The Diode Array Pumped Kilowatt Laser (DAPKL) has demonstrated more than an order of magnitude increase in brightness and average power for short pulse diode-pumped solid-state lasers since its inception in 1991. Significant advances in component technology has been demonstrated, including development of a diffusion bonding process for producing large slabs of Nd:YAG laser material. Phase conjugation by stimulated Brillouin scattering has been demonstrated with high reflectivity and fidelity in a simple focused geometry with input powers of 100 W. Pulse energies at 1.06 μm of up to 10 J per pulse have been demonstrated with a beam quality of 1.25 times diffraction limited at 33 Hz. An average power of 940 Watts at 100 Hz has been obtained with two times diffraction limited beam quality. Efficient frequency doubling with an average power of 165 W has been demonstrated with 5 J per pulse at 0.53 μm. The system has been packaged in a compact brassboard for long term stability and reliability of operation.

High average output power in conjunction with high beam quality is a crucial point for future industrial applications of solid state lasers. Phase conjugation based on stimulated Brillouin scattering in multi amplifier systems results in average output powers up to the kW-range with high beam quality. A solid state laser system containing six amplifiers and a master oscillator was developed. The system consists of a parallel arrangement of two double pass amplification stages with phase conjugating mirrors. To increase the average output power, both beams are amplified in additional single pass amplifiers again and combined using a thin film polarizer. Optical systems between the amplifiers guarantee the variability of average pumping power without damage of optical components. Therefore the average output power can be tuned between 50 W and 520 W. The beam quality was measured using the moving edge method and corrected for the second momentum of the laser beam. The beam quality is 1.8 times the diffraction limit at minimum pumping power and 5.2 times the diffraction limit at 85% of maximum pumping power.

Long life, high power and high repetition frequency 2D laser diode (LD) arrays are needed for pumping solid state lasers. The reliability of AlGaAs/GaAs high-power lasers has been studied. Over 1 X 10⁹ operation shots in 4-stack 2D LD arrays with 350 W peak output power and over 1 X 10¹³ shots in single-stripe laser diodes with 2.3 W peak output power have been obtained. 2D LD arrays of 3.5 kW (emitting area 3.2 cm x 1.0 cm), 2.5 kW (emitting area 1.0 cm x 1.0 cm) and 2.2 kW (emitting area 6.5 cm x 0.12 cm) were demonstrated under quasi continuous wave operation.

Current work on the Polaroid double-clad fiber laser is discussed. Experiments towards testing the upper power limits of fiber lasers are described. Models for the laser output in the rate-equation approximation, for the laser polarization state, and for the axial-mode-beating noise are presented and compared to experiment.

A novel laser architecture of laser-diode pumped eight pass 1064-nm Nd:YAG zig-zag slab laser amplifier was developed aiming to achieve high energy extraction efficiency and good beam quality. A high energy extraction efficiency of up to 73% for the laser mode volume has been achieved in this amplifier operating at an initial small signal gain of 3.36. The excellent beam quality factor M² of 1.2 has been obtained. The compensation of thermal birefringence in this amplifier was successfully performed.

We compare the effectiveness of various laser systems for producing a sodium guidestar in the mesosphere for large aperture telescopes. We discuss the requirements for two applications at two sites: satellite imaging at the Starfire Optical Range in Albuquerque, New Mexico (SI) and infrared astronomy at the Steward Observatory in Tucson, Arizona (IR). SI may use either a hybrid system employing a rayleigh and a sodium guidestar or a system employing only a sodium guidestar. IR will use only a sodium guide star. Our results are based on analysis and computation that have been compared to 5 different experiments. Parameters included in our comparison are pulse format, polarization, center frequency, and bandwidth. The infrared astronomy application power requirements are low enough that state of the art laser technology can meet them. But the satellite imaging application is problematic. Required powers are sufficiently high that thermo-optic effects in materials can be a problem.

The multi-pass amplifier (MPA) is the last subsystem of the NIF preamplifier, which feeds the main amplification stages of the NIF beamline. The MPA is based on a flashlamp pumped 5-cm diameter by 48 cm long Nd:glass rod amplifier operated at a single pass small signal gain of 15 to 17. The MPA is an off-axis multi-pass image relayed system, which uses two gain isolating image relaying telescopes and passive polarization switching using a Faraday rotator to output the pulse. We describe the MPA system, techniques used to avoid parasitic oscillation at high gain, and suppression of pencil beams. The system is used to generate a well- conditioned 22-joule output from one millijoule input. The output pulse requirements include 22 joules in a square, flat topped beam, and with near field spatial contrast of <5% RMS, square pulse temporal distortion <2.3, and an RMS energy stability of <3%. All of these requirements have been exceeded. The largest impediment to successful operation was overcoming parasitic oscillation. Sources of oscillation could be generally divided into two categories: those due to birefringence, which compromised the polarization contrast of the system; and those due to unwanted reflections from optical surfaces. Baffling in the vacuum spatial filters helps to control the system sensitivity to unwanted stray reflections from flat AR coated surfaces. Stress birefringence in the rather large glass volume of the rod (942 cm³) and the four vacuum loaded lenses are significant, as each of these elements is double passed between each polarizing beam splitter pass. This lowers the polarization contrast of the system, which can prevent the system from operating at sufficient gain. Careful analysis and layout of the MPA architecture has allowed us to address the challenges posed by a system small signal gain of ≈ 33000 and with an output pulse of as high as 27 joules.

The engineering process of integrating the Petawatt (10¹⁵ watts) laser system into the existing 30 kJ (UV) Nova laser at Lawrence Livermore National Laboratory is described in detail. The nanosecond-long, chirped Petawatt laser pulse is initially generated in a separate master oscillator room and then injected into one of Nova's 10 beamlines. There, the pulse is further amplified and enlarged to ~ Φ60 cm, temporally compressed under vacuum to <500 fs using large diameter diffraction gratings, and then finally focused onto targets using a parabolic mirror. The major Petawatt components are physically large which created many significant engineering challenges in design, installation and implementation. These include the diffraction gratings and mirrors, vacuum compressor chamber, target chamber, and parabolic focusing mirror. Other Petawatt system components were also technically challenging and include: an injection beamline, transport spatial filters, laser diagnostics, alignment components, motor controls, interlocks, timing and synchronization systems, support structures, and vacuum systems. The entire Petawatt laser system was designed, fabricated, installed, and activated while the Nova laser continued its normal two-shift operation. This process required careful engineering and detailed planning to prevent experimental downtime and to complete the project on schedule.

Installing the thousands of optics that make up the laser for the National Ignition Facility is a complex operation. This paper introduces the Optical Transport and Material Handling designs that will be used to deliver the optics. The transport and handling hardware is being designed to allow autonomous, semiautonomous, and manual operations.

The National Ignition Facility (NIF) will use about 8,000 large optics to carry a high-power laser through a stadium- size building, and will do so on a very tight schedule and budget. The collocated Optics Assembly Building (OAB) will assemble and align, in a clean-room environment, the NIF's large optics, which are the biggest optics ever assembled in such an environment. In addition, the OAB must allow for just-in-time processing and clean transfer to the areas where the optics will be used. By using a mixture of off- the-shelf and newly designed equipment and by working with industry, we have developed innovative handling systems to perform the clean assembly and precise alignment required for the full variety of optics, as well as for postassembly inspection. We have also developed a set of loading mechanisms that safely get the clean optics to their places in the main NIF building.

The predicted focal spot size of the National Ignition Facility laser is parameterized against the finish quality of the optics in the system. Results are reported from simulations which include static optics aberrations, as well as pump-induced distortions, beam self-focusing, and the effect of an adaptive optic. The simulations do not include contributions from optics mounting errors, residual thermal noise in laser slabs from previous shots, air turbulence, a kinoform phase plate, or smoothing by spectral dispersion. Consequently, these results represent `first shot of the day', without-SSD, predictions.

Large aperture multilayer hafnia silica high reflector coatings at 1064 nm, deposited by reactive electron-beam deposition, were prepared to examine different laser conditioning methods for manufacturing high fluence optics in the National Ignition Facility. Laser conditioning is a process where the damage threshold of the coating is increased or the damage that is created is minimized so that it does not grow upon further irradiation. Two laser conditioning methods were examined for coatings deposited from only oxide starting materials. Off-line laser conditioning consists of raster scanning a mirror past a 1 mm diameter Gaussian beam over the entire clear aperture; a process that takes approximately 24 hours per scan. On-line laser conditioning consisted of a large aperture 300 mm X 300 mm beam from the Beamlet laser that irradiated the entire full clear aperture of a series of mirrors; a process that was limited by a 2 - 4 hour shot rate. In both cases a six-step process was used with the mirror first irradiated at a low fluence, then successively higher fluences increased in equal increments up to the peak laser operating fluence. Mirrors that were only partially laser conditioned damaged catastrophically while fully conditioned mirrors survived fluences exceeding the safe operating Beamlet fluence. An alternative off-line laser conditioning method was examined for coatings deposited from hafnia or metallic hafnium sources. Single-step laser conditioning consists of off-line raster scanning an optic at the peak operating fluence, thus decreasing the laser conditioning cost by reducing the number of scans and required laser conditioning stations to process all the mirrors for the National Ignition Facility. Between pulses the optic is stepped approximately one fourth of the 1/e² Gaussian beam diameter so each area of the coating is irradiated by different segments of the beam starting at a low fluence at the outer edge of the beam diameter and increasing to the peak fluence in the center of the beam. The one-step conditioning results appear positive, but the influence of the coating improvements due to the metallic hafnium process on laser conditioning is undefined.

Although the plasma properties of CO₂ gas lasers have been extensively investigated there seems to be remaining uncertainties concerning the achievement of an optimized plasma state giving the best possible laser efficiency. Such optimization would be especially for high power lasers where a loss of some percents in efficiency can mean a considerable decrease for the laser output. To investigate the effects of plasma vs. rf interactions in longitudinal fast-flow CO₂ lasers a sufficient adequate plasma theory is used, based on the cross-sections of all involved processes. The main interest lies in the determination of all relevant parameters such as the electric field and current density along the electrodes which have pronounced dependencies on gas temperature and pressure. Although these variables change enormously in downstream direction the model reveals plasma coefficients which stay as unchangeable constants. Moreover, as is common for longitudinal fast-flow CO₂ lasers the electrodes are slightly inclined to obtain an increased laser performance, independent of the rf matching. By a rather simple consideration of plasma and rf interactions this effect can be basically explained so that an optimization for the best attainable efficiency is possible. The calculations are compared to measurements of different authors and are applied to a 6 kW fast flow coaxial system.

We report the development of a high-power Er:strengthened- glass laser emitting at the eye-safe 1.535 μm wavelength. The flashlamp pumped Cr:Yb:Er:glass produced 330 mJ output @ 0.45% slope efficiency. Thermo-optical measurements indicated strong thermal lensing, of 16 diopter/kW and mild birefringence induced depolarization of 5% at 200 W. In terms of radial and birefringence elastooptical coefficients these data determine the values of 0.075 ± 0.002 and 0.0094, respectively. For a hemispherical resonator configuration a TEM₀₀ beam was achieved.

We develop a method to precisely propagate short optical pulses through dispersive media with a cubic self-focusing nonlinear polarization. We show that above the critical cw self-focusing power, onset of pulse splitting into pulselets separated in time occurs, and for a certain regime of parameters a cyclic series of pulse splitting (into pulselets separated in time) and pulse recombination occurs for diffraction length smaller than dispersion length. At higher power, another threshold for non-cyclic temporal and spatial pulse splitting is manifest. The physics of these phenomena are described and delineated. We then incorporate self-steepening and self-frequency shifting. These effects can significantly affect pulse propagation dynamics, both in the normal but especially in the anomalous dispersion regimes. The nature of the dynamics is significantly different in the two regimes.

The paper presents the description of a high-power waveguide single-mode CO₂ laser generating 800 W average beam power and up to 1 kW peak power at pulse duration from 2 to 100 ms. The diffusion-cooled active medium is excited by a capacitive AC discharge of sound frequency. The advantages of the laser are: high (>10%) technical efficiency, upgraded stability of beam parameters at the cost of the use of waveguide generation mode, extremely low (<1 nl/h) consumption of lasing mixture and possibility of operation in quasi-sealed-off regime; design simplicity, compactness and low cost. As an example of application of various capabilities of these lasers, a description of the developed medical system `Genom-4' used in the transmyocardial revascularization (TMR) procedure is presented. The system is equipped with devices which are necessary both to conducting biophysical experiments and to performing operations under clinical conditions; among them are computer control system, cardiograph for synchronization of laser pulse with ECG of the heart under operation, remote articulated mirror manipulator with optical hand-piece for performing operations. The results of biophysical experiments on drilling channels in organic materials and biological tissues in vitro, as well as the results of operations on patients, are presented. Verification of a possible negative influence of shock waves, which can be generated in biotissues during the TMR procedure, has been studied. It has been shown that the pressure excess due to laser action is lower than one bar. Thus, no destruction of biotissues surrounding the channel should be caused. The autodyne Doppler spectroscopy diagnostics of specifying the moment of keyhole punching in myocardium has been discussed. Other possible applications of the system for drilling deep channels in liver, lungs, etc. are mentioned.

We propose the random polarization control plate (RPCP) to improve the illumination uniformity in ICF. The theoretical simulations show that the statistical characteristics of the intensity distribution created by use of the RPCP is greatly similar to that by use of combination technique of the polarization control plate (PCP) and random phase plate (RPP). This RPCP system employs only one element (RPCP), however, the combination of PCP and RPP uses two elements (PCP and RPP). Therefore this novel technique in this paper has some advantages compared with the combination technique, such as higher utilization ratio of laser energy, lower cost, easier fabrication and adjustment etc. and may become one alternative of the combination approach.

The experimental study of Nd:YLF-Nd:glass laser system with SBS pulse compression has been carried out. The necessary conditions for producing the shortest Stokes pulse by the SBS-in this system were determined. Nd:glass slab has been used as a final amplifier in this laser system. Two-pulse final compression system has been implemented for compression of high-energy pulses.

In laser welding of metals with a high power continuous CO₂ laser, a so-called keyhole is formed in the material. The keyhole greatly affects the absorption of laser and makes remarkable influence on the weld formation. Based on the energy balance in the keyhole, this paper presents an analytical mathematical model about the quantitative relationship between the weld formation and the welding parameters. The model takes into account of the plasma absorption for laser beam, and involves most of the important welding parameters such as laser power, welding speed, focal position, therm-physical properties of metal and the space shape of focused laser beam. The influence of the space shape of focused laser beam upon the weld formation is specially discussed. The beam space shape is dependent on the laser beam quality, beam formation system and focus position. The analysis shows that, when the focused beam become thinner and the focus depth become larger, the laser weld will be deeper and narrower. The influences of the beam quality, focal length and focus position on the weld formation are analyzed. Through comparison with the experiments carried on various laser processing systems with different focused beam shapes, the theoretical analysis is in good agreement with the experiments.

The optimization of LD end-pumped solid state lasers using a Monolithic Chip Assembly relies mostly on two factors: (i) the intensity and the geometry of the optical pumping, (ii) the critical phase matching temperature of the non-linear crystal which usually requires a temperature regulation.