteriorates both the pulse duration and temporal contrast, however, can not be absolutely compensated by the compressor. Placed at the Fourier plane of a 4f zero-dispersion stretcher consisting of a grating, the deformable mirror (DM) has been demonstrated as the modulator to compensate high order dispersion. Using the method of ray tracing, the relation between spectrum and position on DM has been obtained. It shows that the resolution of the deformable mirror can be controlled by adjusting the focal length and incident angle. We have simulated a typical Ti:sappire CPA system to revise the spectral phase by the DM. The result illustrates that if the spectral phase can be compensated, the temporal contrast will be improved by 2 order of magnitude.

Array element tiling is one of the key technologies for the coherent beam combination in a high-power laser facility. In this paper, we proposed a method of the array element auto-tiling based on capacitive displacement sensor. The method was verified on a double-pass tiled-grating compressor in XG-III laser facility. The research showed that the method is an effective way to control the misalignment errors automatically, with high precision and long-term stability.

The singular point of the dissipative soliton mode-locked fiber laser is demonstrated experimentally. Mode-locked pulses are severely disturbed under certain pump power. The peak-valley (P-V) of the output power reaches up to 26.5% under the pump power of 918mW. However, mode-locked fiber laser can operate stably under higher or lower pump power. A numerical model based on nonlinear Schrödinger equation (NLSE) is established. And the singular point of the mode-locked state is theoretically proved.

With a recent developed mode-coupling model, the Brillouin gain spectra (BGS) of multi-mode fibers (MMF) are investigated and compared with the corresponding experiment. It is found that the calculation results are coincident well with the experiment data. Furthermore, the BGS are found to be very sensitive to the index fluctuation. Such phenomenon is demonstrated by introducing a small index hump or dip in the center of the fiber core. And it can be explained by that the index fluctuation may influence the acoustic mode greatly.

A eigenmode expansion method (EME) is proposed to solve the laser eigenmode of optical resonator with intra-cavity phase aberration (ICPA) semi-analytically. In this model, the eigen-equation of OR, so called self-reappearance condition is translated to be a linear eigen-value problem, and it is proved that all eigen-modes can be obtained for any resonators. The linear eigen-value problem is solved numerically, and it gives out the transverse distribution and corresponding eigen-value of each eigenmode, which describe the light field and diffraction loss, respectively. Compared with traditional methods, EME is a semi-analytical method which is unlimited by the order of phase aberration, and it can be solved without numerical iteration. The existing of local modes (LM) in OR with ICPA is proved with EME, which may be the source of local damage on solid medium. And the use of output coupler with transmission, such as graded reflectivity mirror (GRM), can prevent the appearance of LM and improve beam quality. Specially, for the ICPA coupled with laser extraction, the linear eigen-value equations become a nonlinear problem, which are numerically solved by the finite-difference Jacobian method. The result shows that the optical resonator exhibits transverse modal instability (TMI) with certain cavity parameters.

We study the mode evolution properties in a 3 x 1 adiabatic tapered single-mode fiber combiner (ATSMFC) in theory. The fabrication of the combiner for single mode fibers based on adiabatic tapered fused bundle (TFB) technique with the assistant of low index glass capillary is introduced. The whole taper region can be seen as three phase: single-mode fibers, multi-core fiber and multi-mode fiber. Supermodes of three-core fiber with scalar mode results are derived based on coupling mode theory. The analysis is verified with numerical examples by fully vectorial finite element mode solver (Cosmol Multiphysics). Simulation results show that the three input core modes in single-mode fibers gradually evolve into three supermodes in three-core fiber and then evolve into three low-order modes in the multi-core fiber. Effective indices for different modes are calculated which can depict the evolution process vividly. The results may be useful for practical high power fiber laser systems.

HfO₂/SiO₂ high reflective optical coatings are widely used in high power laser applications because of their high laser damage resistance and appropriate spectral performance. The residual stresses strongly influence the performance and longevity of the optical coatings. Thermal stresses are the primary components of the residual stresses. In the present work, the distribution of thermal stresses in HfO₂/SiO₂ high reflective optical coatings was investigated using two different computational methods: finite element method (FEM) and an analytical method based on force and moment balances and classical beam bending theory. The results by these two methods were compared and found to be in agreement with each other, demonstrating that these two methods are effective and accurate ways to predict the thermal stresses in HfO₂/SiO₂ optical coatings. In addition, these two methods were also used to obtain the thermal stresses in HfO₂/SiO₂ optical coatings with different layer number to investigate the effect of the layer number on the thermal stresses of the HfO₂/SiO₂ optical coatings. The results show that with the increase of the layer number, the stresses in the substrate increase, while the stresses in the respective SiO₂ and HfO₂ layers decrease. Besides, it was also found that the radius of curvature of the coating system decreases as the layer number increases, leading to larger bending curvature in the system.

In order to resolve the disadvantages such as poor appearance quality, poor tightness, low efficiency of resistance spot welding of stainless steel rail vehicles, partial penetration lap laser welding process was investigated widely. But due to the limitation of processing technology, there will be local incomplete fusion in the lap laser welding seam. Defect rate is the ratio of the local incomplete fusion length to the weld seam length. The tensile shear strength under different defect rate and its effect on the car body static strength are not clear. It is necessary to find the biggest defect rate by numerical analysis of effects of different defect rates on the laser welding stainless steel rail vehicle body structure strength ,and tests of laser welding shear tensile strength.

The Power Spectral Density (PSD) is the specification of mid-spatial-frequency phase error in high power solid-state laser facilities. Its evolution during propagation and connection with laser performance have not been fully discussed due to the complexity of nonlinear propagation. We present in this paper the analytic forms of PSD of output phase and intensity modulation, which could be obtained from the input phase PSD introduced by imperfect optics. Moreover, we connect the PSD with the important laser performance parameters: the relative intensity of wings on the focal spot and the contrast ratio of the near-field.

Physical model was established to describe the pulse superposition in multi-pass amplification process when the pulse reflected from the cavity mirror and the front and the end of the pulse encountered. Theoretical analysis indicates that pulse superposition will consume more inversion population than that consumed without superposition. The standing wave field will be formed when the front and the end of the pulse is coherent overlapped. The inversion population density is spatial hole-burning by the standing wave field. The pulse gain and pulse are affected by superposition. Based on this physical model, three conditions, without superposition, coherent superposition and incoherent superposition were compared. This study will give instructions for high power solid laser design.

The new simulation code of high power discharge has successfully developed. The code is not executed by mainframe computer, PC, nor Macintosh, but by iPhones. The details, such as development environment and process are described in this paper below.

This paper presents the key issues for high precision pointing system using Risley prism. An iterative optimization algorithm is proposed to solve the inverse problem of Risley Prism and anti-achromatic Risley Prism. Different error sources, particularly Risley prism's rotation errors and rotation axis jitters are considered. Error propagation formula between pointing accuracy and rotation position is deduced. Finally, a beam steering simulation system including target position creating module, Risley Prism inverse solution module, Risley Prism rotation control module and beam pointing module is established. The simulation results show that it can achieve better than 1 arcsec pointing accuracy.

In this paper, a numerical model is presented to simulation the performance of the wavelength-beam-combined laser diode arrays (LDA) system. The eigen mode expansion method is used to describe the two-dimensional optical amplification and the strength of field feedback of external cavity. To describe the mode competition in laser diodes, the gain saturation effect is considered. The two-dimension distributions of the carrier concentration, recombination rates, and optical gain are calculated for solving the laser dynamic equation. The Fresnel integration, grating equation and mode overlap integration are used to obtain the feedback coefficient of extent cavity diffraction. Quantum noise is considered to evaluate the spectral linewidth of semiconductor laser. Based on the numerical model, the impact of the mutual optical feedback on the beam quality and spectrum of the LDA is present and analysis.

A novel conception of iterative pump number was introduced in this work for the first time. Based on the conservation of energy, the equivalent model for the lasering of solid state laser was built up, the iterative pump number was calculated, and a formula for the output power of laser was given. This formula presented the relationships among the output power of laser, pumping power of diode and the thickness of laser medium. The output power predicted by this formula is consistent with experimental results, so this formula could be an important tool for the designing of parameter for diode pumped solid state laser.

Because of low frequency distorted wave front impacting on beam quality in ICF system, a thin mirror with diameter 300mm is optimized in order to compensate the distorted wave front. Meanwhile, the influences of low frequency distorted wave front made to laser beam quality are discussed in detail. Far field beam quality before and after compensating distorted wave front is discussed in detail, too. The analysis results show whether the space scale parameter of the low frequency wave front is altered or the amplitude of the wave front is changed, the amplitude of the wave front decrease obviously, phase gradient reduce during the whole spatial period, the peak of far field intensity increase, power focusability of focal spot is improved obviously.

EasyLaser is component-based laser system simulation software. Beam control system simulation is a main part of EasyLaser, which can be used for systems with multi-optical paths, multi-wavelength beams, and multi-controllers. A new numerical method about general kinematics separation is proposed for beam control system simulation. It provides axis rotation conversion relationships due to orientation data of apparatus of system, such as gimal, sensor and optical mirror. It gives their coupling and uncoupling matrixes in kinematics and controller model. The matrixes could change every iterative time automatically during the dynamic tracking process. The main advantage of the method is more suitable to solve the problems that the gimbal movement and geometry optical transmission are considered simultaneously. By using the method, sensor images and undershoot data are updated automatically. And further the kinematic driver or controller signals are separated automatically. Therefore the tracking and beam control can be designed without consideration of the system kinematical composition. Then the beam control system simulation has the virtues of generality, flexibility, and usability. No matter what kinds of gimbal and optical path, designer needs only to consider tracking and beam control aspects. In addition, a union beam control example for atmosphere transmission correction is given. It includes tracking tilt mirror and adaptive optics system. Simulation results show that the low-frequency fluctuation is restrained effectively and the high-frequency fluctuation is corrected obviously.

When chemical oxygen-iodine laser (COIL) runs longtime, the influence on heating effects of mirrors has attracted attention abroad. For obtaining accurate estimate on it, relying on past experience, we carry on coupling simulation among flow field, optical field and heating effects of mirrors. At present computational condition, three-dimensional model about nozzle flow is constructed; by analyzing simulation data, coupling simulation result is obtained between flow field and optical field. Finally, the influence on heating effects of mirrors is investigated. The focus is solving the convergence of iteration between flow field and optical field. By particular analysis on the physical mechanism, coupling style is adjusted; finally, stable result is obtained, coupling iteration times is reduced greatly. The simulation result indicate if considering actual flow field disturbance, facular fragmentation is distinct; the disturbance exist from the beginning, so it influences on beam quality in the whole course.

Modeling of Tm-doped fiber lasers pumped with 793 nm, 1.6 μm and 1.9 μm is presented and compared. Output performance of three different pump schemes with active fiber length, pump power and output reflectivity is investigated. Numerical simulation shows that, with 793 nm pump, the cross relaxation process is of vital importance for high efficient operation of Tm-doped fiber laser. And, 1.9 μm pump scheme is more likely to offer even higher output compared with 793 nm pump and 1.6 μm pump.

Amplified spontaneous emission (ASE) causes the decrease of the inverted population density and the nonuniformity of gain in slab amplifier for high power laser systems. In this paper, a three dimension model, based on the data in SG-II, in which the residual reflection in the cladding and the ASE process are taken into consideration, is built to analyze the space distribution and time evolution of small signal gain coefficient using Monte Carlo algorithm and ray tracing. This model has been verified by comparing with the experimental data. The traverse size of slab is 68.2cm×36.3cm, which is usually decided by the clear aperture and the manufacture. By means of the model, the impact of thickness, residual reflectivity and the stimulated cross section of neodymium glass to the ASE are analyzed in detail.

Diode-pumped alkali lasers (DPALs) have attracted a lot of interests in the recent years because of their high Stokes efficiency, good beam quality, compact size, and near-infrared emission wavelengths. Until now, the thermal features have been only analyzed in an open alkali cell. In this report, we established a mathematical model to examine the heating effect of a static sealed rubidium cell by means of a Finite Difference (FD) procedure. After assuming the absorption coefficient of the alkali vapor, the temperature distributions of a real sealed rubidium vapor cell have been acquired for different powers and beam waists of the pump. The analytic conclusions would be helpful in designing a feasible DPAL.

Experimental research on non-critical phase-matching fourth harmonic generation with ADP and DKDP crystals are reported. The characteristics of 2ω-to-4ω efficiency as function of incident angle, crystal temperature and input 2ω intensity have been investigated in detail, and the 2ω-to-4ω conversion efficiency has been demonstrated up to 84.1% with ADP crystal and 85.1% with DKDP crystal, respectively. Nevertheless, the spatial non-uniformity of rapid grown DKDP crystal has to be improved while the temperature control uniformity should be upgraded for ADP crystal to realize large aperture high efficiency fourth harmonic generation.

Activities on diode pumped alkali laser (DPAL) in Japan is reviewed. We have started alkali laser works in 2011, and currently, we are the only players in Japan. Our interests are application oriented, and it is not only defense but also industrial. DPAL is a good candidate as a source of remote laser machining, thanks to its scalability and extremely good beam quality. We are studying on scientific and engineering problems of Cs DPAL with a small-scale apparatus. A commercial diode laser with volume Bragg grating outcoupler is used to pump the gain cell longitudinally. A 6.5 W continuous-wave output with optical to optical efficiency of 56% (based on the absorbed power) has been achieved. Numerical simulation codes are developed to understand the physics of DPAL and to help future developments.

The development of a discharge oxygen iodine laser (DOIL) requires efficient production of singlet delta oxygen O₂(α¹ Δ) in electric discharge. It is important to understand the mechanisms of of O₂α¹ Δ) quenching in these devices. To gain understanding of this mechanisms quenching of O₂(α^]1 Δ)in O/O₂/O₃/CO₂/He mixtures has been investigated. Oxygen atoms and singlet oxygen molecules were produced by the 248 nm laser photolysis of ozone. The kinetics of O₂(α¹ Δ) quenching were followed by observing the 1268 nm fluorescence of O₂α¹ Δ → X³ Σ transition. It is shown that vibrationally excited ozone O₃(υ;) formed in the three-body recombination O + O₂ + M →O₃(υ) + M is an important O/O₂/O₃ quenching agent in O/O₂/O₃ systems. The process O₃(υ ≥2) + O₂(a¹ Δ)→ 2O₂ + O is the main O₂(α¹ Δ) deactivation channel in the post-discharge zone. If no measures are taken to decrease oxygen atom concentration, the contribution of this process into overall O₂(α¹Δ) removal is significant even in the discharge zone. It was found in experiment that addition of species that are good quenchers of O₃(υ;) decrease O₂(a¹ Δ) deactivation rate in the O/O₂/O₃ mixtures.

Due to the existence of various disturbances during the lasing process of the chemical oxygen iodine laser (COIL), the optical beam pointing performance is severely degraded. In this paper, an adaptive control methodology is proposed for the precise pointing control of the optical beam with active beam jitter rejection using a giant magnetostrictive optical deflector (GMOD) which exhibits severe dynamic hysteresis nonlinearity. In particular, a least square support vector machine (LS-SVM) based fast compensator is employed to eliminate the dynamic hysteresis without the inverse model construction. Then an improved feedforward adaptive filter is developed to deal with jitter attenuation when the full-coherent reference signal is unavailable. To improve the stability and overall robustness of the controller, especially when a large initial bias exists, a PI controller is placed in parallel with the adaptive filter. Experimental results validate the precise pointing ability of the proposed control method.

¹ Δ_g oxygen was the active medium of chemical oxygen iodine laser (COIL), the concentration and distribution of ¹ Δ_g oxygen was important for the output power and beam quality. However, the current test technique, such as fluorescence detection method, absorption spectrum method could not get accurate ¹ Δ_g oxygen information, due to the interference from the iodine fluorescence or the rigorous request of the laser source and optics and detection elements. The anti-stokes Raman spectrum of ¹ Δ_g oxygen was regarded as a potential technique to obtain desirable signal, and the coherent anti-stokes Raman scatter (CARS) was the most feasible technique to get better signal to noise ratio (SNR). In this paper, we reported a broadband nanosecond coherent anti-stokes Raman scatter (CARS) detecting system built up for the detection of the concentration and distribution of O₂( ¹ Δ_g) in COIL：The second harmonic of a Nd: YAG pulse laser was separated into two parts, one part was used to pump a broadband nanosecond dye laser to generate light of 578-580 nm, which covered both stokes lines of O₂ ( ¹ Δ_g）and O₂ (³ ∑）; The other part was combined with dye laser output by a dichroic mirror, and then introduced into the detection region of COIL through a focus lens. CARS signals for O₂（¹ Δ_g）and O₂ （³ ∑）have different wavelengths, and their intensity was proportional to the square of the concentration of O₂（¹ Δ_g） and O₂( ³ ∑). By changing the focus spot of pump and stokes laser, the concentration distribution of O₂（¹ Δ_g） and O₂（³ ∑）at different position could be obtained.

Kilowatts class diode-pumped Cs vapor laser (DPCL) has been realized and this kind of lasers have military applications potentially for its high output power with high efficiency. Pumped by a fiber coupled laser diode, the key operating parameters of a DPCL are studied, including the spot size of focused pumping light, pressure ratio of buffer gases, vapor cell length, temperature of Cs vapor and reflectivity of output coupler. The spot size is properly chosen in the consideration of both the intensity scalability and mode matching. Pressure ratio is optimized under a modest pressure of mixed gases of helium and ethane. Under the optimized pressure ratio, the Cs vapor can absorb the pumping energy and convert it into laser energy efficiently. Besides, the temperature and reflectivity are also optimized to operate the DPCL in optimum state. The results have significant instructions for the experimental design of DPCL.

Alkali laser has been one of the most promising paths to high energy laser during past dozen years. As the first group realized DPAL and XPAL lasing in China, we had done lots of theoretical and experimental works to further clarify the mechanism of alkali lasers, such as exploring scaling parameters design balance and MOPA configuration amplified spontaneous emission suppression in DPAL based on our self-developed fast converging algorithm, XPAL’s continuous wave operation threshold, performance degradation of VBG narrowed diode laser array and stacks due to conductive thermal flow, heat deposition induced gas dynamic parameters variation estimation, local atomic number density change measurement with single frequency tunable diode laser, ionization and other higher level nonlinear effects with opto-galvanometer method. Based on above research works, preliminary c onsiderations and conclusions for alkali laser scaling are given.

Results obtained from a small discharge cross section (10×10 mm), high pressure (10 bar) TE CO₂ laser are presented demonstrating continuous wavelength tunability of the laser. Two arbitrary wavelength regions in the 9P and 10P branches are chosen to demonstrate the continuous tunability of the laser wavelength. Furthermore stability of the laser output is demonstrated over extended periods of operation. Other output parameters of the high pressure laser such as temporal pulse profile and peak pulse power were also measured. Preliminary results will be presented of a discharge system scaled to larger discharge cross sections intended for high pressure amplifiers in ultra short pulse terawatt laser systems. Electrode separations of up to 50 mm have been investigated with measured discharge widths of 80 mm. The system has been operated at gas pressures of up to 3.5 bar with various CO₂ laser gas mixtures. Discharge stability studies and gain measurements are reported.

The single-frequency two-level (SFTL) generation model was applied to predict the power extraction efficiency in electrically driven oxygen-iodine laser (EOIL). The analysis of the calculated and published experimental data showed that power extraction from the cw EOIL is limited by the rate of energy transfer from singlet oxygen molecules O₂(¹Δ) to iodine atoms I(²P_3/2) and about half of the produced singlet oxygen molecules were carried out from the resonator. To increase power extraction efficiency it will be necessary to substantially extend concentrations of singlet oxygen molecules and iodine atoms in the active medium of EOIL.

Application of two- and-three dimensional computational fluid dynamics (2D and 3D CFD) models to subsonic flowing-gas DPALs is reported. The 2D model is applied to a DPAL with optical resonator-flow field coaxial configuration and the 3D model is applied to an optical axis transverse to the flow configuration. The models take into account effects of temperature rise and losses of alkali atoms due to ionization. The 2D CFD model is applied to 1 kW flowing-gas Cs DPAL [A.V. Bogachev et al., Quantum Electron. 42, 95 (2012)] and the calculated results are in good agreement with the measurements. Comparison of the 2D CFD to semi-analytical model [B. D. Barmashenko and S. Rosenwaks, J. Opt. Soc. Am. B 30, 1118 (2013)] shows that for low pump power both models predict very close values of the laser power; however, at higher pump power, corresponding to saturation of the absorption of the pump transition, the laser power calculated using the 2D CFD model is much higher than that obtained using the semi-analytical model. At high pump power, the heat convection out of the laser resonator is more efficient for the transverse case than the coaxial case, the beam temperature is lower and consequently the calculated laser power is higher. Optimization of the Cs DPAL parameters, using 3D CFD modeling, shows that applying high flow velocity and narrowband pumping, maximum lasing power as high as 40 kW can be obtained at pump power of 80 kW for transverse flow configuration in a pumped volume of ~ 0.7 cm³.

Under cavity loss modulation, enormous dynamic behaviors will come up in B type cascade laser. In this paper, we built a two-wavelength cascade transition balanced equation model for CW HF chemical laser, 2P(5) and 1P(6) line were taken as cascade pair. We carried out cavity loss modulation experiment on a small scale supersonic discharge driven hydrogen fluoride chemical laser. From the view of phase space, we explained the characteristics by nonlinear time series analysis tools.

This paper describes systematically the properties of the surface discharge pumping source. The pre-ionization technology was investigated. The characteristics of the surface discharge and the photodissociation wave of exciting media have been studied. The temporal and Spatial Stability of discharge were measured and analyzed. The discharge spectral and ablation rate of three different materials were obtained.

Excimer laser has been shown to be efficient tools in plasma physics and material science. Recent progress on techniques of beam control in excimer laser system required for energy scaling are overviewed, Configuration and initial results of a 100J/10ns, 18 beam excimer laser system are given.

A theoretical procedure has been developed for evaluation of the diffraction efficiency of a Reflecting Volume-Bragg-Grating (RVBG) in accordance with Kogelnik’s theory. The diffraction features have been investigated for the different grating thicknesses, refractive index modulation, and grating spatial frequencies, respectively. The linewidths of a diffracted light and the effective diffraction efficiency have been studied while a certain linewidth in spectrum of an incident LD beam is taken into account in the calculation. The results are thought to be useful in the applications of single-longitudinal-mode (SLM) lasers and linewidth narrowing by means of RVBGs.

We report a quasi-CW linearly-polarized rubidium vapor laser. The pumping source consists of 5 laser diode bars and its linewidth is reduced from the raw 1.8 nm to 0.2 nm by a bulk Volume Bragg Grating (VBG). Instead of adopting the “quasi-waveguide structure” gain cell, the pumping light of the rubidium vapor laser propagates freely in the vapor cell. The pumping light with polarization perpendicular to one of the rubidium laser is coupled into the resonator cavity by the PBS. Output power of 10 W with good beam quality is realized. This laser configuration is suitable for a convection-cooling DPAL.

The supersonic nozzles lower temperature to 170-180 K better for the small signal gain coefficient. But at this temperature, the CO₂ buffer gas may become liquid state. A chemical oxygen-iodine laser (COIL) employing CO₂ as buffer gas and no-flake-nozzle was studied. Some mathematical simulation in three-dimensional computation fluid dynamics was adopted first to validate its usability. New nozzles gave the temperature higher than 400 K and considerable small signal gain coefficient. In the same conditions as simulation, experiments gave a 23% of chemical efficiency and 2.5 kW of output power. And it have got rid of “black area”, which was familiar in the supersonic COIL both in simulation and experimental results.

A traditional pressure recovery system is the major obstacle to mobile chemical oxygen-iodine laser (COIL) for its huge volume. A cryosorption vacuum pump was used as the pressure recovery system for different buffer gases. It made COIL become a flexible, quiet and pressure-tight. Experiments were carried out on a verti- COIL, which was designed for N₂ and energized by a square-pipe jet singlet oxygen generator (JSOG). The output power with CO₂ was 27.3% lower than that with N₂, but the zeolite bed showed an adsorption capacity threefold higher for CO₂ than for N₂ in the continuous operation. The great volume efficiency interested researchers.

Results of experimental measurements and numerical simulations of the N₂ and XeF₂ gas pressure effects on the gain characteristics are presented in the paper. It is experimentally and theoretically is shown that maximum total gain (5-6)×10⁴ achieved at a pump energy E = 240 J, 0.2 Torr XeF₂ and 0.5 atm N₂ pressure. Increasing and decreasing of N₂ pressure leads to decrease of the gain. The possibility of the XeF(C-A) amplifier operation in a generator mode is discussed and the theoretical study results of generation are presented. It is shown that an annular laser radiation with energy up to 8.5 J can be obtained. The study results of the influence on the laser energy of N₂ and XeF₂ pressure and reflectance coefficient of output mirror are presented.

Oxygen molecules existed in pairs under liquid condition, the radiation from vibrational ground state of ¹ Δ state to the first vibrational excited state of ³ ∑ state was electronic dipole moment transition allowed, and a photon with wavelength of 1580 nm was emitted. In our experiment, dye laser with wavelength of 581 nm, 634 nm, 764 nm was used to excite liquid oxygen to different excited states, while a tunable OPO was used as the seeder laser, and the small signal gain was measured to be 0.23 cm^-1, 0.3 cm^-1 and 0.076 cm^-1 respectively. The small signal gain (pump by photon of 634 nm) was significantly higher than that of common solid state lasers and chemical lasers. When the fundamental output of a Q-switched Nd:YAG laser was used as the pump source, the corresponding small signal gain was 0.12 cm^-1. The profiles of small signal gain form 1579.2 nm to 1580.8 nm were also presented. These results were consistent with theoretical calculation. The high positive gain indicated that the liquid oxygen was a potential medium for high energy laser. A comprehensive parameter optimization was still necessary in order to improve the mall signal gain.

An effective single line continuous wave HF chemical laser operation has been demonstrated using a Littrow-mounted diffractive grating cavity experimentally. Selection of spectral lines of the laser was investigated when the grating used as a reflector and an output mirror respectively. The feedback factor of the cavity is demonstrated important parameter of line selection. Output power of single line from grating cavity is obviously stronger than the same line within the full spectrum of the laser that operated without line selection.

A user-friendly data acquisition and control system (DACS) for a pulsed chemical oxygen -iodine laser (PCOIL) has been developed. It is implemented by an industrial control computer，a PLC, and a distributed input/output (I/O) module, as well as the valve and transmitter. The system is capable of handling 200 analogue/digital channels for performing various operations such as on-line acquisition, display, safety measures and control of various valves. These operations are controlled either by control switches configured on a PC while not running or by a pre-determined sequence or timings during the run. The system is capable of real-time acquisition and on-line estimation of important diagnostic parameters for optimization of a PCOIL. The DACS system has been programmed using software programmable logic controller (PLC). Using this DACS, more than 200 runs were given performed successfully.

An optical cavity temperature test method has been established for the HF chemical laser. This method assumes that in HF optical cavity the rotational distribution of vibrationally excited HF molecules meets the statistical thermodynamic distribution, the first overtones (v = 3-1 and 2-0) spontaneous emission spectral intensity distribution is obtained by using OMA V, the optical cavity temperature is calculated by linear fitting the rotational thermal equilibrium distribution formula for each HF vibrationally excited state. This method is simple, reliable, and repeatable. This method can be used to test the optical cavity temperature not only without lasing, but also with lasing.

Unstable resonator with nonuniform magnification for improving the beam uniformity of chemical oxygen iodine lasers is explored for the first time. The magnification of the resonator is a function of the radial coordinate of the polar coordinate system on the front mirror surface. A resonator was designed to have a lower magnification at the center of the resonator than at the edge. The resonator consists of two aspherical mirrors. Method for designing the resonator is given. The energy conservation law and the aplanatic condition were used to derive the designing principle of the two aspherical mirrors. The design result was fitted to polynomial form which is suitable for manufacturing. Numerical experiment was carried out to evaluate the performance of the resonator. The computation was based on coupled simulation of wave optics model and computational fluid mechanics model. Results proved the effectiveness of the design method. The design tends to enhance the intensity near the center of the output beam and cripple that near the edge. Further analysis revealed that this effect is induced because rays of light are reflected more densely at the center of the pupil than at the edge. Therefore, this design affords for a potential approach for improving the near field uniformity of chemical oxygen iodine lasers.

The visible and near infrared spectra of cavity chemiluminescence of a combustion driven HF laser fueled by NF₃ were collected and analyzed. The spectral line at 529 nm for the green chemiluminescence was attributed to electronic excited NF molecules in b¹∑ state, i.e. NF(b). The diffuse bands from 570 nm to 700 nm were attributed to the N₂(B-A) emission. The spectral lines from 850 nm to 1000 nm were attributed to the HF Δυ = 3 emission bands. At the end of every experiment, the spectral line at 874 nm would be observed, which was attributed to the electronic excited NF molecules in a¹ Δ state, i.e. NF(a). The NF(a-X) emission was found experimentally to be always avoiding the HFΔυ = 3 emission bands. It was also found experimentally that the NF(b-X) emission always accompanied the HF Δυ = 3 emission bands and their emission intensities had the same trends as a function of experimental time. Whereas the NF(a) molecules was produced in the optical cavity directly by the reaction of H atoms with NF₂ molecules in the incomplete combustion effluents, the NF(b) molecules were suggested to be produced mainly by the near resonant energy transfer from vibrational excited HF(v<=2) molecules to NF(a) molecules. In other words, the vibrational excited state HF(v<=2) molecules can be efficiently deactivated by the NF(a) molecules by near resonant V-E energy transfer process. Therefore we concluded that incomplete dissociation of NF₃ might be harmful to the HF(v<=2) population.

Results of experiments and modeling of CH₃I dissociation in a 40 MHz RF discharge in a discharge chamber of original design to produce iodine atoms for cw oxygen-iodine laser are presented. In experiments a substantial increase in CH₃I dissociation efficiency due to addition of oxygen into Ar:CH₃I mixture was observed. Complete CH₃I dissociation in Ar:CH3I:O2 mixture occurred at 200 W discharge power. Fraction of discharge power spent on iodine atoms production was equal to 16% at 0.17 mmol/s CH₃I flow rate. The rate of carbon atoms production as a function of molecular oxygen and water contents in CH₃I:Ar mixtures was studied with the help of numerical modeling. It was found that addition of water vapor resulted in increase while addition of molecular oxygen and HI in decrease of the rate of carbon atoms production. Due to diffusion most of carbon atoms had enough time to deposit on the walls of the discharge chamber. However, contrary to the situation in a DC discharge, in the RF discharge accumulation of carbon on the walls of the discharge chamber did not hamper discharge stability and iodine production, as it was observed in our experiments.

The experimental study of the amplification of stimulated Raman scattering (SRS) in high purity H₂ gas was demonstrated employing a Q-switched Nd:YAG laser at 1064 nm as the pump source. A part of the 1064 nm pump light (20% in energy) was focused into the first H₂ gas cell to generate the backward first Raman Stokes light (BS1), which is taken as the Raman seed light. The BS1 seed light combined to the residual pump light were focused into the second H₂ gas cell to get the amplification of the S1 1900 nm infrared Raman light. In this study, the maximum quantum conversion efficiency of the S1 light was estimated to be 76%. Under the condition of the same pump energy, especially for the low pump energy (lower than 40 mJ), the quantum conversion efficiency of the S1 light with the Raman seed light was significantly increased comparing to the single focus geometry (without the Raman seed light).

Sodium based excimer-pump alkali laser (Na-XPAL) is expected to be an efficient method to generate sodium beacon light, but the information about the spectroscopic characters of Na-XPAL remains sparse so far. In this work, we utilized the relative fluorescence intensity to study the absorption spectrum of blue satellites of complexes of sodium with different collision partners. The yellow fluorescence of Na D₁ and D₂ line was clearly visible. After processing the fluorescence intensity and the input pumping laser relative intensity, we obtained the Na-CH₄ system’s blue satellites was from 553nm to 556nm. Meanwhile, we experimentally demonstrated the Na-Ar and Na-Xe system’s wavelength range of blue satellites. Also, it was observed that the Na-Xe system’s absorption was stronger than the other two systems.

Stimulated Raman Scattering (SRS) is an effective means of laser wavelength conversion. Hydrogen is an excellent Raman medium for its high stimulated Raman gain coefficient and good flowability which can rapidly dissipate the heat generated by SRS process. In this paper we reported the H₂ SRS in multiple-pass cell pumped by the fundamental frequency output of a Q-switched Nd: YAG laser. Two concave reflection mirrors (with 1000 mm curvature radius and 50 mm diameter) were used in our experiment, both mirrors with a hole near the edge and were positioned to form co-center cavity, therefore the laser could repeatedly pass and refocus in the Raman cell to achieve a high SRS conversion efficiency and reduce SRS threshold for pump laser. By changing the pass number (1～17) of optical path in the Raman cell and the pump power(0～2.5MW), the Stokes conversion efficiency is optimized. Experimental results indicated that the Raman threshold was 0.178MW and the highest photon conversion efficiency was 50 %.

A dual-components absorption method based on absorption spectroscopy was described in the paper. It can easily eliminate the influence of the serious contamination and aerosol scattering on IFR measurement by utilizing the absorptions of iodine vapor and chlorine on two different wavelengths respectively. According to the character that there is no other gaseous product in the reaction besides iodine vapor, IFR in real time can be obtained by the connections of the pressure and the flow rate among chlorine remainder, iodine vapor, and the buffer gas. We used this method to measure IFR for the first time at the exit of a chemical iodine generator. The average of IFR is coincident with that calculated by chemical weighting mass.

Separation performance of a new spray-type singlet oxygen generator (SOG), named strongly swirling flow singlet oxygen generator (SSF-SOG), is studied by computational fluid dynamics (CFD) analysis and experiments. The flow field and the separation performance of the SSF-SOG are analyzed using Fluent® soft firstly, and the results show that the separation performance of SSF-SOG is effective for liquid droplets whose diameters are greater than 5μm. Then, using Phase Doppler Particle Analyzer (PDPA), the diameters of liquid droplets in reaction zone and gas outlet of SSF-SOG are measured. The results show that in the reaction zone the diameters of the liquid droplets mainly concentrated on 10μm, and only a little of droplets of which the diameter are under 5μm are detected in the gas outlet of SSF-SOG, which are well consistent with the results of the CFD analysis on SSF-SOG.

Two electrochemical methods for regeneration of Basic Hydrogen Peroxide (BHP) were investigated in this paper, which could be called one-step method and two-step method, respectively, distinguished by the number of steps during the regeneration process. The one-step method converts potassium chloride solution and oxygen directly to chlorine and BHP by a modified chlor-alkali cell with an oxygen cathode. For the one-step method, two reactors of different structure and corresponding regenerating process were designed. The experimental results showed that, for the continuous-type reactor, the highest peroxide concentration was 0.042 mol/L, while for batch-type reactor the highest peroxide concentration was 0.563 mol/L. The two-step method accomplishes the regeneration of BHP by a conventional chlor-alkali cell combined with a fuel cell reactor which could convert hydrogen and oxygen to peroxide in alkaline potassium hydroxide solution. A peroxide concentration of 2.450 mol/L was obtained for the two-step method.

High press, gravity-independent, singlet oxygen generator (HGSOG) ^[1] with small reaction zone and high chemical efficiency was designed and fabricated. The mixing, reaction and separation processes happened simultaneously in the reaction zone of HGSOG. The size and the configuration of reaction zone are very important for HGSOG. In this paper, p-τ value was calculated to determine the upper limit of the volume of reaction zone. The condition of gas-liquid separation was calculated to determine the lower limit of the volume of reaction zone. The utilization rate of Cl₂ achieved 90% and the yield of O₂(¹Δ) reached 70%.

Singlet oxygen generator (SOG) is the key part of chemical oxygen iodine laser (COIL) which supplies chemical energy for chemical oxygen iodine laser. A novel pre-swirling jet singlet oxygen generator (PJSOG) with rapid separation technology is put forward. In this paper, experimental performances of PJSOG have been studied by means of theoretical and experimental analysis. With excellent phase dispersion and rapid separation performances, PJSOG has several or several decade times specific area than traditional SOGs and high separation efficiency. It can reach more than 95% chlorine utilization and about 60% O₂ ( ¹Δ) yield. The operating stability has also been studied in this paper. The stable running time of PJSOG increased with liquid flow structure improvement. With high separation efficiency, high O₂ ( ¹Δ) output coefficient, high utilization coefficient of Cl₂ and excellent operating stability, the novel PJSOG must be a promising technology in further research.

Achieving population inversion through multi-photon cascade pumping is almost always difficult, and most laser medium work under 1-photon excitation mechanism. But for alkali atoms such as cesium, relatively large absorption cross sections of several low, cascading energy levels enable them properties such as up conversion. Here we carried out research on two-photon excitation alkali fluorescence. Two photons of near infrared region are used to excite alkali atoms to n ² D_5/2, n ² D_3/2 or higher energy levels, then the blue fluorescence of (n+1) ² P_3/2,(n+1) ² P_1/2→n ² S_1/2 are observed. Different pumping paths are tried and by the recorded spectra, transition routes of cesium are deducted and concluded. Finally the possibility of two-photon style DPALs (diode pumped alkali laser) are discussed, such alkali lasers can give output wavelengths in the shorter end of visual spectroscopy (400-460 nm) and are expected to get application in underwater communication and material laser processing.

A chemical oxygen-iodine laser (COIL) is an electronic transition, low pressure, high throughput system. The use of this laser demands a suitable pressure recovery system. This paper proposed a novel pressure recovery system based on chemical absorption and the feasibility for COIL with CO₂ as buffer gas (CO₂-COIL) was investigated. The novel pressure recovery system works by chemisorbing the CO₂-COIL effluents into two fixed-beds maintained at initial temperature of around 293-323K. Compared with the cryosorption system for N₂-COIL based on physical absorption, the novel chemisorptions based pressure recovery system has a simpler logistics and a shorter run-to-run preparation time. Two kinds of solid chemo-sorbents were designed and synthesized. One was used for chemisorbing the oxidizing gases such as O₂ ,Cl₂ and I₂, another was used for chemisorbing the acidic gas such as CO₂. The capacities of the two sorbents were measured to be 3.12 mmol（O₂）/g and 3.84 mmol (CO₂) /g, respectively. It indicated that the synthesized sorbents could effectively chemosorb the CO₂-COIL effluents. Secondly, analog test equipment was set up and used to study the feasibility of the novel pressure recovery system used for CO₂-COIL. The test results showed that the novel pressure recovery system could maintain the pressure under 6 Torr for tens seconds under the continuous gas flow. It showed that the novel pressure recovery system for CO₂-COIL based on chemical absorption is feasible.

We demonstrate the use of phase retrieval and Fraunhofer diffraction as a method for the measurement of laser beam quality. This technique involves using two CCD cameras to record a pair of conjugated light intensity images in defocus plane and one near field measurement instrument to record the light intensity image in near field. The wavefront is then retrieved using an optimization jointly constrained by them. Thereafter, combining with the known light intensity image in near field, light intensity image in focus plane can be figured out. After that, laser beam quality will be obtained by comparing with ideal light intensity distribution in focus plane. As light intensity images in defocus plane can be measured with higher resolution and lower CCD dynamic range than that in focus plane, this method is expected to give a precise laser beam quality.

Based on two-photon absorption, a 420nm blue laser of alkali Rb vapor was demonstrated, and a dye laser was used as the pumping laser. Utilizing the energy level structure of Rb atom, lasering mechanism and two-photon absorption process are analyzed. Absorbing two 778.1nm photons, Rb atoms were excited from 5² S_1/2 to 5² D_5/2, then relaxed to 6² P_3/2 with mid infrared photon radiation. 420nm blue laser was achieved by the transition 6² P_3/2→5² S_1/2. To improve efficiency of the blue laser, two-photon resonant excitation pumped alkali vapor blue lasers are proposed, which will be good beam quality, high efficiency and scalable blue lasers. The development of diode pumped alkali vapor blue laser is expected.

Using light radiation directly produced by combustion of some pyrotechnics as pumping sources of solid state lasers is a potentially effective way to obtain compact and high energy lasers. Kinetics of this kind of pumping is studied in terms of pulse energy and pulse time characteristics as well as laser output energy. Pumping kinetics is turned through changing fabrication methods of the pumping modules. It was found that the useful light energy and pulse time for the pyrotechnic pumping light showed opposite changing trend. Compressing pulse duration from 45 ms to about 10 ms would simultaneously cause 20%~ 50% decreases in useful light radiation energy. However, the laser output energy produced by these pumping sources only had a variation 9%, ranging from 427 mJ to 468 mJ. Reasons were related to the decrease in fluorescence loss in pumping energy below the threshold for the pyrotechnic modules having shorter pulse duration but higher radiation power.

Diode-pumped alkali vapor lasers are famous in the field of laser for their significant advantages such as very high quantum efficiency (Cs 99.5%, Rb 98.1%, K 95.2%), good thermal management performance and excellent beam output quality etc. A rate equation model fully considering the spatial distributions of pumping light and oscillating light is established under the hypothesis of quasi-two-level energy system of DPALs in this paper. Meanwhile, expressions of threshold pumping power, mode-matching efficiency and output power and slop efficiency in low pumping and strong pumping, respectively, are obtained. Then, the influences of mode-matching efficiency on working performance of DPALs are discussed and analyzed. Results show that mode-matching efficiency mainly impacts on threshold pumping power, output power and slop efficiency in low pumping but that nearly has no effects in strong pumping. Therefore, this model benefits the further research of DPALs.

Laser Ultrasonic Testing (UT) is an important technique for the non-destructive inspection of composite parts in the aerospace industry. In laser UT a high power, short pulse probe laser is scanned across the material surface, generating ultrasound waves which can be detected by a second low power laser system and are used to draw a defect map of the part. We report on the design and testing of a transversely excited atmospheric pressure (TEA) CO₂ laser system specifically optimised for laser UT. The laser is excited by a novel solid-state switched pulsing system and utilises either spark or corona preionisation. It provides short output pulses of less than 100 ns at repetition rates of up to 1 kHz, optimised for efficient ultrasonic wave generation. The system has been designed for highly reliable operation under industrial conditions and a long term test with total pulse counts in excess of 5 billion laser pulses is reported.

It was shown that run-away electron preionized volume (diffuse) discharge (REP DD) can be used as an excitation source of active gas mixtures at elevated pressures and can produce laser emission. We report experimental and calculated results of application of the REP DD for excitation of different active gas mixtures. It was shown that the REP DD allows to obtain efficient lasing stimulated radiation in the IR, visible and UV spectral ranges. Kinetic model of the REP DD in mixtures of nitrogen with SF₆ is developed allowing to predict the radiation parameters of nitrogen laser at 337.1 nm. Promising prospects of REP DD employment for exciting a series of gas lasers was demonstrated. Lasing was obtained on molecules N₂, HF, and DF with the efficiency close to the limiting value. It was established that the REP DD is most efficient for pumping lasers with the mixtures comprising electro-negative gases.

A hardware and a computative technique for tunable laser spectroscopy was developed for simultaneous measurement of Gaussian and Lorentian components of line broadening by fitting Voigt line profile. The technique was tested in measurements of pressure broadening coefficient for 811.5 nm Ar absorption line in a 40 MHz discharge in the pressure range 15-75 Torr with the help of tunable diode laser with a short external resonator. The obtained values for this coefficients reduced to 300 K are: ξ_Ar-Ar = (2.85±0.1)×10^-10 s^-1cm³ for broadening in the parent gas and ξ_Ar-He = (3.3±0.1)×10^-10 s^-1cm³ for broadening in helium. A good agreement with published results is observed. Measured Ar(1s₅) number density amounted to 10^-11cm^-3 for the discharge power density ~10 W cm^-3.

The design and performance of a closed cycle, repetitively pulsed HF/DF laser is described. For obtained higher stable laser pulse energy and running frequency, discharge stability with different electrode profile and different gas circulation structure are researched. The functional relations of laser pulse energy with electric field strength (E) and gas mixture pressure (P) for various gas flow velocity are studied. It is shown that with preliminary optimized of the gas injection segment structure before pump region and optimal E/P conditions, maximal running frequency of 100Hz is obtained and operating stability keeps well. Under these conditions, the laser average power is 40W and peak power is 4MW.