The qualification of the thin disc laser concept for obtaining output powers in the multi-hundred watt class with good beam quality and high efficiency simultaneously is presented.The output power is scalable by increasing the pumped area at constant pump power density. Output powers of up to 255 W in multimode operation, diffraction limited beam quality as well as single frequency operation with output powers up to 28 W are presented.

Physical, spectral and laser properties of anew Yb³⁺ doped phosphate laser glass, QX/Yb, has been developed. This glass exhibits a low thermal expansion coefficient and a negative temperature coefficient of refractive index, resulting in an acceptable athermal behavior and an excellent thermal loading capability. The peak absorption and emission cross sections of Yb³⁺ were measured to be 1.06 X 10^-20 cm² and 0.903 X 10^-20 cm², respectively. The concentration quenching and the influence of the OH^- content on fluorescence lifetimes were examined. Excellent laser performance with a slope efficient of 49 percent and a maximum output power of 400 mW was demonstrated.

The various aspects of erbium glass laser characteristics were carefully examined, including the influences of pumping pulsewidth, dopant concentration, output wavelength, relaxation oscillation and energy transfer processing between Yb³⁺ and Er³⁺.

We have demonstrated the highest long-pulse efficiency and highest Q-switched energy reported to date for a Yb:S-FAP laser. THe Yb:S-FAP laser was pumped with a flashlamp pumped, free-running Cr:LiSAF laser. Threshold pump energy was extremely low, typically 30 mJ. Maximum output energy was 370 mJ at 1.047 micrometers with 650 mJ of pump incident on the Yb:S-FAP crystal. We obtained total optical-to-optical conversion efficiency of up to 57 percent in the long pulse mode. This is the highest conversion efficiency ever reported for this material in high energy, pulsed mode. Three samples of Yb:S-FAP of differing dimensions, doping, and crystal quality were tested. Two of the Yb:S-FAP crystals showing crystal defects experienced bulk damage during Q-switched mode of operation. The remaining crystal had the lowest dopant concentration of all the crystals, limiting the stored energy. Up to 65 mJ of output was obtained in this high-quality crystal, the highest ever reported in Q-switched mode with this laser material. Conversion efficiency at this energy level was 11.8 percent. However, the maximum efficiency obtained was 16.3 percent before pump bleaching effects started to occur due to low dopant concentration in this crystal sample.

The absorption characteristics of circular, offset, and rectangular double-clad fibers are investigated with simple and comprehensible 2D models. In the model, the pump modes in the first-cladding are divided into absorbable and unabsorbable modes. For circular fiber, a concept of absorbable power ratio is defined to characterize the effective absorption. For offset and rectangular fibers, almost all pump modes are absorbable, it is possible to achieve very high absorption efficiency. Such 2D models have been verified by 3D ray tracing simulations. The influences of offset distance for offset fibers, as well as cross sectional shapes for rectangular one on absorption are also discussed. The propagation losses of pump light in rectangular double-clad fibers are characterized both experimentally and theoretically. The measures to reduce pump loss in use of rectangular double-clad fibers are proposed. At last, the two ends of an Nd-doped rectangular double-clad fiber are bundled together to achieve efficient matching with a 10 W fiber coupled LD. With such a configuration, about 5.4 W pump light is launched into the first-cladding and 2.8 W laser output is obtained. A slope efficiency of 58 percent with respect to launched pump power has been achieved.

Liquid phase epitaxy (LPE) was used to grow LiY_1-x-yLn_xGd_yF₄ waveguides on LiYF₄ (YLF) substrates. Gadolinium co-doping increased the difference in the refractive index of the layer and the substrate materials. Buried waveguides were obtained by growing an YLF cladding layer on top of either planar or linear waveguides. Mechanical processing allowed to fabricate a ridge-type waveguide. Laser operation was achieved for a buried LiY_0.89Nd_0.01Gd_0.1F₄ ridge waveguide end-pumped with a laser diode operating at 806.5 nm. In the case of buried LiY_0.89Er_0.01Gd_0.1F₄ layers strong upconversion luminescence was observed in low optical loss waveguides.

Using stimulated Brillouin scattering (SBS) in glass fibers as phase-conjugating process, the field of applications of SBS phase-conjugators can be expanded, because fibers offer a low power threshold and a stable behavior even at high peak and average input powers. We have developed a new kind of phase-conjugator consisting of multimode quartz fibers with core diameters between 50 and 400 micrometers . In contrast to commonly used toxic liquids or gases under high pressure as SBS-materials, fibers are harmless to the environment and can be handled easily. Such fiber SBS-mirrors were characterized with respect to the phase conjugating parameters like threshold, reflectivity and fidelity. We achieved reflectivities of more than 50 percent, 93 percent fidelity, and less than 2 kW power threshold at 1 micrometers wavelength. A depolarization of the light could be reduced to less than 0.5 percent by proper configuration of the fiber. High power densities of more than 50 MW/cm² do not damage the phase conjugator. These new phase conjugators were applied in high-power Nd:YALO-MOPA-systems for the first time. Good beam quality at an average output power of more than 100 W was achieved at 1.08 micrometers wavelength.

The correction of wavefront distortion of laser beams propagating through laser media and optics is a key issue for developing high quality and high average power solid state lasers especially for ultra short high peak power lasers. For this purpose, we have been developing a closed loop wavefront control system composed of a Shack-Hartmann type wavefront sensor, personal computer, diagnostic computer and deformable mirror. We used two kinds of deformable mirrors, one of which is a stacked array type mirror (SAM) with 52 actuators, and the other of which is a Bimorph type mirror (BIM) with 13 electrodes. In the system, the phase-conjugate wavefront surface measured by the Shack- Hartmann type wavefront sensor is directly reconstructed on the deformable mirror. The response bandwidths of the control loop are 8.7 Hz for SAM and 13.5 Hz for BIM. In both cases, the root mean square (RMS) of wavefront distortion is reduced to less than 1/5 of original aberration of He-Ne laser. By applying SAM to solid state laser, the RMS of the wavefront distortion is reduced to 0.041 micrometers from 0.12 micrometers .

Recently, a new class of laser resonators was introduced by one of the authors that utilizes diffractive mirrors and an additional intracavity diffractive phase element. High modal discrimination and low fundamental mode loss were achieved simultaneously using sinusoidal and pseudo-random diffractive phase elements.In this paper, an analytical approach is developed to study a simplified diffractive mirror resonator for producing Gaussian-shaped beams. Explicit expressions are obtained for the fundamental mode loss and modal discrimination by assuming a Gaussian-shaped reflectivity for the output mirror. An intracavity phase element consisting of a simple single-step phase modulation was approximated by a Gaussian with small radius. Explicit expressions are obtained for the modal discrimination factor as a function of resonator parameters with a Gaussian output are obtained for the modal discrimination factor as a function of resonator parameters with a Gaussian output mirror. Analytical results demonstrate that simple single- step phase elements can enhance cavity performance. Numerical simulations were performed for a phase element with a step singularity in the phase function. This element was found to increase the modal discrimination of the cavity, while simplifying element fabrication and cavity alignment.

Industrial applications require lasers with high beam quality combined with kHz repetition rates. The average output power peak power and the repetition rate should be variable. Using phase conjugation based on stimulated Brillouin scattering (SBS) the beam quality of such high power solid state lasers can be improved significantly. High average power MOPA systems in double-pass configurations with SBS-mirror and high repetition rates were developed. To simplify multi-amplifier systems, Nd:YALO as active material was used to avoid depolarization of the amplified beams. With two amplifiers, average output powers of more than 200 Watts with high beam quality were realized. The system works with an average repetition rate up to 3 kHz and pulse widths of up to 200 ns. Peak and average output power can be varied over a wide range. Second harmonic generation with such a system leads to an average output power of 50 W at 540 nm wavelength with a conversion efficiency of 50 percent. Using SBS in glass fibers the power threshold for phase conjugation can be reduced and therefore first experiments with a continuously pumped Q-switched MOPA-system with SBS- mirror were realized.

Recent progress in pump sources and basic materials have allowed the production of commercially viable, high-power, diode-pumped, continuous-wave, green lasers. We will review the history and the technological developments that have allowed this progress.

The operational conditions of the OMEGA pulse-shaping require an extremely reliable and low-maintenance master oscillator. We have developed a diode-pumped, single- frequency, pulsed Nd:YLF laser for this application. The laser generates Q-switched pulses of approximately 160-ns duration and approximately 10 (mu) J energy content at the 1053-nm wavelength with low amplitude fluctuations and low temporal jitter. Amplitude and frequency feedback stabilization systems have been used for high long-term amplitude and frequency stability.

A difference was observed in gain coefficient between 'p' and 's' polarized light in a zigzag Nd:YAG slab pumped by a polarized laser diode array, indicating site selective excitation. The type of dipole involved in emission at 1064 nm seems to be predominantly (sigma) , although the ideal site symmetry is too low and no dipole axis is forbidden. These observations are consistent with others that show polarized site selection effects in Nd:YAG.

Intracavity-frequency-doubled diode-side-pumped Nd:YAG laser was developed. Maximum green power of 20 W was generated at 20-kHz repetition rate with 14.2 percent optical-to-optical conversion efficiency and 5.3 percent electrical-to-optical conversion efficiency.

We describe a computationally efficient numerical simulation model of optical parametric oscillators (OPOs) appropriate for the simulation of high energy pulsed OPOs using unstable resonators. The model calculations are time dependent and include the effects of diffraction and pump depletion in the parametric amplification process. The computational time required to solve the model equations for unstable resonator OPOs is reduced by applying a coordinate transformation to the paraxial three-wave mixing equations. An essential characteristics of this transformation is that it allows for the extraction of the geometric curvature from the intracavity fields resulting in the propagation of approximately collimated fields. We demonstrate the utility of this new model by presenting the results of a detailed numerical study of a high energy, non-critically phase matched KTA OPO using unstable resonators. Our results predict that an optimally designed confocal unstable resonator can produce near diffraction limited output at high pulse energies.

Laser-related properties of pyrromethene-580 doped modified polymethyl methacrylate, including conversion efficiency, operational lifetime, laser induced damage resistance of the polymer matrix and photodestruction of the impregnated dye, were studied under short-pulse and long-pulse laser pumping. High efficiency and operational lifetime have been achieved in the short-pulse mode. Effect of a laser resonator feedback on both the conversion efficiency and lifetime was revealed and studied in the long-pulse operation mode.

Dye-doped polymeric materials have ben developed for both laser-pumping and also flashlamp excitation. Spectroscopic properties of these hosts and other materials are reported. Successful laser operation has been achieved from ormosil and poly methyl methacrylate hosts doped with pyrromethene laser dyes. Conversion efficiencies in excess of 60 percent have been achieved from a less than ideal laser pumping geometry; output energies up to 132 mJ have been achieved from flashlamp-pumping of dye-doped rods.

The use of solid-state dye laser for commercial applications has been limited largely by the poor photostability of the gain medium. Techniques are examined to improve the photostability of Coumarin and Pyrromethene-BF₂ 567 (PM- 567) laser dyes within xerogel and Polyceram hosts synthesized by sol-gel processing. The photochemical mechanisms by which laser dyes degrade are discussed and determined specifically for PM-567. PM-567 was determined to degrade both by photo-oxidation and acid degradation. Techniques for improving photostability are described from a molecular engineering perspective. These techniques include: covalently attaching the laser dye to the host; controlling the chemical environment of the dye; increasing dye caging by increasing the SiO₂ content; removing porosity from the host; and incorporating additives such as hindered amine light stabilizers to minimize photodegradation.

Considerations for long-pulse operation of solid state dye lasers are discussed. The goal is to develop an all solid state dye laser which can be pumped directly with laser diodes. Experimental attempts to achieve long pulse operation will be described for rhodamine 700 dye in two different solid state hosts. Criteria for solid state dye host materials will also be presented.

A powerful photo- and thermostable, LiF:F₂⁺ color center laser pumped by radiation at 740 nm or at 683 nm is described. This is the first time an average power as high as approximately 1.4 W and an energy per pulse as high as approximately 100 mJ, with record real efficiency of 53 percent and 28 percent were achieved for a room temperature LiF:F₂⁺ color center laser. Such color center laser, tunable in the 820-1210 nm range, features a number of important advantages over pulsed lasers based on Ti or Cr doped crystals.

Using a xenon flash lamp as pump source, KTP as intracavity- doubling crystal and BDN dye film as passive Q-switch, the green laser output at 0.5295 micrometers from a new crystal Nd:Sr₅(PO₄)₃F has been demonstrated. The green laser output energy and pulse width were measured under the conditions of different resonator length and small-signal transmission of dye film. Meanwhile, the Q-switched coupling wave rate equations for intracavity frequency doubling were given an the experimental results agreed with the numerical solutions of equations.

The performance of Nd:S-VAP mode-locked laser by using iodoethane solution of BDN dye is reported. Pulse train energy is 1.5mJ; pulse width: 200ps; divergence: 0.6mrad.

Ultrabroadband nanosecond red-IR oscillation from longitudinally pumped Ti³⁺-sapphire laser has been achieved. The 'spatially-dispersive' laser resonator employed a prism pair, an intracavity cylindrical lens, and a diaphragm allowed to maintain the lasing conditions simultaneously for different spectral components in different areas of active element.

Nd:Sr₅(PO₄)₃F, known as Nd:S-FAP, is a new material for low-threshold high-efficiency miniature solid- state lasers. By using a tunable due-laser and a xenon flash lamp as well as a laser-diode pump as pump source, respectively, the performance of low-threshold high- efficiency Nd:S-FAP at 1.328 micrometers has been realized. The threshold energy and slope efficiency for different transmission of output reflector were measured. The characteristics of output laser, such as the emission spectrum, the output power, the output energy, the pulse width and so on, were presented.

This paper presents the design and realization of the cavity mirrors for a 2.94 micrometers Er laser, longitudinally pumped by a diode laser emitting in 0.97 micrometers range, used in stomatology applications. The total reflection mirror is a dichroic one with the third harmonic in reflectance spectral characteristic suppressed. The study on the harmonics suppression that we present was based on the theory of the finite thickness inhomogeneous layers and the results were used in the mirrors design. The theoretical and experimental reflectance spectral dependencies are presented.

Different ways to produce high-power short laser pulses have been investigated using low-Q short cavity dye lasers and a nanosecond laser pumping. A powerful 500-fs widely tunable ultrashort pulsed laser device is developed using a single standard nanosecond Nd:YAG laser as a pumping source. Two pulse-shortening techniques are combined within this compact and cheap dye laser device. The first technique, called the spectro-temporal selection, is extended to generation of < 100 ps pulses at wavelengths adjustable in the 320-700 nm spectral range. The second technique makes use of an extra- cavity pulse treatment of low-Q dye laser microcavity output pulses by nonlinear resonant processes in dye media to generate single 500-fs pulses. High-power continuously tunable subpicosecond pulses in the 430-850 nm spectral range are produced by supercontinuum generation, spectral selection and amplification in dye amplifiers. Using the pumping pulses from the nanosecond Nd:YAG laser, such a system has achieved 5-GW peal power levels between 50 nm and 670 nm.

High spectral purity, high energy, tunable laser sources operating in the absorption bands at 730, 815 or 940 nm bands are required for remote sensing of water vapor mixing ratio with a differential absorption lidar. For this application, injection seeding of a high energy Cr³⁺:LiSeAlF₆ ring laser with a narrowband, Q- switched, Cr:LiSAF laser was investigated. The slave ring laser utilized either a flashlamp pumped or diode-pumped Cr:LiSAF gain module. The flashlamp pumped module provided a single-pass gain of 1.5 at 825nm. The diode-pumped module consisted of a Cr:LiSAF rod, side-pumped with high power diode bar stacks giving > 150mJ energy in 200 microsecond(s) pulse. The spectral bandwidth of the ring laser output was 8 to 10 nm without injection seeding. The seed Cr:LiSAF laser was end pumped by a fiber coupled diode laser, and tuned with a birefringent filter. Tuning from 810 to 980 nm was possible with two sets of mirrors, and 160 to 700 ns long Q- switched pulses, with up to 40(mu) J energy, at 1000 Hz, were obtained with linewidths of < 0.1 nm. Successful seeding of both diode and flashlamp pumped lasers, narrowing of ring laser linewidth to < 0.1 nm, and 16 mJ/pulse output have been achieved.

The experimental study of 8 ns pulse compression in a three- stage scheme has been carried out. The initial pulses of a Nd:YAG master oscillator were first compressed by two stages of stimulated Brillouin scattering (SBS) in CCl₄, and then by a stage of stimulated Raman scattering (SRS) in compressed CH₄. That enabled us to obtain output picosecond pulses with a wavelength of 1.54 micrometers . The necessary conditions for producing of the shortest Stokes pulse by the SBS-stage were determined. SRS-stage characteristics were studied in detail.

The concept of biolaser is put forward and its operating mechanism is discussed for the first time in this paper Shawlow ever expanded quantum amplification technique in wavelength, and the author tries to make further exploration in laser active mediums which has only composed of non- living matter - to develop organisms as active mediums of stimulated emission. One of the examples of biolaser is Chinese Qi-gong. Using biolaser theory to expound the Qi- gong training method and its biological effects will significantly promote the development of Qi-gong theory and practice.

Nd:Sr₅(VO₄)₃F is anew material for efficient and miniature diode-pumped solid-state lasers. By using a laser- diode pump operating at 809 nm, a KTP as intracavity- doubling crystal, the intracavity frequency doubling Nd:Sr₅(VO₄)₃F laser at 0.5325 micrometers has been realized. The TEM_oo mode green laser output power is 25.6 mW at 200 mW incident pump power of the diode-laser. An optical efficiency of 12.8 percent and a laser threshold of 13.2 mW have been measured. Meanwhile, the way of improving efficiency is discussed.

The optical characteristics of organically modified silicates (ORMOSILs) are discussed. The absorption spectra of ORMOSIL samples undoped and doped with pyrromethene 580 were measured and compared. The doped sample was utilized in an oscillator/amplifier experiment. Output energies on the order to two millijoules were observed and an amplifier gain of 1.44 was measured.