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The edge effects of high-power slab lasers cause severe wavefront distortions with large amplitude and gradients, which is a great challenge for the adaptive optics systems for improving the beam qualities. The standard least-squares wavefront reconstruction method would inherently assign higher priorities to correcting the edge aberrations which contribute little to the laser power in the near diffraction-limit areas in the far-field, while the other aberrations are not well corrected. To solve the problems, we propose a least-squares reconstruction algorithm with performance-based filtering, in which the correction capability of the deformable mirror is analyzed in the spatial frequency domain, and then the input phase distortions are filtered accordingly. The uncorrectable components of input distortions are ignored so that the residuals of the correctable components could be further minimized. Experiments with a 20 kW Nd:YAG slab laser indicate that the proposed method is effective to improve the beam quality of high-power slab laser with edge effect.

A passively Q-switched Ho,Pr:LiLuF4 laser at $2.95~\mu \text{m}$ was demonstrated by using a MoS2 saturable absorber, which was prepared by a liquid phase exfoliation method. Under an absorbed pump power of 3.77 W, the maximum average output power of 70 mW was obtained with a repetition of 85.8 kHz and a pulse duration of 621 ns. The results reveal that Ho3+/Pr3+-codoped LiLuF4crystal is a promising candidate to generate 3- $\mu \text{m}$ pulsed laser.

We demonstrate a laser-diode-pumped Nd:YAG slab amplifier with dimensions of 7×35×138.2 mm. The fluorescence is homogeneously distributed in the Nd:YAG amplifier, and a stored energy of 3.2 J can be achieved at 1,500 W pump power. For a repetition frequency of 200 Hz, 25 μJ injection polarized seed light, and 1,500 W pump power, the small signal gain reaches 12.66. At the same repetition frequency, 0.4 mJ with 27 ns bandwidth of injected seed-light energy and a 6×26 mm aperture, the output energy reaches 1.071 J. The extraction efficiency is 33.46% after four-pass amplification. An energy amplification from millijoules to joules is realized for the injected laser beam.

We demonstrated a high power and good beam quality continuous-wave (CW) Tm:YAP slab laser operating at room temperature. Two fiber-coupled laser diodes were used as pump source, the maximum output power of 105 W at 1936.4 nm was achieved with the total incident pump power of 308 W, corresponding to the slope efficiency and optical-to-optical efficiency were 41.4% and 34.1% with respect to the incident pump power, respectively. At the maximum output power, the beam quality factors M2 were 2.76 and 2.78 in the x and y directions, respectively. Besides, a theoretical model was presented to predict the temperature distribution, thermal induced stress and laser performance of the Tm:YAP slab laser, and the experimental results were consistent with the theoretical simulation results which indicated that this model could simulate hundred-watt-level Tm:YAP lasers well.

For a high-power slab solid-state laser, obtaining high output power and high output beam quality are the most important indicators. Adaptive optics systems can significantly improve beam qualities by compensating for the phase distortions of the laser beams. In this paper, we developed an improved algorithm called Adaptive Gradient Estimation Stochastic Parallel Gradient Descent (AGESPGD) algorithm for beam cleanup of a solid-state laser. A second-order gradient of the search point was introduced to modify the gradient estimation, and it was introduced with the adaptive gain coefficient method into the classical Stochastic Parallel Gradient Descent (SPGD) algorithm. The improved algorithm accelerates the search for convergence and prevents it from falling into a local extremum. Simulation and experimental results show that this method reduces the number of iterations by 40%, and the algorithm stability is also improved compared with the original SPGD method.

A temperature insensitive all solid state laser functioning from −30°C to 50°C without cooling facility is realized. Maximum output pulse energy about 95mJ is obtained over above temperature range.

We present a design and analysis for the surface gain medium slab laser. This single slab laser is potential to output 12kW class laser. The experiment already achieved 5kW CW laser power output.

We report on a hundred-watts-level high power Tm:YAG slab laser system operating at room temperature. The laser has a threshold pump power of 46.7 W, benefiting from the good mode matching of an end-pumping scheme and the excellent heat-dissipation capability of our cooling system. At 350 W of incident pump power, 100 W of output power at ∼2015 nm has been generated, corresponding to a slope efficiency of 33.6% with respect to the incident pump power and an optical-to-optical conversion efficiency of 28.6%. As far as we know, this is the highest optical-to-optical conversion efficiency so far achieved in a high power Tm:YAG laser system operating at a hundred-watts level.

Adaptive optics is an important technology for improving beam quality in solid-state slab lasers. However, there are uncorrectable aberrations in partial areas of the beam. In the criterion of the conventional least-squares reconstruction method, it makes the zones with small aberrations nonsensitive and hinders this zone from being further corrected. In this paper, a weighted least-squares reconstruction method is proposed to improve the relative sensitivity of zones with small aberrations and to further improve beam quality. Relatively small weights are applied to the zones with large residual aberrations. Comparisons of results show that peak intensity in the far field improved from 1242 analog digital units (ADU) to 2248 ADU, and beam quality β improved from 2.5 to 2.0. This indicates the weighted least-squares method has better performance than the least-squares reconstruction method when there are large zonal uncorrectable aberrations in the slab laser system.

We present a PPMgOLN optical parametric oscillator pumped by approximate uniform rectangular distribution. Output power of 191.8 W for both the 1.68 μm signal and 2.89 μm idler lasers and 53.2% conversion efficiency were achieved.

A laser-plasma source comprising a rotating cryogenic solid-state Xe target has been studied for use in extreme ultraviolet lithography (EUVL) systems equipped with La/B4C mirrors. The laser-to-EUV power conversion efficiency (CE) of the cryogenic Xe target was improved to achieve a maximum CE of 0.15 % at 6.7 nm with 0.6 % bandwidth. We successfully demonstrated the continuous generation of EUV light with an average power of 80 mW at 6.7 nm with 0.6 % bandwidth using a Nd:YAG slab laser at a repetition rate of 320 Hz and an average power of 100 W. Scaling-up of the laser-plasma source for use as a future EUVL source is also discussed.

We report a high power zigzag slab laser oscillator employing two composite Nd:YAG/YAG slab in the cavity. The CW laser output with the power of 401 W was achieved from the oscillator with the optical-optical efficiency of 32.6%. The beam quality is estimated as M x 2 ≈ 10, M y 2 ∼ 50 in the slab width and thickness direction, respectively.

We demonstrate a high-efficiency and high-power quasi-three-level laser based on a trapezoidal composite slab architecture with a 270 μm-thick Yb-doping surface. The design of a surface-doped slab architecture, temperature effects, laser oscillator model, and laser oscillator experiments with a surface-doped slab as a laser host medium have been presented. By theoretical calculation, the temperature rise in the surface-doped slab is only one seventh of that in the bulk-doped slab at the same maximum pump power of 30 kW. Finally, in the laser oscillator experiments, an output energy of 21.6 J is obtained when the pump energy is 48 J with a repetition rate of 5 Hz and a pulse width of 1 ms. The optical-optical efficiency is 45%.

High efficient CW lasers at 1064 nm and 1342 nm were realized in a compact diode-end-pumped Nd:YVO4 slab. The maximum 1064 nm output power of 22.5 W was obtained under the pump power of 56.0 W, corresponding to the maximum optical conversion efficiency and slop efficiency of 40.1% and 50.1%, respectively. When the pump power was 34.7 W, the maximum output power at 1342 nm was obtained to be 4.4 W. The corresponding slope efficiency and the optical conversion efficiency were 17.9% and 12.6%, respectively.

The thermal properties of the grazing-incidence slab laser are investigated when cooling with a novel composite method, both conducted cooling and air cooling. The 3D temperature distribution and the correspondent thermal lensing effect were analytically modeled and numerically calculated. The absorption saturation and stress-optic effect were taken into account in the modeling. The influence of the parameters of the laser on the thermal lensing effect were investigated in detail. The results show a lower temperature and weaker thermal lensing effect for the composite cooling than for the traditional contaction cooling.

In this paper, we present a laser-diode (LD) bar end-pumped Nd:YVO4 slab laser, which uses a simple coupling system and a compact quasi-concentric resonator (QCR). A TEM00 output was obtained with a pump width varied from 2.57 to 9.44 mm and the slope efficiency is kept at about 48%. Under 40-W pumping, a maximum TEM00 output of 15.84 W was achieved and the optical-to-optical efficiency was 39.6% correspondingly.

We demonstrate optimization of passively Q-switched Yb:LuAG laser. Pulse energy of 10.1 mJ corresponding to peak power of 2.5 MW was achieved. Above 100 mJ with 23% efficiency in free-running operation was obtained.

A new set of asymmetric modes was recently revealed in a Xe slab laser with pronounced lens effects originating from gas heating in the discharge. The appearance of these modes is a threshold effect. Their domain of existence in the Xe laser is discussed. It is shown that mode competition can result in output radiation asymmetry. Theoretical results are compared with experimental data.

A high average and high peak brightness Nd:YAG MOPA laser system composed of a laser-diode-pumped Nd:YAG master oscillator, flash-lamp-pumped slab power amplifiers and a phase conjugated mirror was developed. The system demonstrates an average output power of 235 W at a repetition rate of 320 Hz and a peak power of 30 MW at a pulse duration of 24 ns with M/sup 2/=1.5. Both an average brightness of 7/spl times/10/sup 9/ W/cm/sup 2//spl middot/sr and a peak brightness of 1/spl times/10/sup 15/ W/cm2/spl middot/sr are achieved simultaneously. The system design rules that we confirmed suggest that by replacing lamp pumping in the amplifier with laser-diode pumping, an average output power of /spl sim/1 kW can be obtained at /spl sim/1 kHz with a higher average brightness of /spl sim/3/spl times/10/sup 10/ W/cm/sup 2//spl middot/sr and a higher peak brightness of /spl sim/3/spl times/10/sup 15/ W/cm/sup 2//spl middot/sr.

43.6 W near-diffraction-limited continuous-wave laser beam at 1342 nm in 880 nm laser-diode partially end-pumped Nd:YVO4 slab laser is presented. The slope efficiency and optical-to-optical efficiency with respect to absorbed pumping power were 45.4% and 35.9%, respectively. At output power of 34.5 W, the M2 factors in unstable and stable directions were 1.3 and 1.2, respectively.

The reflectance and transmittance of an etalon have been derived for a partially coherent incoming beam. A method of enhancing the pumping of a slab laser crystal has been considered and investigated theoretically. If the pumping laser has a coherence length that is about five times the slab crystal thickness, Fabry-Perot effects can be efficiently utilized to optimize the absorption in the crystal. Examples for different coherence lengths have been computed. Furthermore, designs of the coatings on the front and end faces of the slab crystal are given.

We conduct a comprehensive investigation of the lasing mechanism in a photonic crystal slab laser with a refractive index that is periodic in two dimensions. Experimental spectra of laser structures fabricated with organic gain media are presented. It is found that lasing frequencies can be explained in terms of Van Hove singularities in the density of modes. We also observe lasing spectra that cannot be obtained from structures with one-dimensional periodicity, such as traditional distributed feedback lasers. Lasing frequencies are computed using numerical techniques.

High repetition rate (320 pps), high average power (100 W) pulse Nd:YAG slab laser has been developed for x-ray driver. A strong X-ray emission around 10.8 nm, which wavelength is attractive for x-ray projection lithography, was generated from cryogenic Xe targets pumped by this laser pulses. CO 2 and H 2 O were also tested for cryogenic targets and we found that the emission intensity from Xe around this wavelength region was at least 10 times higher than that from H 2 O, CO 2 .

A novel side-pumped structure with microlens-free diode arrays and a lensduct was demonstrated. This structure is much more robust and simple than traditional approach of a microlens-conditioned diode arrays with a lensduct. A quasi-CW diode arrays side-pumped KD*P Q-switched Yb:YAG slab laser has been demonstrated. An output energy of ∼10 mJ/pulse with pulse width as short as ∼20ns is obtained at 1–10 Hz repetition rate. To our knowledge, this is the shortest pulse width of Electro-optic Q-switched laser output by using Yb:YAG as the gain medium.

A novel concept of corner pumping has been developed. The corner-pumped slab design allows long absorption length and symmetric conduction cooling, making it particularly suitable for high-power quasi-three-level lasers. A corner-pumped Yb:YAG slab laser has been demonstrated for the first time. A preliminary experimental result shows that the laser produces 202 W of cw output power with 1400 W of incident pump power.

The performance of a flash-lamp pumped Cr/sup 3+/: LiSrAlF/sub 6/ multi-bounce slab laser is reported. The slab was conductively-cooled by a sapphire window which also transmitted the pump light. Laser output of 9 mJ and a slope efficiency of 0.061% were obtained although less than 15% of the total pump aperture was used. >

A novel distributed-side-pumped configuration is presented for power scaling of solid-state slab lasers, which combines the advantages of both end-pumped and side-pumped geometries, realizing large absorption length and large pump area at the same time. In the distributed-side-pumped slab laser, the long gain medium can be divided into multiple segments (slab units), each of which adopts an end-pumped like geometry, thus the pump uniformity and the utilization ratio of the whole slab are greatly improved comparing to the end-pumped scheme. Furthermore, this configuration decouples the pump windows from the cooling areas, avoiding the necessity of water sealing the optical surfaces. The parameters of gain medium and pumping system are carefully optimized, while numerical calculation of thermal effects for composite slab and homogeneous slab are compared. An oscillator based the Nd:YAG slab that includes 5 slab units, is expected to produce CW output at 1 kW level, with the optical-optical efficiency of 52.6%. By adding more slab units, the distributed-side-pumped slab laser can be enhanced easily and efficiently.

An 80 W Tm:YLF Volume Bragg Grating laser selected to operate at 1890 nm is demonstrated. It consisted of a single Tm:YLF slab pumped with a 300 W diode stack using a pump reproducing configuration.

Chirped-pulse amplification of picosecond pulses is demonstrated in a compact Nd: glass laser system. A Nd: phosphate glass slab laser is used to produce terawatt pulses as a power amplifier. The detailed characterization of the zigzag slab amplifier is described. The laser system produces > 1 J, 1.0 ps pulses at a 1 Hz repetition rate.

A single-frequency single-pass amplifier based on Ho:YLF and Ho:LuLF in a scalable slab architecture delivering up to 210 mJ at 2064 nm is demonstrated. The amplifier was end-pumped by a 1890 nm Tm:YLF slab laser and was seeded with a 69 mJ single-frequency Ho:YLF ring laser operating at 50 Hz.

By using of computer simulation, a novel numerical method of astigmatism compensation for intracavity-double-frequency slab laser is introduced, which overcomes the astigmatism compensation disadvantage, such as, loss of efficiency or improvement of the processing cost to improve the beam quality. This method is simple, precise and easy to operate.

We report a diode face-pumped, face-cooled, Er:YAG slab cryo-oscillator producing 420W quasi-cw at 50% duty-cycle and 386W cw near 1645nm with 0.16nm linewidth, believed to be the highest average power reported for any Er:YAG laser.

Based on ununiformity of stored energy in laser gain medium due to the lower absorbed pump energy distribution uniformity in reality, the effective fill factor f (2 − f) of Frantz-Nodvik(F-N)Equation for Zig-zag Optical Path Slab Laser Amplifiers is modified by using the absorbed pump energy density.

Recently, there has been an increased interest in high-power and high-energy 2-µm lasers, due to a number of potential medical, military and scientific applications. Our aim is to develop a high-power Tm:YLF slab laser which can be utilized to pump a Ho slab laser. A 68 W Tm:YLF slab laser was recently presented in [1] pumped from one end by a single 6-bar stack delivering ∼300 W of pump power. In this work, we present a Tm:YLF slab laser pumped by two diode-bar stacks from both ends, leading to a maximum output power of 192.5 W.

Design and characterization of the YAG:Nd 3+ slab geometry laser with an on-axis positive branch unstable-unstable resonator is described and discussed in the paper.

A novel scheme of fully immersing water cooling is proposed for a Nd:glass radial slab laser. The slab medium is entirely immersed in the circulating water filling the pumping cavity, which enables much lower temperature and reasonably smaller thermal gradient in the slab medium. The radial slab is symmetrically and synchronously pumped by eight flash lamps, and produces multi-output beams with a total energy of 469 mJ. Incoherent beam combination property of the multi-output beams is also investigated. The approach suggested here provides a way of scaling the slab lasers to much higher output levels and also a convenience for beam combinations.

Laser diode-end-pumped Nd:YVO4 slab laser with a hybrid resonator operating at 1064 nm was carried out. The size of Nd:YVO4 crystal with 0.3 at.% doped concentration was 14 mm × 10 mm × 1 mm, which was cut along the a axis and the c axis was parallel with the 14 mm direction. By using a compact negative confocal unstable-stable hybrid resonator, 134 W 1064 nm laser output was realized with the M2 factors in the unstable direction and in the stable direction were 2.1 and 1.7 respectively. The slope efficiency and optical-to-optical efficiency were 49.3% and 40.2%, respectively.

We studied numerically and experimentally the effects of structural disorder on the performance of ultraviolet photonic crystal slab lasers. Optical gain selectively amplifies the high-quality modes of the passive system. For these modes, the in-plane and out-of-plane leakage rates may be automatically balanced in the presence of disorder. The spontaneous optimization of in-plane and out-of-plane confinement of light in a photonic crystal slab may lead to a reduction of the lasing threshold., 5 pages, 5 figures

We present an experimental study of a continuous-wave Nd:YVO4 laser diode-pumped directly in band at 880 nm. By using a compact positive confocal unstable-stable hybrid resonator, a maximal laser output of 170 W at 1064 nm is realized. The slope efficiency and optical-to-optical efficiency are 56.7% and 51.3%, respectively. The M2 factors in the unstable direction and in the stable direction they are 1.9 and 1.3, respectively.

We have proposed and designed a diode-pumped solid-state laser (DPSSL) driver for inertial fusion energy (IFE) which consists of water-cooled zig-zag path Nd:glass slab amplifiers. A driver module has 10 kJ total output energy at 351 nm and operates at 12 Hz with 10.4 percent overall efficiency. The laser driver producing 4 MJ blue output for IFE will consists of 400 modules. To confirm the design, we are developing a small scale DPSSL module of 10J X 10Hz laser output at 1053 nm.

Efficient, high repetition rate, Q-switched, TEM00 lasers of mJ level of output energy are required in several applications as: range finding, altimetry, generators for high power systems, technological processes etc. One of the best types of such sources are low energy, solid state lasers pumped by quasi-cw diode laser bars. There were demonstrated several types of such lasers working in end pumped [1 – 4] or side pumped [5 – 7] configurations. The best results in free-running mode namely more than 5 mJ and over 50% efficiency was demonstrated in end pumped Nd:YV04 laser [3]. End pumped laser, generating TEM00 output beam, requires complicated beam shaping optics, moreover thermally induced birefringence diminishes efficiency of electrooptical Q-switching in this case. Side pumped lasers with rod active media suffer from bad beam quality, although due to their scalability they are the best choice in case of high output energy requirements.

The conceptual characteristics of a solid-state laser architecture that promises to provide appropriate characteristics for high average power (MW scale) solid-state lasers, such as those desired for Inertial Fusion Energy (IFE) applications, was first outlined in the early 1980's by J. Emmett, B. Krupke, and J. Trenholme.¹ This design employed a solid-state gain medium that was optically pumped and extracted as well as gas-cooled through the large aperture of a slab. Experimental work was then pursued several years later, when Albrecht, Sutton and co-workers explored this new strategy for cooling solid-state amplifier-slabs with resistive-electrical surface heaters.² Yb:Sr5(PO4)3F (Yb:S-FAP) was discovered and found to be an efficient energy storage gain media and to possess other properties well-suited to a high efficiency rep-rated operation.³ The emergence of high power diode arrays provided the final ingredient needed to build an efficient gas-cooled-slab (GCS) diode-pumped solid-state laser (DPSSL). Orth and co-workers conceptually assembled these advances to describe the potential performance of a MJ scale GCS DPSSL within the laser-driven fusion-energy context.4 A Yb:S-FAP DPSSL was previously demonstrated that had 12% electrical to optical slope efficiencies without the complications of active cooling.5 We report here the first results for a gas-cooled-slab laser device.

Glass laser is the best one to radiate high-average power used for material processing and X- ray production. However, the thermal conductivity of laser glass is very low compared with other laser crystals. We report newly developed glass slab laser operating at 8 Hz without laser glass breakage, the geometrical shape of the glass slab is different from conventional ones. Our glass slab is composed of small square glasses. Slab laser (10 t mm X 40 w mm X 125 l mm) at pumping power of 1500 W emitted the average output power of 46 W.

Coherent beam combining (CBC) is an efficient way to scale the brightness of laser arrays. We demonstrate the active phase locking CBC of two slab laser amplifiers based on the multi-dithering technique. The experimental investigation on the 102 W coherent beam combining of two slab amplifiers shows that the whole system in a closed loop performs well over a long time observation. The contrast of the coherent combined beam profile is about 87% and the combining efficiency is nearly 85%. In addition, the CBC of two green lasers is realized based on the second-harmonic generation of the phase locking pump lasers. To the best of our knowledge, this is the first report about second-harmonic active phase locking, which indicates further potential applications of CBC.

The thermal conduction theory based on uniform heating in the slab laser has been presented before, but results from the theory are very different from the results of experiments. In this paper, a non-uniform heating model based on the absorption law of the medium is proposed. According to the model, the temperature distribution in the slab laser under CW and pulse pumping is solved. Thermal stress and fracture limitation of the slab are given. The new model is in good accordance with the experimental results.

It is well known that improving laser crystal properties is of importance for the laser applications. Recently, a new laser crystal, i.e., YAG doped with Nd+3 and Ce+3 ions has been developed in China. In this paper we report our experimental results with (Nd,Ce):YAG laser including rod and slab laser performance, and Q-switched operation characteristics.

The total-internal-reflection, face-pumped solid state laser (or, simply, the slab laser) has been under development for nearly two decades, since it was first demonstrated by Chernoch and Martin at General Electric [1]. Much of the development has concentrated on the demonstration of systems with near-diffraction-limited performance, which in principal is more readily achieved with the slab laser than with conventional rod-geometry configurations. As Danilov et al have pointed out [2], most of the slab lasers described to date have had considerably lower efficiencies than rod lasers, often the result of pumping-cavity designs chosen for a high uniformity of illumination over the slab surface.