A QCW 100 W LD array side pumped high power laser has been developed. The 1.06 micrometer laser pulse energy of 2 mJ, with the pulse width 20 ns and repetition frequency 70 Hz to approximately 5 KHz is obtained. Using the non-cylinder lens focus system developed by our group, the efficient conversion of pump energy into 1.06 micrometer TEM00 mode is achieved with 17% optical-optical efficiency. The effect of vibrating output coupler in the laser resonator strengths the output power has been found for the first time.
The spectroscopic properties and 3-micrometer lasing of Er3+ doped in yttrium vanadate (YVO4) were investigated in this paper. It is found that the Er3+ concentration has a negative effect on the emission of the transition 4I13/2 yields 4I15/2 (1.55 micrometer), and a positive effect on that of the 4I11/2 yields 4I13/2 transition (2.68 micrometer). With direct upper-state pumping and a plane-concave cavity a self terminating laser was achieved at the wavelength of 2.724 micrometer in the 30 at.% Er3+ doped sample. No laser activities were realized in the crystals with lower Er3+ concentrations. The laser activities of Er3+:YVO4 and Er:YAG were compared and the differences between both were discussed on the basis of the features of the upper and lower state and the population dynamics of the two levels. It is proposed that the lack of effective cross relaxations between ions in the 4I13/2 state in the Er3+:YVO4 are responsible for the termination of its 3 micrometer laser. The possible ways to improve the laser behavior were also suggested based on the discussions.
A diode-laser side-pumped E-O Q-switched TEM00 Nd:YAG slab laser that uses a large N.A. cylindrical lens and a thin slab pumping geometry has been investigated. The pumping scheme has the ability to match well the pump beam to the laser's fundamental transverse mode in two axes. Approximately 1.1 times diffraction limited laser beam is obtained. The slope efficiency is 31% and 18.9% at long-pump and Q-switched operation, respectively.
A novel structure for multiple wavelength operation and narrow line-width ring Er-doped fiber laser, in which the multiple fiber gratings are in series connection, is proposed. The feasibility of this new structure is confirmed in experiment and the stable operation of dual wavelength is obtained.
The properties of laser using Er:YLiF4 and Er:YVO4 crystals at approximately 1.6 micrometer wavelength are studied by equations deduced from speed equations. The results indicate that the laser threshold energies of Er:YLiF4 and Er:YVO4 are 4.4 and 2.0 times respectively lower than that of Er:YAG. The slope efficiencies of Er:YLiF4 and Er:YVO4 crystals are 3.7 and 1.5 times higher respectively than that of Er:YAG crystal. Therefore the YVO4, especially the YLiF4 crystal is a fine host crystal doped Er3+ ions, whose threshold is low and slope efficiency is high.
A self-made diode-pumped Nd:YAG-KTP laser is frequency stabilized by locking its intracavity-doubled output to the center of Doppler-broadened transitions of molecular iodine near 532 nm. The first harmonic locking induces dither of the laser frequency and the external FM spectroscopy locking is in progress. The laser system and locking technique are simple and can be attractive for certain applications.
A diode-pumped monolithic quasi-planar ring laser is being developed using Nd:YAG crystal. Theoretical analysis was carried out based on the calculation of eigenvectors and eigenvalues of Jones matrix. To maximize the differential loss, the optimization for the crystal dimensions and the out- of-plane angle is taken. Unidirectional oscillation and single mode operation is observed.
In this paper, the absorption and fluorescent spectrum of Tm3+:YVO4 at room temperature were measured. According to Judd-Ofelt theory, the intensity parameters (Omega) (lambda )((Omega) 2 equals 3.166 X 10-20 cm2, (Omega) 4 equals 1.368 X 10-20 cm2, (Omega) 6 equals 0.955 X 10-20 cm2) were worked out. With these values, oscillator strength, spontaneous radiative rate, radiative lifetime, branching ratio and integrated emission cross-section were calculated. The potential application of Tm3+:YVO4 crystal to be a laser material was also discussed.
Additive pulse mode locking (APM) utilizes self-phase modulation in an auxiliary cavity to produce pulse shortening in the main laser by coherent interference at the coupler mirror. The auxiliary cavity viewed as a linear dispersive termination transforms an incident pulse into a reshaped reflected pulse. The laser pulses incident upon and reflecting from the auxiliary cavity add coherently at the mirror. If the length of auxiliary cavity is properly chosen, self-starting APM could be obtained. In this paper, a Fabry-perot APM configuration was used. The pumping source was a 3 W diode array produced by SDL company, the efficiency of the coupling optics was 80%. The Nd:YLF rod was 5 mm by diameter 3 mm, which was plano-Brewster cut along the c-axis. When pumped with the maximum power of 2.4 W (incident upon the media), stable CW mode locked trains of 2 ps pulses are generated at 1.053 micrometer, with an average unstable output power of 76 mW, corresponding to a peak power of 283 W.
We have demonstrated a laser diode pumped Nd:YVO4 laser that produced 273 mW cw output at 671 nm with a KTP crystal as intracavity frequency doubler. The optical-optical conversion efficiency of the all-solid-state red laser was 5.1%.
The experiment of MOPA (Master-Oscillator-Power-Amplifier) laser System with an optical fiber as the phase conjugate mirror is introduced. The output laser beam from the unidirectional ring resonator was amplified and coupled in an optical fiber. We got the phase conjugate beam. When the repetition rate varied from 1 to 30 Hz, the far field divergence varied from 0.6 to 0.9 mrad, and the corresponding M2 is in the range of 1.1 to approximately 1.6.
We demonstrate a femtosecond Kerr-lens mode-locked Cr:LiSGaF laser that based on a compact cavity geometry. For the first time to our knowledge, with a combination of 488-, 476- and 458-nm lines from Argon-ion laser as a pump source, 58-fs pulses centered at 845 nm were generated. The average output power is 30 mW, and the time-band product is 0.331, assuming a sech2 pulse shape. Neither Acousto-modulator nor physical aperture or slit were used in this cavity to start and sustain the Kerr-lens mode-locking operation.
This paper is to introduce the principle and the experimental operation of Q-switching and tuning of flashlamp pumped Ti:Sapphire laser with electro-optic crystal. A LiNbO3 (LN) crystal (13.8 X 14.7 X 46.5 mm3), a quartz quarter wave plate (204 micrometer in thickness), and a Glan prism were inserted in the cavity. Before a Q-switching voltage was applied to the LN crystal, the loss corresponding to quite wide wavelength band was high, the oscillation of the laser was prevented. The Q switching was achieved with the voltage on, different voltage corresponding to different wavelength at which the laser had the highest Q figure. The Q- switching and the tuning of the laser was achieved at the same time in this way.
Some methods are introduced in the paper, to reduce the damage to the detector as the laser power is high as 10 kw. To measure the high-power laser accurately, several couples of pieces having high transmittance, low thermal effect, and low reflectivity are used to measure the high-power laser mode accurately. The beam cutter with a slit of 0.01 mm width is used to measure the high-power beam divergence, and the reflective method is used to measure the high-power laser polarization. Directness, simplicity and effectiveness, are the designed considerations in the paper, as these factors contribute to advancing the instrument's accuracy.
A thermal tube based high power and energy meter is introduced, which uses a thermal tube as an isothermal receiver to realize an upper range of 1 X 106 J by the effective thermal conduction the tube and the elimination of thermal lag, with a total uncertainty (mu) less than 5%. A non- contacting method for measuring the laser off-beam power and energy is also described which can indirectly measure the beam power, energy, peak power, waveform and laser pulse frequency by measuring the off-beam scatter based on the principle of the functional dependence of beam on its scatter. Finally a description of a ceramic attenuation meter for high-peak power and energy is given.
A detailed analysis was carried out for the characteristics of dynamic stability zone of parallel-plane-concave laser cavity on the basis of quantitatively taking account of an equivalent convex lens due to thermal lens effect. It was found that in a special case the parallel-plane-concave cavity can work with only one stability zone, in stead of two stability zones under general circumstances. According to theoretical analysis, we selected a set of cavity parameters by taking Nd:YAG laser as an example and carried out the experiments. The results showed that within a rather wide range of pump power, the output of the laser increased steadily, almost in a lineal way.
Making use of the double doped (Nd, Ce):YAG crystal rod made by south-west Institute of Technical Physical in the compact repetitive solid state laser, the more increasing laser efficiency at the high surrounding temperature (50 degrees Celsius to approximately 140 degrees Celsius) has been found with the codoped crystal laser than that with the usual Nd:YAG crystal laser. The energy transfer mechanism between Ce3+ and Nd3+ was studied at a higher temperature (100 degrees Celsius). The increasing radiative energy transfer was observed at the high surrounding temperature than at the normal room temperature. This means that the radiative energy transfer mechanism between Ce3+ and Nd3+ is much more improved at the higher surrounding temperature than that at the room surrounding temperature.
In laser propagation in the atmosphere, the wavefront of laser beam will be distorted by the atmospheric turbulence. The wavefront aberration can be compensated with the stimulated Brillouin-scattering (SBS) effect. In this paper, an outdoor experiment is presented. In the experiment, a ruby oscillator and an amplifier are used as source; a laser beam travels from the source to a reflector; which simulates a target; the reflected laser beam travels through the atmosphere and is focused into a SBS cell by a lens; finally the phase conjugate light produced by the stimulated Brillouin scattering (SBS) effect return to the target. The distance between the target and the SBS cell is 70 m. The Output energy of the ruby laser is 2 J. The laser beam spot and the phase conjugate light spot are recorded by a camera at the target. The result of the experiment shows that: the wavefront aberration is compensated in the process of laser beam and the phase conjugate light travels between the target and the SBS cell.
A low power optically-pumped FIR laser was installed for supplying frequency standard to FEL. The pumping power of single IR line from a grating turned CO2 laser was below ten watts. The FIR output achieved was unstable. In this paper, sources of instability and their solving methods were reported. In addition, a new design for compact optically- pumped waveguide FIR laser was also introduced. In this design, a traditional CO2 laser envelope was skillfully used as the base frame.
A single simulation model describing the discharge circuitry is introduced. First the differential equations are presented. In order to calculate the laser head discharge current, the thyratron resistance with a switching time coefficient (tau) s is investigated. The plasma conductivity used in these models is estimated using the available data on plasma parameters. Here 0.6 eV of the average electron temperature and 80 nH of thyratron inductance are assumed according to our previous model. The laser head discharge current of the differential equations is calculated with the method of Runge- Kutta. The discharge current profiles of the simulation are found to be in close agreement with the experimental data which come from 4.8-cm-diameter and 6.5-cm-diameter middle- bore Copper-Vapor Laser. In this way, the factors which effect the short rise time to increase lasing ability in the CVL (Copper-Vapor Laser) are studied on the bases of studying the storage capacitor's and the peaking capacitor's effect. As a calculation result, the inductance of the laser head takes an inferior effect to the thyratron circuit inductance on the discharge current rise time. Very good agreement exists between the calculated and measured results. This is a successful single discharge model.
Bound-free vacuum uv emissions were observed from electron- beam-pumped gas mixtures of Xe or Kr with hot alkali vapors. The observed four emission bands were assigned to the 21(Sigma) + yields 1 1(Sigma) + or 11(Pi) yields 11(Sigma) + transitions of the Xe+Cs, Kr+Cs, Xe+Li, and Kr+Li ionic excimers.
In this paper, investigations have been made on a CO2 laser with the quasi-tube-plate discharge electrodes under a new gas flow condition. A theoretical model for calculating the stable operation parameter of the new laser was present. A preliminary calculation on small signal gain under many operation conditions has been made. A stable discharge with the input power density of 20 W/cm3 had been obtained in the experiment.
In order to improve the output beam quality of slab waveguide CO2 lasers, we presented an optical phase-shifting array resonator with a phase-shifting array end mirror used in RF- excited diffusively cooled slab waveguide CO2 lasers. A series of phase-shifting array end mirrors with different parameters are employed in our experiments and highly spatially suppressed single-peak intensity distributions in the far field, which have advantages of high brightness and good characteristics of propagation, have been obtained respectively. Theoretically we analyzed the characteristics of the output mode and well explained the phase coupling of this kind of slab waveguide CO2 lasers.
A kind of reversal shear interferometer has been designed to measure the temporal change of spatial coherence of KrF excimer laser with an unstable resonator. By this method, we can obtain the degree of spatial coherence from a single measurement. At different shear distance, using slit and photodetector we have observed the stepwise increase of the degree of spatial coherence at intervals equal to the transit time of resonator. Moreover, ray matrix has been used to analyze the propagation of partial coherent light and the coherence widths of successive passes are calculated.
The average fluence distribution of excimer laser is an important parameter in various applications of excimer laser. But it is more difficulty to measure the parameter due to UV wavelength of excimer laser, very short pulse width, energy undulation among various pulses and or so. Basing on the anisotropy Seeback tensor coefficients, a light-thermo radiation detector made from high Tc superconductor YBa2Cu3O7-(delta ) was fabricated. The novel advantages of this detector are that it functions at room temperature, with very low noise, very fast response and higher sensitivity within a very wide wavelength from ultraviolet to infrared. A measuring system of average fluence distribution of excimer laser is formed with the YBCO light-thermo-detector, a lock-in amplifier and a computer. The principle of the measurement system is analyzed, XeCl laser fluence distribution is measured.
The copper ion laser supplies interesting CW UV emission in the region 248 - 270 nm. It is possible to realize VUV (-160 nm) laser oscillation in the copper ion laser. Its discharge characteristics, laser gain and output performance in dependence on the operating conditions have been investigated. A UV laser gain of 4.72%/m and a quasi-CW power of 700 mW without the optimum of the output coupling have been measured. The processes in laser plasma can be described and the experimental results were good explained with a theoretical model presented by the author.
In this paper, Xe and He-Ne atomic lasers and CO2 molecular lasers excited by 30 MHz approximately 2 GHz frequency have been studied, and then put forward the key of getting high efficiency is how to control the electron energy of discharge space. In the mobility-dominated discharge space of Xe laser, the product of gas pressure and input power is constant. In He-Ne laser, the product of gas pressure and power supply frequency is a constant in plasma discharge space of the glass tube under the optimum laser output. As to the slab waveguide CO2 laser, the center of discharge space is quasi-Faraday dark region. But to the high power CO2 laser (flow gas) the discharge space is plasma. Since there demand much lower electron energy, and high density for CO2 laser, only in discharge structure there are several designing schemes can be referenced.
We present the numerical results of the dynamics of a single- mode homogeneously broadened CO2 laser system with external optical feedback. Firstly, we introduce the CO2 laser equations in which we added the team of optical feedback into the two-level single-mode CO2 laser equations. Secondly, the stability of the equations was analyzed and the equations was solved numerically. We find a little amount of optical feedback will induce the system from steady state to unsteady state and with the feedback increasing the system become periodic, quasiperiodic and finally chaotic states. The delay time will also affect the system stability. Lastly, the attractors and the power spectra of this system were given.
The medium refractive index in a high-power laser resonator will vary with the radial variation of the physical quantities such as the temperature, the pressure, the current and energy, and its distribution is something of a lens-like one. As a result, the oscillation performance of the laser will be changed and the aberration of the lens-like medium will occur. According to the ray matrix theory, with a telescopic confocal unstable resonator as an example, the effect of lens-like medium in the laser resonator and its aberration correction is analyzed with the geometric method. It is pointed out that this kind of aberrations can be effectively corrected with the method proposed.
By means of mirror, the small signal gain coefficients of the third continuum of argon pumped by relativistic electron beam are measured. According to the experimental setup, an accurate mathematical model about detection in close range is built. With numerical method, the model is calculated by computer and the small signal gain coefficients of the third continuum are obtained. This is the first report about the small signal gain coefficients of the third continuum of argon.
A multikilowatts supersonic chemical oxygen iodine laser has been constructed. An output power of 7.1 kw with chemical efficiency 20.3% has been achieved. The beam quality of (beta) less than 2 were achieved on unstable resonator with beam rotation. The diagnoses of spectral characteristic, 2 dimension small-signal gains and water vapor measurement etc. have been studied.
A two-dimensional program was applied to simulate the chemical dynamic process, gas dynamic process and lasing process of a combustion-driven CW HF overtone chemical lasers. Some important parameters in the cavity were obtained. The calculated results included HF molecule concentration on each vibration energy level while lasing, averaged pressure and temperature, zero power gain coefficient of each spectral line, laser spectrum, the averaged laser intensity, output power, chemical efficiency and the length of lasing zone.
Rare earth fluoride YbF3 has been investigated as possible substitute materials for standard thorium fluoride layers in infrared laser optical components. All dielectric multilayer high reflective coatings with 3.8 micrometer and 0.6328 micrometer two wavelengths consisting of alternative ZnS and YbF3 materials are presented in this paper. The deposition process and physical properties of YbF3 coating have been studied. The performance measurements and damaged thresholds of the reflector are reported at .3.8 micrometer.
Propagation of optical field through an optical system characterized by an ABCD ray matrix has been investigated in the spatial frequency domain. The behavior of the angular spectrum of the optical field can be directly obtained by use of the diffraction integral in spatial frequency domain which has been derived by this paper. Some examples have shown that for some problems it is more convenient to study in frequency domain by using the frequency-domain diffraction integral formula than in spatial domain.
An electromagnetic-wave-wiggler free electron laser with a tapered axial guide magnetic field is proposed. A three- dimension self-consistent nonlinear simulation program about electromagnetic-wave-wiggler free electron laser is also developed. Both the scattered wave and the pump wave are considered to be disperse in the program. A set of coupled nonlinear differential equations is derived which governs the self-consistent evolution of either TE or TM modes in a loss- free cylindrical waveguide. The energy exchange of the electron beam with the pump wave and the scattered wave are fully taken into account. The simulation result of the output power for an untapered guide magnetic field is in agreement with the reported result in experiment. By using the simulation program, the electromagnetic-wave-wiggler free- electron laser with a tapered axial guide magnetic field is discussed. The results show that, compared to an untapered guide magnetic field, a tapered guide magnetic field can enhance the output power. However, the enhancement is related to the slope and the starting position of the taper of the guide magnetic field.
The dye-doped silica slab was fabricated by sol-gel method. Under transverse pumping by a XeCl laser (308 nm), narrow-band (3 nm) laser oscillator from Exalite 376 (E376)-doped silica slab was achieved in an echelle grating resonator cavity. The efficiency of the silica slab can be up to 2.5%.
In this paper, we report analytical and experimental studies on the characteristics of a high-brightness LD end-pumped Nd:YVO4/KTP laser. A simple model was developed to optimize the cavity parameters and estimate the green output power of intracavity frequency doubled lasers. Using a 1 W high brightness laser diode as the pump source, high efficiency operation was realized based on optimized cavity design. The second-harmonic output power at 532 nm was measured to be 286.5 mW at an incident pump power of 881.4 mW, corresponding to an optical to optical efficiency of 32.5%.
A pulsed Nd:YVO4 mini disc laser pumped by a laser diode array is reported in this paper based on the end-pumping configuration with the linear plane-parallel cavity and the V- folded cavities respectively. The input-output properties and the output beam are characterized, analyzed and compared. The optical-to-optical conversion efficiency is about 51% for the plane-parallel cavity, 48% for the V-folded plane-plane cavity and high up to 68% for the V-folded concave-plane cavity. The V-folded cavities offer good TEM00 mode while the linear plane-parallel cavity operates in a multi-mode statue.
In this paper, we present the experimental results obtained with Tm:YVO4 and Tm,Ho:YLF active medium pumped in an active mirror configuration. Optical to optical efficiency, beam quality and spectral characteristics obtained for both crystals are compared. Extensive research is being devoted to the development of solid state lasers emitting in the eye safe spectral range with the possibility of efficient diode-pumped sources. There is a promising range of applications foreseen for such devices including LIDAR, metrology and medical applications. The microchip concept, where the mirrors are coated directly on the crystal faces polished parallel, allows to set up in very compact sources with high spatial quality beams. Resulting from the compactness of the cavity, these lasers are very stable. We present in this paper the results obtained in our laboratory for both Tm:YVO4 and Tm,Ho:YLF microchip lasers.
Phase coupling of medium power high beam quality lasers are of great interest for achieving high power diffraction limited beam with high gain lasers. This make it possible to set up compact and efficient sources. In this paper, we review the work performed in our laboratory concerning the coherent array of CO2 waveguide lasers. We report the various techniques used for phase coupling like Talbot effect, intra-cavity spatial filtering and anti-guiding effect and we give the relevant performances in terms of beam quality and efficiency. After, we discuss the advantages and drawbacks brought by each one. The far field diffraction pattern supplied by a series of coherent independent lasers is made of several asymmetric lobes. We then present lossless techniques making it possible to convert this multilobe asymmetric far field diffraction patterns into a single lobe symmetric beam. Last, we discuss the capability of slab CO2 laser with a graded-phase mirror cavity for generating large stable mode and, then, improving the energy extraction efficiency.
We have developed phase conjugators consisting of multimode fused silica fibers in standard or tapered geometry with core diameters between 25 and 400 micrometer. Such optimized fiber phase conjugators operate with more than 50% reflectivity, 93% fidelity, and less than 200 W threshold in the wavelength range from infrared down to the ultraviolet. A depolarization of SBS pulses could be reduced to less than 0.3% by proper configuration of the fiber. High power densities of more than 1 GW/cm2 do not damage our fiber phase conjugators, because the absorption of the fiber materials used is very low. Furthermore, fiber phase conjugators are harmless to the environment and beat the performance of dangerous liquid or high pressure gas SBS-cells used in high power lasers up to now in all concerns. High economic benefits can be expected due to the popular fiber materials used from the glass fiber technology. New applications of fiber phase conjugators in high power lasers with different architectures and at an average output power of more than 100 W have been demonstrated. Versatile new aspects with this novel adaptive optics for potential applications in high power lasers is summarized.
Multimode quartz fibers based on stimulated Brillouin- scattering (SBS) are effective phase conjugators in a broad wavelength range from the near infrared over the visible down to the near ultraviolet, offering a good alternative to fluid and gaseous SBS-media that are toxic or operated under high pressure. In our previous investigations of fiber phase conjugators, a saturation of the SBS reflectivity was observed at values between 50 and 60%, not considering the reflection losses at the fiber surface. To understand this saturation phenomenon, the SBS-reflectivity in undoped multimode quartz fibers of different geometries was measured with temporal and spectral resolution. Second order SBS could not be observed in the interference ring pattern of the transmitted pulse. The temporal modulation of the reflected and transmitted light increased with the input laser power and the incident laser pulse length and also when a tapered fiber was used. Such oscillations of the power of the reflected pulse could explain the saturation behavior of the total SBS reflectivity of fiber phase conjugators to some extent. Also the recent observation of a decreased effective interaction length in multimode fibers at high pump power could give new clue to the origin of such a saturated SBS reflectivity.
An F2+ color center laser operation has been performed using a two-mirror cavity at room temperature by photo-ionizing of the F2 color centers in LiF crystal. The ionization was undertaken with the 532 nm second harmonic radiation of pulsed Nd3+-doped YAG laser. We observed the F2+ broadband (i.e. free-running mode) laser oscillation with a peak at 930 nm and compared with the broadband LiF:F3+ color center laser oscillation.
This paper reviews and discusses the performance of unstable resonators concentrating on the design, analysis, and test of oscillators used on electric discharge laser devices. The work covers over 15 years of pulsed CO2 laser device development. The emphasis is on the review of the energy extraction and beam quality experimental results from a wide range of devices. The effect of flow characteristics on laser performance is discussed. The interaction between the optical mode formation and the laser medium, called the 'Mode-Medium Interaction,' is presented. The device design constraints imposed by optical material limitations is also discussed.