This PDF file contains the front matter associated with SPIE Proceedings Volume 7912, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We demonstrate a multi-channel architecture for nsec pulsed lidar transmitter, scalable to larger channel counts via wavelength- and time-multiplexing in a multi-stage Yb-fiber amplifier. This technology enables lidar systems for topographic mapping missions, requiring much greater spatial coverage and range resolution. We demonstrate prototype hardware, where wavelength channels at 1060nm, 1061nm and 1064nm are multiplexed, and precise 1.3nsec pulse using LiNbO₃ electro-optic(EO) modulators, at a combined repetition rate of 1MHz, with equal time interleaving between the wavelengths. The multiplexed pulses are amplified to >20W average power, in an optimized three-stage Yb-fiber amplifier system. We show simple de-multiplexing and frequency-doubling of one of the wavelengths (1064nm). Highspeed FPGA based control provides for independent and programmable control of the pulse rate, timing trigger, pulsewidth, and the intra-pulse-pattern for improved detection schemes.

Reliable, long term operation of high-power laser systems in the Earth orbit is not a straightforward task as the space environment entails various risks for optical surfaces and bulk materials. The increased operational risk is, among others, due to the presence of high energy radiation penetrating the metallic shielding of satellites and inducing absorption centers in the bulk of optical components, and vacuum exposure which can deteriorate coating performance. Comprehensive testing for analyzing high-energy radiation effects and mitigation procedures were performed on a set of frequency conversion crystals and are discussed in this paper. In addition to a general resistance to space environmental effects, the frequency conversion crystals were subjected to a comparative analysis on optimum third harmonic efficiency, starting from pulsed 1064 nm laser radiation, with the goal of exceeding a value of 30%. Concomitant modeling supported the selection of crystal parameters and the definition of crystal dimensions.

NASA Langley Research Center (LaRC) is working on a prototype laser system for simultaneous measurement of CO₂ and O₂ for planned Active Sensing of CO₂ Emissions over Nights, Days, and Seasons (ASCENDS) mission application. For this purpose, 1571 nm spectral band for CO₂ sensing and 1262 nm spectral band for oxygen sensing have been selected. In this paper, we discuss recent progress made in the development of single mode, compact and stable, seed laser technologies for CO₂ and O₂ transmitters. In particular, the development of an advanced distributed feedback laser (DFB) module master oscillator operating at 1571 nm, that is efficiently coupled to drive electronics and nano-cooling scheme in a single hermetically sealed package of volume less than 2" x 2" x 0.5", is presented.

Disk lasers combine high efficiency, excellent beam quality, high average and/or peak power with moderate cost and high reliability at multiple wavelengths, ranging from the infrared over the green to the ultraviolet. The demonstrated infrared average powers range from tens of kW in CW operation over >1 kW in ns pulses to >100 W in ps pulses and > 70 W in fs pulses. Wavelength conversion for nearly all modes of operation, e.g. 700 W@515nm in ns pulses, enlarges the fields of applications, making the disk technology today's most versatile laser platform.

The laser system is based on an Yb:YAG thin-disk regenerative amplifier, which is operated in different operation modes in order to address broad spectrum of pulse durations. It is especially interesting for application development tasks, when different pulse durations can be tested to find the application optimum. For sub-picosecond pulse duration the dispersion of the regenerative amplifier output is compensated with a pair of diffraction gratings. Pulses with a full width at half maximum of 334 fs at an output power level of 30 W can be produced using a nonlinear spectrum broadening during amplification. Tuning of the distance between gratings or abandoning of the compressor allows for output pulse durations of several picoseconds with an output power of 60 W. A second seed source allows for pulse durations up to several nanoseconds. Further, the amplifier was operated in cavity-dumped or in Q-switched mode just by changing of the electrical control of the Pockels cell in the amplifier. The pulse durations range is extended, correspondingly, to 100 ns and even to microseconds.

Operational performance of kilowatt-class thin-disk ceramic and single crystal Yb:Yag lasers is presented. High pump power is applied to various thin-disk assemblies on two different test beds. The assemblies are composed of ASE caps, 200μm gain media, and heat sinks made of SiC, sapphire, or diamond. A novel mounting and cooling process is described. FEA modeling of the assemblies is performed using COMSOL stress and thermal computations to understand and quantify thermal and stress effects on beam quality and laser output power. Under increased pump power, the thin-disk can deform 5-10 μm in the center, destroying cavity stability. This is observed experimentally. The results of this work indicate that a single thin-disk laser could simultaneously produce high beam quality and high power if novel thermal management techniques are employed.

The thin disk laser is a successful concept for high output power and/or high pulse energy, high efficiency and good beam quality in the 1 μm range. Holmium-doped materials are a promising approach to transform this success to the 2 μm range. Ho:YAG is especially interesting for high pulse energies due to the long fluorescence lifetime (~ 8 ms) which provides good energy storage capabilities. We have realized a Ho:YAG thin-disk laser with a cw output power of 15 W at 2.09 μm and a maximum optical-to-optical efficiency of 37%. The laser was pumped with a Tm-fiber laser. Numerical simulations are used for further characterization.

Using the well-known quasi-three level kinetics model of Beach^1,2 and Bourdet³ an exact analytical solution of the coupled medium and geometric, plane-wave optical propagation equations for a longitudinally or face-pumped CW laser is obtained. Although the quasi-three level kinetics model ignores all medium losses, e.g. amplified spontaneous emission, upconversion, and excited state absorption, it is applicable to Yb:YAG devices. The optical extraction model, which accounts for both laser wave amplification and pump wave absorption saturation coupling, treats both one- and two-face pumping as well as single-, double-, and multiple-reflections of the pump wave between the faces of the disk. Analytical expressions for the laser output power, the absorbed pump power, the threshold pump power, as well as the pump absorption, optical-to-optical, optical extraction, and slope efficiencies are obtained. With a suitable modification of the pump absorption efficiency, multiple-pass pumping via pump beam reinjection as achieved with a parabolic reflector by Stewen et al⁴ can also be treated. Explicit equations for determining the spatial distributions of the pump and laser intensities along the optic axis of the resonator are presented. Finally, explicit transcendental equations to determine the resonator outcoupling fraction which maximizes either the optical-to-optical or the optical extraction efficiency as a function of mirror loss, gain per pass, and pump power are derived. As an example the theory is applied to the Yb:YAG gain medium.

For special applications in spectroscopy, tunable single-frequency lasers are required to excite selectively relevant molecules. Amplified Yb:YAG disk lasers provide one opportunity for such lasers with a number of advantageous properties. Nevertheless, changing the wavelength from shot to shot at kHz repetition rates - desired e.g. for background subtraction or two-wavelength methods - remains challenging. We present results from two approaches, which in combination allow for fast wavelength switching of the oscillator and for extension of the tunability range of the laser system. For wavelength switching high voltage (some kV) is applied to a special birefringent filter (Lyot filter). Polarization rotation induced by the electric field yields losses at the wavelength emitted without voltage: the laser emits at a "new" wavelength with the highest gain. This new wavelength is determined by multiples of the free spectral range of the intra-cavity etalon used for single-frequency operation. The second stage of the laser system comprises an Yb:YAG regenerative amplifier. To ensure that parasitic lasing of this laser at the gain maximum is suppressed effectively, an additional birefringent filter is inserted into the amplifier. Adjusting this filter suppresses parasitic lasing and extends the tunability range of the system by a factor of more than 4.

Though the genesis of the disk laser concept dates to the early 90's, the disk laser continues to demonstrate the flexibility and the certain future of a breakthrough technology. On-going increases in power per disk, and improvements in beam quality and efficiency continue to validate the genius of the disk laser concept. As of today, the disk principle has not reached any fundamental limits regarding output power per disk or beam quality, and offers numerous advantages over other high power resonator concepts, especially over monolithic architectures. With well over 1000 high power disk lasers installations, the disk laser has proven to be a robust and reliable industrial tool. With advancements in running cost, investment cost and footprint, manufacturers continue to implement disk laser technology with more vigor than ever. This paper will explain important details of the TruDisk laser series and process relevant features of the system, like pump diode arrangement, resonator design and integrated beam guidance. In addition, advances in applications in the thick sheet area and very cost efficient high productivity applications like remote welding, remote cutting and cutting of thin sheets will be discussed.

We achieved 100mW cw of 593nm by intracavity sum frequency generation in a branched cavity, dual laser set up. Two gain media were used: Nd:YVO4 for generating 1342nm, diode-pumped by 3.7W at 808nm, and an optically pumped semiconductor chip (OPS), designed for 1064nm emission, diode-pumped by 1.7W at 808nm. Due to the short upperstate lifetime of the OPS, the generated 593nm output power was stable.A

Fiber MOPAs in the infrared wavelength region offer the advantage of high single mode output powers, independent selection of pulse repetition rates and pulse durations, and access to high repetition rates. Despite these performance advantages, most industrial and scientific applications in the visible and the ultraviolet spectral range are still dominated by solid state lasers. We will give an overview of the technical challenges of harmonic generation in fiber lasers and fiber amplifiers and discuss the state-of-the-art and future of Fiber MOPAs and bulk solid state lasers with harmonic generation.

Diode lasers have been demonstrated to operate over a great part of the visible spectrum: InGaN diodes cover the violet-blue- green part (<530 nm) and InGaAlP diodes cover the red part (>635 nm). Some fluorophorus in biotechnology applications are excited by intermediate wavelengths, from 540 to 630 nm. Optically pumped InGaAs lasers were demonstrated from 460 nm up to 580 nm. Standard frequency doubled diode pumped solid state (DPSS) lasers lack of suitable transition to cover the 565-650nm region. It is possible to modify the semiconductor composition to extend the frequency range or to frequency mix DPSS laser wavelengths, but it comes either with a significant R&D effort or with a complexity in the design. Raman scattering can red-shift the strong transitions of Nd or Yb lasers so that many wavelengths lying in the 1080-1300 nm range can be achieved. Recently several CW diode pumped Raman lasers were demonstrated, some of them including intra-cavity frequency doubling or mixing. The problems with these Raman lasers are the high pump threshold and the high noise. Based on monolithic cavities, we have built several visible Raman lasers with a reduced loss presenting a low pump threshold (<1W) and a high slope efficiency. Output powers in excess of 100 mW were achieved at 588 nm with a 2.5W 808 nm pump. Laser emissions from 556 nm up to more than 610 nm were demonstrated. Noise of these lasers was analyzed and means to reach low noise operation will be discussed at the conference.

We successfully drew a low-loss Dy-doped optical fiber (0.3dB/m at 532nm) of a waterproof fluoro-aluminate glass system and demonstrated yellow laser oscillation in the Dy³⁺-doped fluoride fiber pumped by a 398.8-nm GaN laser diode. The maximum output power was 10.3 mW and the slope efficiency was 17.1% at 575 nm. Since the fluoro-aluminate- glass system has a remarkable water resistance advantage compared to ZBLAN glass, Dy-doped fluoro-aluminate glass fiber is expected to contribute to making a solid-state yellow fiber laser with high chemical durability without a frequency doubling technique.

Extensive studies on frequency doubling with ppSLT crystals are presented. This includes a detailed discussion on design aspects and theoretical modeling predictions as well as experimental studies comparing the performance of ppSLT crystals from different providers with and without MgO doping. Experimental analyses of their acceptance parameters and crystal homogeneity are conducted with a pulsed microchip laser with low peak (6 kW) and low average power (50 mW) resulting in a maximum conversion efficiency of up to 80 % for high quality MgO doped crystals. Based on these results a compact converter module with fiber coupling is designed and tested with the radiation from the microchip laser and a fiber laser source in comparison. The fiber laser provides an average power of about 1 W. Even at this - still very moderate - power level a significant efficiency drop can be observed. Despite the advantage of higher pulse peak (25 kW) power from the fiber laser source, careful design adaptations of the converter are required even to preserve a conversion efficiency beyond 50%.

Ultrafast thin disk lasers achieve higher pulse energies and average power levels than any other modelocked oscillators. The key components of SESAM modelocked thin disk lasers are used in reflection, which is an advantage for the generation of ultrashort pulses with excellent temporal, spectral and spatial properties. We review the development and report latest results. We report on successful scaling of a Yb:Lu₂O₃ thin disk laser to 141 W average power, setting a new record for mode-locked laser oscillators. Such performance is important for a growing number of applications such as material processing or driving experiments in high field science.

A flexible ultrafast laser amplifier system based on Ytterbium Innoslab technology with an average power exceeding 200W is presented. The pulse duration of the system can be continuously tuned between 500fs and 6ps, limited only by the amplification bandwidth of Yb:YAG and the stretcher of the seed source. The repetition rate can be varied from 26.6MHz down to 1MHz. For the ps-regime more than 200μJ and for the fs-regime more than 50μJ are demonstrated without the need of temporal compression of the high power beam after the amplifier. Spectral bandwidth is close to the transform limit of the shortest measured pulses. Beam quality is measured to be near the diffraction limit (M²<1.3).

To scale the power of picosecond laser an oscillator and amplifier system has been developed. The amplifier consists of preamplifier and end amplifier. Both amplifiers are based on INNOSLAB amplifier. With the oscillator/amplifier system higher than 400W average power and max pulse energy of 1mJ was obtained. In this paper the design and the results will be presented and discussed.

Many industrial and scientific applications need ultra-short pulses with high average power. Diode-pumped systems based on ytterbium-doped crystals have a huge interest thanks to their good thermal and spectroscopic properties. Among them, Yb:CALGO and Yb:CaF₂, hold exceptional positions exhibiting a very atypical combination of ultrabroad bandwidth and high thermal conductivity, therefore very promising for short pulse and high power applications. In this paper we present an overview of the results obtained with these two crystals. First, we detail the origin of this exceptional gathering of their broad emission bands and good thermal properties. Second, we present the results obtained in femtosecond regime with these two crystals including a discussion on the actual limitations of Yb-doped ultrafast solid-state lasers.

Laser sources of high average power are essential to transfer femtosecond technology to industrial applications. We demonstrate a compact diode-pumped Yb:KGW femtosecond oscillator-Yb:YAG Innoslab amplifier MOPA with nearly transform and diffraction limited 636 fs pulses at 620 W average output power and 20 MHz repetition rate. By cascading two amplifiers an average output power of 1.1 kW and peak power of 80 MW is achieved in a single, linearly polarized beam. The MOPA is operated at room temperature and no CPA technique is used. The specific properties of Innoslab MOPAs are compared with fibers and thin-disks.

Many industrial and scientific applications need ultra-short and energetic pulses. Diode-pumped systems based on ytterbium-doped crystals have a huge interest thanks to their good thermal and spectroscopic properties. Among them, Yb:CaF₂, shows very promising results for short pulse generation, and its long fluorescence lifetime, 2.4 ms, indicates a high energy storage capacity. We present a diode-pumped regenerative amplifier based on an Yb:CaF₂ crystal optimized to produce short pulses for various repetition rates ranging from 100 Hz to 10 kHz. The experiment is performed with a 2.6-% Yb doped 5-mm-long CaF₂ crystal grown by using the Bridgman technique and used at Brewster angle. To optimize the injection pulse spectrum in terms of bandwidth and maximum gain, the seed pulses are generated by a broadband Yb:CALGO oscillator centered at 1043 nm with a FWHM bandwidth of 15 nm at a repetition rate of 27 MHz. The pulses are then stretched to 260 ps with a transmission grating. The shortest pulse duration generated is 178-fs, and the corresponding energy is 1.4 mJ before compression (620 μJ after), at a repetition rate of 500 Hz for 16 W of pump power. The bandwidth is 10 nm centered at 1040 nm. At 10 kHz repetition rate, 1.4 W of average power before compression is obtained, corresponding to an optical-optical efficiency of 10%. We also noticed that the pulse duration tends to increase above 1 kHz, reaching 400 fs at 10 kHz.

Passive mode-locking of Nd-lasers operating on the ⁴F_3/2 → ₄I_13/2 transition is problematic for semiconductor saturable absorber mirrors (SESAMs) not only because of difficulties in their fabrication process but also in relation to the achievable parameters and damage resistivity. We investigate an alternative approach based on second-order nonlinearity inside the laser cavity which utilizes negative χ⁽²⁾-lens formation in a SHG crystal assisted by nonlinear reflection of the so-called "frequency-doubling nonlinear-mirror" (FDNLM). This approach has been previously employed only for mode-locking of Nd-lasers emitting at 1.06 μm. Here we demonstrate passive mode-locking of a diode-pumped Nd:YVO₄ laser operating at 1342 nm based on negative &chi^;(2)-lensing assisted by the FDNLM effect. Using a 7-mm-long BiB₃O₆ (BIBO) nonlinear crystal or 10-mm-long and 1-mm-thick periodically-poled Mg-doped stoichiometric lithium tantalate (PPMgSLT) crystal and output couplers highly-reflecting at the second-harmonic with optimized transmission at the fundamental, we achieve average output powers in the steady-state mode-locked regime of the order of 1 W at pulse durations in the 4-7 ps range. Such a combination of high output power and short pulse duration is superior with respect to the results previously reported with SESAM mode-locked Nd-lasers operating on this transition. Higher average powers have been obtained for this laser transition only by the complex additive mode-locking technique. In our case the average power limit is set by the maximum power achievable in the fundamental transversal mode in the continuous-wave (CW) regime. The shortest pulses (FWHM of 3.7 ps) can be very well fitted by sech² temporal shape assumption.

A Joule-class, narrow-linewidth amplifier line delivering 20 ns pulses with a TEM00 spatial profile is presented. A Q-switched Nd:YAG oscillator with an intra-cavity volume Bragg grating (VBG) is used to seed the amplifier line. A series of flashlamp-pumped Nd:YAG amplifiers consisting of a double-pass and two single-pass amplifiers boost the energy of the 21 ns pulses to 480 mJ. The presented amplifier line will be used for fundamental studies including remote Raman spectroscopy and ns filamentation.

Because of their high absorptions UV lasers are widely used for precision machining in LED, and micro electronic production. To increase productivity high average power of UV lasers are required. Lasers with pulse energy and short pulse are favourable for UV sources through third and forth harmonic generation. Using an INNOSLAB laser more than 50W at 355nm and more than 30W at 266nm have been obtained. In this paper the experimental results will be presented and discussed.

Synchronized Q-switching between quasi-three-level and four-level lasers is interesting for sum-frequency generation into the blue and ultraviolet. We report, for the first time, stable synchronized Q-switching between a quasi-three-level laser at 946 nm and a four-level laser at 1064 nm in an all passive approach. While timing jitter of the individual freerunning lasers were on the order of 10 μs, the relative timing jitter, defined as one standard-deviation of the experimental data, was only 9 ns between the two synchronized pulses. The minimum delay between the two pulses was 64 ns during stable operation, which gave a 79% temporal overlap when normalized against the zero-delay scenario. Preliminary results show promise for non-linear frequency conversion, which could lead to high power pulsed blue and ultraviolet lasers.

The method of optical triggering using a brass board architecture for a Q-switched Nd:YAG laser by direct bleaching of a Cr:YAG saturable absorber was determined to be effective in reducing the pulse-to-pulse timing jitter. A miniaturized triggering setup was employed to enable the brass board operation of the optically triggered laser. A 3mm wide minilaser diode bar (1024nm) with collimated emission was mounted on a compact heat sink and used to bleach the Cr:YAG saturable absorber from a direction orthogonal to the lasing axis. A compact 300A pulse driver, with <0.5 μs rise time and 3-5 μs duration, was developed for pulsing the 3mm diode bar. These components were combined to demonstrate a compact brassboard implementation of the optically triggered passively Q-switched laser.

High power 808 nm VCSEL arrays were developed to pump compact pulsed Nd:YAG lasers. A QCW side-pumped passively Q-switched Nd:YAG laser operating at 1064 nm produced linearly polarized 4 ns IR pulses with 4.7 mJ pulse energy. These pulses were externally frequency doubled and quadrupled resulting in 2.5 mJ pulse energy at 532 nm and 0.8 mJ at 266 nm respectively. A similar but actively Q-switched dual side-pumped Nd:YAG laser operating at the weaker quasi three-level 946 nm transition produced 12 mJ pulses that were efficiently frequency doubled resulting in 5.6 mJ blue pulses of 17 ns duration.

We report on a Nd:YVO₄ regenerative amplifier (RA), end pumped by 888 nm-diode lasers. The output power was about 46W at repetition rates from 150 to 833kHz with an M²-factor of 1.2. The amplifier was seeded by a gain switched diode laser, generating pulses with a duration of 65 ps and a pulse energy of ≈ 5 pJ. The high gain of the RA of more than 70 dB provides amplified pulse energies as high as 180μJ. Bifurcations of the pulse energy could be avoided. Pulse amplitude fluctuations of only 1.2% for 10,000 consecutive pulses were measured. The long term output power stability of the laboratory setup was 0.3%.

Light scatter due to surface defects on laser resonator optics produces losses which lower system efficiency and output power. The traditional methodology for surface quality inspection involves visual comparison of a component to scratch and dig (SAD) standards under controlled lighting and viewing conditions. Unfortunately, this process is subjective and operator dependent. Also, there is no clear correlation between inspection results and the actual performance impact of the optic in a laser resonator. As a result, laser manufacturers often overspecify surface quality in order to ensure that optics will not degrade laser performance due to scatter. This can drive up component costs and lengthen lead times. Alternatively, an objective test system for measuring optical scatter from defects can be constructed with a microscope, calibrated lighting, a CCD detector and image processing software. This approach is quantitative, highly repeatable and totally operator independent. Furthermore, it is flexible, allowing the user to set threshold levels as to what will or will not constitute a defect. This paper details how this automated, quantitative type of surface quality measurement can be constructed, and shows how its results correlate against conventional loss measurement techniques such as cavity ringdown times.

Ultrashort pulse fiber delivery for Ti:Sapphire lasers is basically restricted to distances below a few meters which is due to the application of dispersion compensating devices that are not capable of managing third and higher order material dispersion. By the use of a fiber delivery concept based on higher order mode fibers ultrashort laser pulses in the 800 nm wavelength range are transmitted over 20 meters without the need for pulse pre-chirping. For the first time a large distance fiber delivery module is demonstrated, revealing its potential for remote THz imaging or spectroscopy using ultrashort laser pulses. Application of the fiber delivery is demonstrated by generating and detecting broadband THz radiation at the fiber output.

For high precision beam steering usually complex and sophisticated mechanics are necessary to keep the alignment long term stable. Here we present a simple temperature controlled steering device based on a crystal with different temperature expansion coefficients in its axes. Results for single mode fiber coupling of visible lasers will be presented.

High laser power levels in combination with increasing beam quality bring optics performance into focus, particularly with regard to systems with low focal shifts along the optical axis. In industrial applications, this often influences the overall performance of the process, especially if the focal shift is comparable to or in excess of the Rayleigh length. It is commonly accepted that the focal shifts are of thermal nature where lens material, lens coating, geometry and surface contamination all contribute to the direction and extent of the focal shifts. In this paper we will present a novel design of lens packages where a patented all-in-quartz concept is explored. By mounting quartz lenses in hermetically sealed quartz tubes and applying water cooling on the perimeter of the quartz tubes we will reduce or eliminate a number of contributing factors to focal shift problems. The hermetic sealing, carried out in a clean-room environment, will minimize lens surface contamination. Differences in thermal expansion between lens and housing are eliminated as the lens and housing will be of the same material. Absorption of scattered laser light will be efficient as the energy is removed quickly by cooling water and not absorbed by fixed surroundings. Finally, indirect heating from the housing transmitted by radiation and convection to the lenses is avoided. Values of the normalized System Focal Shift Factors (SFSF) for the all-in-quartz optics will be compared to standard lens assemblies at multi-kW laser power levels.

In most applications of laser technology and optics the beam quality, the ability to focus a laser beam and the achievement of a good optical resolution play an important role. For the compensation of distortions adaptive optics is used. Classical adaptive-optics control schemes use matrix operations, which show a non-linear computation time dependence with matrix size, making it difficult to achieve high control loop frequencies at high resolution. A novel closed-loop adaptive optics is presented using a massively-parallel neural network in an all-hardware setup. It can be used for a fast real-time wave front sensor and for closed-loop operation.

Adhesive-free bonded (AFB®) un-doped end-capped and segmentally bonded Tm:YLF laser composites have been investigated for high efficiency LD-pumped laser operations. With a fiber coupled 792-nm diode laser as pump source and a single-end pump arrangement, an optical-to-optical laser efficiency of 48.3% (quantum efficiency of 116%) and a slope efficiency of 55% (quantum efficiency of 132%) have been measured at the laser output wavelength of 1.908 μm. A maximum laser output power up to 29 W has been also achieved before the thermal stress fracture limit. The high laser efficiencies and output power can be attributed to the two-for-one cross-relaxation process and the efficient thermal management of the AFB laser composites.

We report an optimization of Fe:ZnSe crystals fabrication, as well as a fourfold increase of the output energy of the gain-switched middle-infrared Fe:ZnSe laser pumped by the radiation of Q-switched Cr:Er:YSGG (2.8μm) laser. Lasing was studied over 236-300K temperature range. In Fabry-Perot cavity with 18% OC reflectivity the maximum output energy reached 4.7 mJ @ 4.3μm and 3.6 mJ @ 4.37μm at 236K and 300K, respectively and was limited only by available pump energy. Threshold was about 8 mJ and was practically unchanged over studied temperature range. The laser slope efficiencies decreased from 19% to 16 % with an increase of temperature from 236 to 300K.

A conductively cooled 970nm laser diode bar primarily designed for quasi continuous wave (qcw) pumping of miniaturized solid state lasers is presented. The robust chip design and the highly efficient two side cooling setup of the 10x12x5mm³ diode assembly allows output peak power levels as high as 600W at 500A drive current and 1% duty cycle. The high performance laser diode was employed as pump for a miniaturized, conductively cooled, side pumped Er:YAG laser system. The laser system, with an overall dimensions of 30x25x17mm3, generates 2.8W average power with M²<5.

In this paper, we report record nanosecond output energies of gain-switched Cr:ZnSe lasers pumped by Q-switched Cr:Tm:Ho:YAG (100 ns @ 2.096 μm) and Raman shifted Nd:YAG lasers (7 ns @ 1.906 μm). In these experiments we used Brewster cut Cr:ZnSe gain elements with a chromium concentration of 8x10¹⁸ cm^-3. Under Cr:Tm:Ho:YAG pumping, the first Cr:ZnSe laser demonstrated 3.1 mJ of output energy, 52% slope efficiency and 110 nm linewidth centered at a wavelength of 2.47 μm. Maximum output energy of the second Cr:ZnSe laser reached 10.1 mJ under H₂ Raman shifted Nd:YAG laser pumping. The slope efficiency estimated from the input-output data was 47%.

To realize the goal of mid-infrared lasing in rare-earth-ion-doped chalcogenide glass fibers, it is important to achieve as large a concentration as possible of the rare earth ion dopants in the host chalcogenide glass matrix, while minimizing optical loss. However, when a large amount of rare earth dopant is added to the chalcogenide glass, solubility problems can emerge which decrease glass stability and also impair optical properties. In this paper, the nature of the rare earth additive is demonstrated to be pivotal, affecting both the chalcogenide glass stability and the optical scattering loss. Dysprosium in the form of dysprosium metal foil, or as the salt dysprosium trichloride, is added to the Ge_16.5As₉Ga₁₀Se_64.5 batch and glasses are obtained using the melt-cool method. The nominal Dy³⁺ concentration is 2000 ppm. The glass melting results, and powder X-ray diffraction and Fourier transform infrared spectrometry characterization of the products, indicate major improvement in bulk glass stability, glass surface quality and optical loss when the dysprosium additive to the glass batch is in the form of Dy⁰ (metal foil) rather than Dy^IIICl₃. Reasons for this improvement are suggested.

We describe an efficient laser emission from a directly grown Er³⁺:YAG single-crystal fiber that is resonantly pumped using a continuous-wave (CW) laser diode at 1532 nm. In a longitudinal pumping, it emits 12.5 W at 1645 nm with a slope efficiency of 32%, which is the highest ever reported for a directly grown Er:YAG single-crystal fiber laser. Using an off-axis pumping scheme, CW output powers up to 7.3 W can be reached and in Q-switched operation, the laser produces 2 mJ pulses with a duration of 38 ns at the repetition rate of 1 kHz with an M² factor below 1.8. To our knowledge this is the first directly grown Er³⁺:YAG single-crystal fiber Q-switched laser.

Middle infrared (mid-IR) chromium-doped zinc selenide (Cr:ZnSe) bulk lasers have attracted a lot of attention due to their unique combination of optical and laser properties facilitating a wide range of potential scientific, industrial, and medical applications. Utilization of thin film waveguide geometry enabling good thermal management and control of beam quality is a viable pathway for compact chip-integrated optical laser design. Cr:ZnSe thin films are also promising as saturable absorbers and mode-lockers of the cavities of solid state lasers operating over 1.3-2.1 μm. We recently reported the first successful demonstration of mid-IR Cr:ZnSe planar waveguide lasing at 2.6 μm under gain-switched short-pulse (5 ns) 1.56 μm excitation as well as the passive Q-switching of the cavity of a fiber-pumped Er:YAG laser operating at 1645 nm using a highly doped Cr:ZnSe thin film. PLD grown Cr:ZnSe waveguide were fabricated on sapphire substrates (Cr:ZnSe/sapphire) with chromium concentration of 10¹⁸-10¹⁹ cm^-3. Further development of mid-IR lasing in the Cr:ZnSe planar waveguide under continuous wave excitation were investigated. In addition, deposition of Cr:ZnSe-based thin film structures on n-type GaAs substrates were also investigated for possible mid-IR electroluminescence.

Compact solid-state laser systems based on chromium doped II-VI semiconductor materials (ZnS, ZnSe, CdSe) with tunability over 2-3.6 μm, output power exceeding 10W, and efficiency up to 70% were demonstrated recently. A further increase of the output power requires a thorough thermal management of the active element. Fiber geometry of gain element is very promising among other different approaches to control beam quality and thermal lensing. The proposed transition metal doped ZnS:ZnSe/As2S3:As2Se3 composite materials with index matching of II-VI and V-VI components represent a new way for design of mid-infrared laser active fibers. Chalcogenide glasses have wide transparency range in mid-IR, enable fiber geometry, and their refractive index can be varied from n=2.1 to n=2.5 matching refractive index of ZnS (n=2.26) and ZnSe (n=2.44) crystals and eliminating scattering losses. The II-VI compounds provide a tetrahedral coordination of the chromium ions required for mid-IR lasing. We report the first mid-IR laser active Cr:ZnSe/As₂S₃:As₂Se₃ composites fabrication and room-temperature lasing at 2.4 μm. The Cr:ZnSe/As₂S₃:As₂Se₃ composites were prepared by annealing of the appropriate compounds under vacuum and by casting and drying of Cr:ZnSe microparticles suspension in As₂S₃:As₂Se₃ propylamine solution. All samples demonstrated mid-IR photoluminescence typical for Cr²⁺ ions in ZnSe host. High optical gain and low passive losses in Cr:ZnSe/As₂S₃:As₂Se₃ composite material were demonstrated in random lasing experiments.

Current state-of-the-art and next generation laser systems-such as those used in the NIF and LIFE experiments at LLNL-depend on ever larger optical elements. The need for wide aperture optics that are tolerant of high power has placed many demands on material growers for such diverse materials as crystalline sapphire, quartz, and laser host materials. For such materials, it is either prohibitively expensive or even physically impossible to fabricate monolithic pieces with the required size. In these cases, it is preferable to optically bond two or more elements together with a technique such as Chemically Activated Direct Bonding (CADB©). CADB is an epoxy-free bonding method that produces bulk-strength bonded samples with negligible optical loss and excellent environmental robustness. The authors have demonstrated CADB for a variety of different laser glasses and crystals. For this project, we will bond quartz samples together to determine the suitability of the resulting assemblies for large aperture high power laser optics. The assemblies will be evaluated in terms of their transmitted wavefront error, and other optical properties.

We show spectroscopic and lasing properties of new ytterbium-doped borate compounds with the structure Li₆(Gd_{(1- x)}Y_x)_0.75Yb_0.25(BO₃)₃ with x = 0, 0.25, 0.5, 0.75 and 1, respectively. All compounds show large emission spectra suitable for femtosecond pulse generation. We studied the laser performances in a diode-pumped linear laser cavity on about 1- mm-thick crystal samples having an ytterbium doping concentration of 22 %. The compounds show all cw lasing at wavelengths around 1040 to 1060 nm with a slope efficiency of 32 %. The maximum observed output power was 460 mW at an incident pump power of 1.6 W at 972 nm.

For future satellite based water vapor DIAL systems efficient and rugged sources preferably around 935 nm are required. Especially for the WALES system (Water Vapour Lidar Experiment in Space) four wavelengths between 935.561 nm and 935.906 nm (vac.) have to be addressed. A promising candidate for the direct generation within this spectral range is a simple diode pumped setup based on compositionally tuned neodymium-doped mixed garnet crystals. Within the scope of this work, novel Nd:(Y_xLu_1-x)₃Ga₅O₁₂-crystals (Nd:YLuGG) with different compositions (0≤x≤1) were investigated. Beside the characterization of some relevant crystal properties laser experiments in quasi-continuous operation, Qswitched operation and in single-longitudinal-mode operation were performed. By the R2-Z5-transition wavelengths between 935.3 nm and 936.6 nm (vac.) can be addressed with different compositions x. At a repetition rate of 100 Hz nearly 6 mJ were extracted in longitudinal multimode around 935.7 nm (vac.) from a Nd:(Y_0.58Lu_0.42)₃Ga₅O₁₂-crystal. The cavity was injection seeded and stabilized with the ramp-and-fire-method to obtain single frequency radiation. At 935.7 nm more than 4.7 mJ were generated. The laser could be tuned over a range of about ± 0.22 nm in single-longitudinal- mode operation.

Cryogenic cooling is a very interesting and promising apparatus for high power lasers, especially with Yb-doped materials. In fact, it is now well known that operating this type of laser materials at cryogenic temperatures such as 77K (liquid nitrogen temperature) positively affects their performance, especially at high power levels, because of increased thermal conductivities and absorption and emission cross sections. We present a high-power diode-pumped Yb:CaF₂ laser operating at cryogenic temperature (77 K). A laser output power of 97 W at 1034 nm was extracted for a pump power of 245 W. The corresponding global extraction efficiency (versus absorbed pump power) is 65%. The laser small signal gain was found equal to 3.1. The laser wavelength could be tuned between 990 and 1052 nm with peaks which well correspond to the structure of the gain cross section spectra registered at low temperature.

We developed a cryogenically cooled Yb:YAG laser as the pump beam for a pulsed Raman laser based on CVD grown diamond crystals. The Q-switched cryogenic Yb-doped YAG 1030 nm pump laser delivered 340 W at 40 kHz with diffraction-limited beam quality, with an optical efficiency of 80%. The record average power of 24.5 W was generated from the Raman laser at 1193 nm. Modeling of the performance confirmed the corresponding Raman gain coefficient, 13.5 cm/GW. The laser was operated at room temperature and under cryogenic cooling at 77 K, with equal performance.

Ceramic laser materials have come a long way since the first demonstration of lasing in 1964. Improvements in powder synthesis and ceramic sintering as well as novel ideas have led to notable achievements. These include the first Nd:YAG ceramic laser in 1995, breaking the 1 KW mark in 2002 and then the remarkable demonstration of more than 100 KW output power from a YAG ceramic laser system in 2009. Additional developments have included highly doped microchip lasers, ultrashort pulse lasers, novel materials such as sesquioxides, fluoride ceramic lasers, selenide ceramic lasers in the 2 to 3 μm region, composite ceramic lasers for better thermal management, and single crystal lasers derived from polycrystalline ceramics. This paper highlights some of these notable achievements.

One at% Yb:CaF₂ transparent ceramics for high power lasers are obtained by vacuum sintering and hot pressing nanoparticles synthesized through a soft chemistry route. The residual optical losses of these ceramics are as low as 0.09 cm^-1 (corresponding to an in-line transmittance of 96.7%) at 1200 nm. Densification during sintering is limited by large voids, but pressure assisted densification after sintering results in high optical quality transparent ceramics. Absorption spectra are similar to Yb:CaF₂ single crystal, and the fluorescence lifetime was measured to be 2 ms in the wavelength 1010 to 1050 nm range. The 1 at% Yb:CaF2 transparent ceramics successfully produced laser oscillation at 1031 nm when placed in an Omega-type laser cavity under 970 nm diode laser pumping.

Polycrystalline YAG fibers are of interest for both optical and structural applications. Various processing routes of YAG fibers for structural applications have been explored; however, processing routes for optical quality polycrystalline YAG fiber have not been investigated intensively despite the potential of the material to enable high power lasers. Recent results in the processing of YAG fiber for laser applications are presented and detailed relationship between processes, microstructures, and optical properties of YAG fibers are discussed. Specifically, details of the processes for green fiber preparation, sintering methods, and transparencies depending on the process variables are shown. Our recent advancement in fiber processing prior to sintering has improved the transparency of YAG fiber significantly. Vacuum or air sintering followed by Hot Isostatic Press (HIP) produced fibers with transparency comparable to that of single crystal YAG fiber.

A theoretical investigation of the metrological characteristics of a precision Fresnel attenuator is performed for the purpose of determining whether it can be employed as a comparison standard intended for comparing the domestic primary standard of the unit of mean power of continuous laser radiation with an absolute cryogenic radiometer.

Laser characteristics of Pr:YAlO3 microchip laser operating in the near-infrared spectral region are reported. For active medium pumping, GaN laser diode providing up to 1 W of output power at ~448 nm was employed. Microchip resonator was formed by dielectric mirrors directly deposited on the Pr:YAlO3 crystal surfaces. The continuous-wave output radiation at 747 nm with maximum power of 139 mW has been extracted from the microchip laser system. Slope efficiency related to the incident pumping power was 25%.

This work presents the mechanisms adopted for the design of micro-second pulsed laser mode for a CW Self-Raman laser cavity in 586nm and 4W output power. The new technique for retina disease treatment discharges laser pulses on the retina tissue, in laser sequences of 200 μs pulse duration at each 2ms. This operation mode requires the laser to discharge fast electric pulses, making the system control velocity of the electronic system cavity vital. The control procedures to keep the laser output power stable and the laser head behavior in micro-second pulse mode are presented.

This article describes the generation of the laser facula, and analyzes the energy characteristics of the facula. A testing device is designed to measure the facula of the laser light in the far distance, and the system can collect and analyze the laser facula. The testing system sets by the laser ranger finder, thousands of meters away from the target. A near infrared CCD (Charge Coupled Device) camera of high sensitivity is used to collect the facula of 1.06μm laser. Add a filter of 1.06μm before the CCD camera to get more accurate infrared information. A beam of the laser ranger finder shoots to the target. A infrared CCD and the laser ranger finder is synchronizing triggered. For real-time observation of the background, the system use another ordinary CCD and telephoto lenses. A series of laser facula which is collected by the infrared CCD is stored into computer as the form of bitmaps. The testing device uses median filter to denoise the facula pictures and use image processing to analyze the gray-scale of facula, thus the device can get the intensity distribution, the centroid position and its variation with the spot. The device uses image fusion to realize the background integration of white-light CCD and infrared CCD images.