High phase conjugate reflectivities (R > 10,000%) have been achieved through degenerate four-wave mixing in a cw diode-side-pumped Nd:YVO₄ amplifier and the interactions have been successfully modelled. This four-wave mixing geometry has subsequently been used in the design of a phase-conjugate resonator operating with a single- longitudinal mode TEM_oo near-diffraction limited output of > 7 W, which is capable of correcting for severe intra-cavity phase distortions.

An efficient, pulsed, solid-state, mid-wave infrared laser source has been designed and demonstrated that emits close to 4 micrometers . The pump laser was a diode-pumped neodymium- doped yttrium aluminum garnet slab. Periodically-poled lithium niobate provided the non-linear conversion in an optical parametric oscillator in a direct conversion from the pump source. An acousto-optical Q-switch was used for generating short-duration, high-intensity pulses. Modulated waveforms are possible via direct modulation of the diode sources.

We present here a compact 120 W, continuous-wave (CW), diode-pumped Nd:YALO laser at 1079 nm. This linearly polarized output from the optically anisotropic Nd:YALO crystal is advantageous for pumping non-linear crystals. The 1 at% doped Nd:YALO laser rod, 4 mm diameter by 97 mm long, is cut along the b-axis, with both ends anti-reflection coated at 1079 nm and 1341 nm. It is water-cooled (16 degree(s)C) and side-pumped by 5 close-coupled CW diode arrays operating at 803 nm. We obtained 121 W output at the maximum diode pump power of 571 W. The optical slope efficiency is 60%. This is, to the best of our knowledge, the highest power obtained from a diode-pumped Nd:YALO laser. We have studied this thermal lensing at different diode pump powers in lasing and non-lasing configurations. The measured thermal lens decreased from 37.5 to 11 cm as the pump power increased from 185 to 542 W in the lasing configuration. In the non-lasing case, the corresponding thermal lens decreased from 35.5 to 9.5 cm. We have also successfully operated our Nd:YALO laser at 1341 nm. We obtained a maximum output of 60 W, to the best of our knowledge, the highest diode-pumped laser output at this wavelength.

A high damage threshold, strain compensated, double quantum well InGaAs saturable Bragg reflector has been developed and successfully used to modelock a high average power, all- solid-state Nd:YVO₄ laser. A methodology for obtaining single transverse mode oscillation at high output powers was coupled with a `lens relay' approach to access practical cavity configurations. Ultrashort pulses of 21 ps duration were recorded at a repetition rate of 90 MHz and a diffraction limited average output power of greater than 20 W. By extending the laser resonator to give a pulse repetition rate of 36 MHz, a pulse duration of 25 ps was recorded and the Q-switching instability could be eliminated for all output power levels. In this configuration the peak power and pulse energy were in excess of 24 kW and 0.6 (mu) J respectively.

Passive Q-Switch characteristics of Co²⁺:MgAl₂O₃ sample were evaluated in a diode pumped QX/Er Erbium glass laser at 1535 nm, a flashlamp pumped Nd:YAG laser at 1.44 micrometers and Nd³⁺:KGd(WO₄)₂ laser at 1.34 micrometers .

A rod of solid state gain material centered between two flat end mirrors (i.e. the flat-flat resonator) is a common laser resonator configuration. Positive dioptric power in the rod, thermally induced by the pumping of the gain medium, enables the resonator to operate in the stable regime. A typical problem that may ultimately limit maximum power in lasers of this type is the susceptibility of the cavity end mirrors to laser-induced damage. A technique that mitigates this damage by increasing the intra-cavity spot width at the end mirror location is described. The resulting modified resonator is equivalent to the flat-flat resonator with regard to its output laser beam propagation parameters and to the symmetrical mode fill of the gain medium.

In this paper, a symmetrical optical resonator that contains the dual-telescopic elements and two rods used for a hybrid diode end-pumped and side-pumped geometry is investigated theoretically to generate high scaling laser output. The dual telescopes within resonators are appropriately chosen and adjusted to achieve a large-volume TEM_oo mode and to minimize the effects of the variations of the focal length in the rod. The movement of the optimal operation point of resonator caused by larger change range of pump power will be compensated by adjusting telescope defocusing. The resonator can also be applied for diode-pumped high-average- power solid-state lasers.

The performance (in terms of output power and slope efficiency) of the passively Q-switched Nd:YAG and Nd:YVO₄ lasers, both side pumped and end-pumped, will be reported and compared to our theoretical model. Passive Q- switch operation by a Cr⁴⁺:GGG element as a saturable absorber was studied in terms of pulse frequency as a function of pump power.

We have developed a highly efficient Nd:YLF oscillator- amplifier operating at 10 Hz. The design of both the oscillator and amplifier is based on conduction-cooled QCW diode bar stacks and a total internal reflection pumping geometry. The oscillator is designed as a gain guided confocal unstable resonator. Maximum electrical to optical efficiencies of 8.3% and 8.8% are demonstrated in the oscillator and amplifier, respectively.

The slim series DELTATRAIN^TM--worldwide the first integrated cw diode-pumped all-solid-state DUV laser at 266 nm with a compact, slim design--has been developed. The slim design minimizes the DUV DPSSL footprint and thus greatly facilitates the replacement of commonly used gas ion lasers, including these with intra-cavity frequency doubling, in numerous industrial and scientific applications. Such a replacement will result in an operation cost reduction by several thousands US$DLR each year for one unit. Owing to its unique geometry-invariant frequency doubling cavity- based on the LAS patent-pending DeltaConcept architecture-- this DUV laser provides excellent beam-pointing stability of <2 (mu) rad/ degree(s)C and power stability of <2%. The newest design of the cavity block has adopted a cemented resonator with each component positioned precisely inside a compact monolithic metal block. The automatic and precise crystal shifter ensures long operation lifetime of > 5000 hours of whole 266 nm laser. The microprocessor controlled power supply provides an automatic control of the whole 266 nm laser, making this DUV laser a hands-off system which can meet tough requirements posed by numerous industrial and scientific applications. It will replace the commonplace ion laser as the future DUV laser of choice.

High power diode pumped solid state lasers are auspicious sources for various applications in material processing. The solid state laser we report on is a Nd:YAG slab laser, that is partially end pumped from two ends by the line focus of two diode laser stacks. The pumped volume has a rectangular cross section. The resonator is configured, so that it is stable in the plane of small dimension and off axis unstable in the plane of large dimension of the gain cross section. Unlike conventional slab laser design, in which the laser beam takes zick zack path inside the slab crystal, in the present design the beam goes straight through the crystal with perpendicular end faces.

Diffraction gratings are proposed as an alternative technique to couple a laser diode pump beam into the YAG crystal of a solid-state laser. These binary diffraction gratings are on the long axis of the crystal and are etched in high refractive index coating material. The paper reveals the set of grating parameters and tolerances for transforming vertically incident light into horizontally propagating light inside the crystal with theoretical efficiencies of more than 90%. Under optimal conditions the diffraction grating behaves like an excellent leaky waveguide structure. Theoretical comparisons are made between the efficiencies of gratings directly etched into the laser crystal and gratings etched in to a high index coating material. The resulting zig-zag pumped laser cavity is uniformly excited in order to minimize thermal loads and lensing effects. The maskless binary sub-micron pattern transfer is realized by combining interferometry and lithography.

A systematic investigation on a series of Nd:YVO₄ crystals with different dopant concentration is conducted to scale the diode-end-pumped laser performance to higher powers. The analysis reveals that lowering the dopant concentration linearly extends the fracture-limited pump power and the thermal shock parameter plays an important role in the estimation of the fracture-limited pump power. The thermal shock parameter in Nd:YVO₄ crystals has been determined from the laser experiments. Based on the analysis, we demonstrate a compact and efficient diode-end- pumped TEM_oo laser with output power of 25.2-W for 52-W of incident pump power by use of a single YVO4 crystal with a Nd concentration of 0.3 at.%. In Q-switched operation 21-W of average power at a pulse repetition rate of 100 kHz and approximately 1.1-m pulse energy at a pulse repetition rate of 10 Hz were produced.

The radiation at around 1.5 micrometers has been extensively investigated over the last few years for eye-safe applications. This paper describes the development and performance of a pulsed solid-state laser based on nonlinear frequency conversion of the Nd:KGd(WO₄)₂ fundamental radiation into the near-infrared region of the spectrum. Neodymium-doped potassium gadolinium tungstate Nd:KGd(WO₄)₂ (Nd:KGW) possesses a combination of spectral and lasing characteristics uniquely favorable for laser operation. The explanation for the high efficiency which can be achieved with this material follows from high effective stimulated-emission cross section of laser transition. Also, in contrast to Nd:YAG, Nd:KGW is an efficient Raman medium. In the present paper most attention has been concentrated on the self-conversion of the laser wavelength at 1.351 micrometers to the first Stokes line at 1.538 micrometers . In conclusion, we have demonstrated a compact low-threshold source for the near-IR in a configuration of an intra-cavity solid-state Raman laser based on a flashlamp-pumped Nd:KGW laser crystal. The small size and high efficiency of this laser makes it an attractive source for a large number of applications such as communications and optical atmospheric studies.

The development of solid state tunable lasers in the ultraviolet region would have a wide range of applications, including atmospheric remote sensing, atmospheric spectroscopy and pollution monitoring. The first work with Ce:LiCAF was published in 1993, with subsequent reports on favorable results with Ce:LiSAF. While the original quality of Ce:LiSAF is superior, it suffers from solarization. In contrast, Ce:LiCAF shows minimal solarization and higher efficiencies, even with the typically high-scatter materials available. This presentation will summarize the crystal growth and material characterization of a series of colquiriite crystals with various Sr/Ca ratios. Based on these results, in addition to laser measurements, an optimum composition of Ce:LiSr_xCa_1-xAlF₆ will be determined.

This paper reports on the laser emission properties of Pyrromethene 580, Pyrromethene 597, Pyrromethene 650 and Rhodamine 11B in the novel matrix polymer-filled microporous glass (PFMPG). This host material combines the advantages of an organic environment for the dye with the superior thermooptical and mechanical properties of an inorganic glass. Laser efficiency was measured as a function of pump flux for different dye concentrations, resonator feedback, and locations on the sample. Service life, defined as the number of pulses for the output to drop to the 70% point, was recorded at 5 Hz for the higher dye concentrations. The highest efficiencies were observed for Pyrromethene 597 (is congruent to 70%), which had a service life of is congruent to 60,000 shots at 25 MW/cm² and is congruent to 45,000 shots at 50 MW/cm². The longest service life was measured for Rhodamine 11B (is congruent to 110,000 pulses at 25 MW/cm²), but this dye had somewhat lower efficiency (is congruent to 50 - 55%). Thermal lensing measurements were made for dye-doped PFMPG and MPMMA, and showed that the lensing is much lower in the hybrid matrix. The agreement with the theoretical modeling is very good.

The main photodegradation mechanisms of pyrromethene 567 are discussed, and the quantum efficiency of self-sensitized photo-oxidation, the predominant mechanism, was found to be 0.5% in aerated benzene-d₆. Other degradation mechanisms do exist, but the high photostability of the dye in solid host media possibly implies that they are all diffusion controlled. Solid-state dye lasers based on pyrromethene 567 doped poly(methyl methacrylate) with an added singlet oxygen quencher 1,4-diazobicyclo [2,2,2] octane showed a lifetime of 550,000 pulses. A triplet quencher, perylene, provided no improvement. Singlet oxygen quenching is effective in the solid-state whereas triplet quenching is not, presumably due to the slower diffusion rate of dye molecules compared with oxygen.

Studies of the lasing characteristics of three pyrromethene laser dyes (pyrromethene 567, 580 and 597) in modified polymethyl methacrylate have been carried out under flashlamp excitation. Comparison are made of the optical qualities, output energy and other lasing properties. Output energies of over 1 Joule per shot have been achieved with an electrical stored energy to output energy efficiency of almost 0.5%.

Injection of high power, multi-mode laser profiles into a fiber optic delivery system requires controlling a number of injection parameters to maximize throughput and minimize concerns for optical damage both at the entrance and exit faces of the fiber optic. A simple method for simultaneously achieving a compact fiber injection geometry and control of these injection parameters, independent of the input source characteristics, is provided by a refractive lenslet array and simple injection lens configuration. Design criteria together with analytical and experimental results for the refractive lenslet array and short focal length injection lens are presented. This arrangement provides a uniform spatial intensity distribution at the fiber injection plane to a large degree independent of the source mode structure, spatial profile, divergence, size, and/or alignment to the injection system. This technique has application to a number of laser systems where uniform illumination of a target or remote delivery of high peak power is desired.

Today's high power diode lasers achieve spots with dimensions of approximately 1 mm square, delivering intensities breaching 10⁵ W/cm² and power levels of up to 4 kW. These lasers can be used for a variety of applications from surface treatment to welding. However, each of these applications require different focus sizes to maximize the benefits of the laser source. Therefore, variable cylindrical optics were designed and manufactured in the scope of this work. They create rectangular spot sizes with adjustable aspect ratios. These optics are used in connection with high power diode laser stacks operating in the multiple kilowatt power range. Two different variable optics were used. The first is designed for surface applications such as hardening, cladding and alloying. The spot size varies from 6.0 mm to 22.0 mm in one direction and stays constant at 2.6 mm in the other direction. The second optic exhibits two ranges of continuously variable spot sizes from 1.2 mm to 6.0 mm and 2.4 mm to 12.0 mm with its second dimension fixed at 1.2 mm or 2.4 mm respectively. This lens is used for applications from surface treatment to welding and cutting.

Thermal effects dramatically influence the laser performance of diode-pumped solid state lasers (DPSSL). There are three factors accounting for thermal effects in diode-pumped laser medium: the change of the refractive index due to temperature gradient, the change of the refractive index due to thermal stress, and the change of the physical length due to thermal expansion (end effect), in which the first two effects can be called as thermal parts. A laser interferometer is proposed to measure both the bulk and physical messages of solid-state lasing medium. There are two advantages of the laser interferometry to determine the thermal lensing effect. One is that it allows separating the average thermal lens into thermal parts and end effect. Another is that the laser interferometry provides a non- invasive, full field, high-resolution means of diagnosing such effects by measuring the optical path difference induced by thermal loading in a lasing crystal reliable without disturbing the normal working conditions of the DPSS laser. Relevant measurement results are presented in this paper.

Thermal conductivity and expansion coefficient of YAG laser crystals vary greatly with temperature. In order to obtain an accurate solution, finite element analysis is employed to solve the heat equation. By comparing the finite element analysis with the conventional analytical analysis, we found the temperature difference between finite element analysis and conventional analytical analysis is small and the conventional analytical solution for temperature is still available; the stress difference between finite element analysis and conventional analytical analysis is large, so we need treat the thermal conductivity and the expansion coefficient as non-constants when calculating the stresses in laser rods.

A general concept of real-time detection of organic molecules via resonance enhanced multi-photon ionization (REMPI) was illustrated for the molecule indene at LASE '99. This paper focuses on benzene and toluene, which are ubiquitous components of fuels and widespread environmental contaminants in soil and groundwater. The 266.0 nm 4th harmonic wavelength from a Nd:YAG laser falls within the first UV absorption system of single ring benzenoid compounds, but overlap with the structured absorbance bands exhibited by benzene and toluene is poor. Tunable solid state laser options under consideration include Yb:YAG and Nd:KGW, although most of the work to date had been performed with a frequency-doubled tunable dye laser. A heuristic model of the REMPI process that considers laser wavelength and pulse energy, duration, and repetition frequency has been developed for evaluating laser options. Studies to determine the overlap of a free-running (i.e., non-tuned) Nd:KGW laser with benzene and toluene absorbance features are underway, as are determinations of the saturation fluences.

Recently, erbium-based lasers engineered to emit at the shorter 2.69 - 2.71 micrometers transitions have demonstrated desirable therapeutic results with tolerable thermal tissue damage in dental and ophthalmic applications. Moreover, transmission of the 2.69 um radiation through an ordinary low-OH silica fiber with acceptably low losses has been achieved. In addition to medical and dental applications, the 2.62 and 2.69-micrometers radiation from CrTmEr:YAG (CTE:YAG) is also suitable as a pump source for nonlinear materials in order to generate radiation in the 3 - 14 micrometers region. In the present work, stable and efficient room-temperature operation of a flashlamp-pumped CTE:YAG laser operating at the 2.69 micrometers transition is reported. The optimization of the dopant concentrations, the spectral characteristics of the resonator optics, and the AR coatings on the laser rod have resulted in a laser that emits radiation only at (lambda) equals 2.69 micrometers for incident pump energies as high as 250 J/pulse. In the free running mode, output energies approaching 1 J/pulse at a repetition rate of 4 - 6 Hz, and slope efficiencies of approximately 0.6% have been achieved. In the Q-switched regime, output energies of 35 - 50 mJ in the fundamental TEM_oo mode have also been achieved.

Q-switched operation is very common and important for diode- pumped solid-state lasers. In this paper, we reported a novel use of GaAs wafers as Q-switch elements as well as output couplers for DPSS lasers. A pulse duration of 2.6 ns at the wavelength of 1064 nm was obtained from a diode- pumped and passively Q-switched Nd:YVO₄ laser using a piece of GaAs wafer as the saturable absorber as well as the output coupler. The transmissivity and the absorption coefficient of different wafers were studied. The experimentally measured results indicated that the transmissivity of different GaAs wafers varied from as low as approximately 32% to as high as approximately 75%. It was found that some of those wafers showed Fabry-Perot effect and it could affect the effective transmissivity and produce lower transmission, and thus shorten the pulse duration and stabilize the laser operation.

Pulsed Nd-glass lasers usually have low beam quality (200 - 300 mm-mrad), and are used only for surface hardening of metals. However, high pulse energy make them feasible for deep penetration welding if their beam quality could be improved. We investigated beam properties of Nd-glass laser with unstable resonator with semitransparent output coupler (URSOC). We had found that beam divergence of the laser with URSOC was an order of magnitude smaller than that of the laser with stable resonator. The achieved beam quality (40 - 50 mm-mrad) permitted to perform deep penetration welding with the aspect ratio of approximately 8. For beam divergence of 3 mrad melt depth of 6.3 mm was achieved with the ratio of depth to pulse energy of 0.27 mm/J.

Development of a three-color solid-state laser on phosphate neodymium glass for pulse holography is offered in the present paper. The laser has been assembled under the multicascade scheme with a single master oscillator. The powerful infra-red radiation on an output of such system has been frequency converted into green, dark blue and red radiation due to processes of the second harmonic and third harmonic generation of a neodymium laser radiation and generation of first anti-Stokes component of the Simulated Raman scattering respectively and has been divided into three various beams of different color. Varying the conditions of realization of above processes, it is possible to redistribute the radiation energy of the system between beams of various colors over a wide range. The energy of each beam will be sufficient for exposition of a photomaterial of the appropriate spectral sensitivity, and the joint influence of beams will make possible to obtain color pulse holograms and, in particular, color holographic portraits.

In this paper, the stability of laser-diode-pumped passively Q-switched lasers with a Cr⁴⁺:YAG as the saturable absorber and an Nd³⁺:YAG or an Nd³⁺:SFAP as the gain medium is studied. First, the influence of the transversal mode structure on the stability is investigated. Then, with the laser operating in TEM_oo mode, the variations of the pulse energy fluctuation and the repetition rate fluctuation as functions of the repetition rate are measured. Finally, the repetition rate fluctuation and the pulse energy fluctuation are semi-quantitatively and qualitatively analyzed, respectively.

This paper presents the experimental results of a CW laser- diode end-pumped passively Q-switched Nd³⁺:YAG laser with a Cr⁴⁺:YAG saturable absorber and two groups of theoretical results. The first group is obtained by numerically solving the passively Q-switched laser rate equations in which the spatial variation of pumping and intracavity laser intensity is taken into account. The second group is obtained from the analytical solutions of Q- switched laser rate equations under the plane-wave approximation. The comparison shows that the first group is more close to the experimental results.

By using a laser-diode as pump source and saturable absorber Cr⁴⁺:YAG as passive Q-switch, a KTP as intracavity frequency doubling crystal, we have realized green Q- switched laser output at 0.5295 micrometers from a Nd:S-FAP crystal. The output green laser characteristics, such as the average power, the single pulse energy, the pulse width, the repetition rate for different small-signal transmission of Cr⁴⁺:YAG and different pump power, were measured. Meanwhile, the coupling rate equations of intracavity frequency doubling for Cr⁴⁺:YAG as passive Q-switch were given and the numerical solution of equations agreed with the experimental results.

The LiF:F₂^+** laser as been shown to provide high power (hundreds of mJ), efficient (tens of %), room temperature stable laser operation tunable from 800 nm to nearly 1210 nm. However, no reasonable explanations were provided for such an ultrabroadband tuning capability using this active medium. This work describes the mechanism of the ultrabroadband lasing from LiF:F₂^+** under Alexandrite laser pumping. Alexandrite laser pump radiation corresponds to the region of spectral overlapping in the absorption bands of two color center in LiF, namely F₂^+** and a new F₂^+**-like center, conclusively discovered in this work. Using the Alexandrite laser's excitation, we can achieve simultaneous population inversion in both centers making F₂^+** and the F₂F^+**-like centers, the primary color centers responsible for the ultrabroadband tunability. This work details the temperature-dependent spectroscopic measurements of these two color centers and the resulting laser characteristics. Absorption and fluorescence measurements were performed from 300 K to 13 K. The room temperature (RT) absorption data shows that the F₂^+** center has maximum absorption at (lambda) ⁰_abs equals 614.5 nm and FWHM, (Delta) v equals 3819 cm^-1; the F₂^+**- like center has RT absorption at (lambda) ^o_abs equals 813.4 nm and FWHM, (Delta) v equals 3592 cm^-1. The fluorescence of both centers was measured using several excitation wavelengths from 532 nm to 778 nm. F₂^+** demonstrated fluorescence emission from 765 - 1080 nm, corresponding to 10% of maximum, and F₂^+**-like from roughly 890 - 1400 nm, with fluorescence maxima at (lambda) _fl equals 905 nm and (lambda) _fl equals 1098 nm, respectively.

The spectral evolution of broadband dye laser emissions generated from low-Q, short laser resonators have been investigated experimentally and theoretically with a rate equation model extended to a multiwavelength analysis. The influences of cavity quality and pumping parameters on the spectral dynamics of the broadband dye laser emissions are studied. From these results, the development of a picosecond pulse compressor and direct generation of tunable picosecond (< 90 ps) dye laser pulses are demonstrated using a single nanosecond pumping laser and a spectro-temporal selection of dye broadband laser emission.

In this paper, the Ti:sapphire laser has been demonstrated with astigmatic compensated fold cavity of 3-mirror and 4- mirror standing wave cavities pumping by an internal frequency-doubled AO Q-switched Nd:YAG laser. The basic properties of 4-mirror cavity are analyzed theoretically by G-parameter. Up to 0.95 W output with 13.6% of efficiency in 4-mirror cavity and 0.77 W output with 11% of efficiency in 3-mirror cavity are obtained when pump power is 7 W, the tuning range from 720 nm to 820 nm with peak power wavelength at 800 nm is achieved. The experimental results are compared and discussed.

By using a mirror whose reflectivity is dependent on wavelength as the output coupler of a Cr⁴⁺:YAG tunable laser pumped by 1.06 micrometers Q-switched pulses, the dependence of the Cr(superscript 4+$:YAG laser pulse characteristics on wavelength is greatly weakened and the whole efficiency of the laser is greatly enhanced.

The calculations of the phase conjugation at the stimulated Brilloiun scattering (SBS) of the laser pulse specific for such powerful laser facilities as NIF, MEGAJOULE, ISKRA-6 are carried out. A computer code based on the most complete in literature physical and numerical model of non-steady- state SBS is applied for this purpose. Transient processes and an effect of Stokes field on laser one (the laser pump depletion) are included. The possibility is demonstrated of obtaining the phase conjugation of the profiled laser pulse with temporal phase CPA modulation needed for ICF experiments in order to replace an adaptive mirror in multi- pass laser scheme by an SBS mirror. The laser spectral line width is greatly larger than the SBS spectral line width. It is obtained that the phase conjugation of broad-band laser focused beam with the complicated temporal power profile is feasible. When a minimal laser coherence length scale (dealt with an inverse width of spectral line) is more than or of order of a beam waist length, the Stokes beam is characterized by the high phase conjugation quality that is about 97%. At the enhancement of the laser modulation frequency, when the coherence length is shorter than the beam waist length by 10 times, the phase conjugation fidelity reduces to 80% and the SBS threshold rises.

Kane and Byer reported the first monolithic non-planar miniature ring lasers in 1985. An intrinsic optical diode enforces unidirectional and hence single-frequency oscillation of this device. It has the advantages of compactness, reliability and high efficiency. We put forward another form of the non-planar ring lasers, in which the corner cube prism is the key element and the Nd:YAG crystal is used as a Porro prism to enclose the ring resonator. The phase shift due to the total internal reflections of the three differently orientated reflection planes of the corner cube prism, Faraday rotation in the Nd:YAG crystal placed in a magnetic field and the different output coupling in S and P polarization form an optical diode and enforce the single- frequency generating. A round trip analysis of the polarization properties of the resonator is made by the evaluation of Jones matrix. The results of our initial experiment are given in the paper.

A four-pass quadrature frequency conversion scheme was developed to generate green output with high efficiency for pumping an ultrashort pulse laser system. With this scheme, a efficiency from fundamental energy into total second harmonic energy in excess of 80% was achieved for frequency doubling of 1064-nm in KTP with a low input fundamental laser intensity of 76 MW/cm². A total second-harmonic output of 486 mJ was obtained with 607 mJ of the input 1064- nm fundamental laser at 10 Hz.

For medical applications tunable solid state laser system emitting a visible light in a region from 710 to 775 nm was developed. Laser head of this system was composed of alexandrite crystal rod (4 mm in diameter, 90 mm of length), two dielectric mirrors and tuning element (dispersing prism or thin-film polarizer). For Q-switching, three different optics shutters were proved: a saturable NC-dye or LiF crystal, LiNbO₃ Pockels cell, and rotating prism. Maximum output energy in free-running and Q-switching regime was 400 mJ and 70 mJ, respectively. The pulse duration was 70 microsecond(s) in the free-running and 45 - 250 ns in Q-switching regime. The output free running laser radiation was guided via a multimode quartz fiber (1 m of length, core diameter 600 micrometers ) or via a special fluorocarbon polymer-coated silver hollow glass waveguide (0.62 m of length, inner diameter 1 mm). At first, this radiation with a laser fluence of 2.5 J/cm² was used for an ablation of a dental calculus. Next, the laser radiation propagation in a root canal and its effect on bacteria was proved. The dissipated energy measurement was made inside and outside of the tooth. From the results follow that the alexandrite laser could be useful for medical applications.

This paper analyzes the lasing performance of Yb:YAG and Nd:YAG laser. The authors deduced the formulas used here on lasing threshold and slope-efficiency. The effective reflectivities of plane-plane laser cavity are 90% and 99% respectively. It is obtained that the crystal length is about 0.2 cm corresponding to the minim threshold for 6.5 at% Yb:YAG. With the increasing of the crystal length, the threshold for Nd:YAG laser goes to stable. It is also deduced that the slope efficiency of Yb:YAG is twice as much as that of Nd:YAG, and the output power of Yb:YAG laser is possibly higher than that of Nd:YAG when the input power is properly high.

A compact, 2-J Master Oscillator, Power Amplifier (MOPA) laser system was designed and built to support a multiple- fiber injection experiment. The system was built in a breadboard configuration to support a risk-reduction/proof- of-concept effort. A common design approach for MOPA systems is to utilize a single-mode oscillator as the input source to the amplifier. However, to optimize this system for fiber injection, a multi-mode oscillator was chosen. A stable, multi-mode, 1053-nm, Nd:YLF laser oscillator was designed and built. A plano/concave resonator was utilized, with a 4.0-mm diameter Nd:YLF laser rod, pumped in a dual flashlamp, diffuse, close-coupled pump cavity. A lithium niobate (LiNbO₃) Q-switch crystal was used in a quarter- wave scheme. This pump cavity design did not use any active cooling and was ideal for low duty cycle applications requiring no more than one shot every 60 seconds. The oscillator output was amplified using a neodymium-doped phosphate glass laser rod in a four-pass configuration. Two Joules of output energy with an output pulsewidth of 12 ns were obtained. The 9.53-mm diameter Nd:Glass amplifier rod was pumped in a dual flashlamp, diffuse, close-coupled pump cavity. Output energy, pulsewidth, far-field beam divergence and intensity profile results will be presented for a Schott LG750 amplifier rod.

The spectroscopic properties of Yb³⁺:Y₂SiO₅ (Yb:YOS) and its laser potential for 1 micrometers emission are investigated. Crystals containing 5% of Yb³⁺ ions (9.2 X 10²⁰ ions/cm³) with very good optical quality have been grown by the Czochralski process. An energy-level diagram for Yb³⁺ in this host is proposed, taking into account electron-phonon coupling phenomena. A broad emission, from 0.98 micrometers to 1.1 micrometers , with a lifetime of 1.5 ms have been measured and the laser parameters indicate that this host could be well adapted for high power lasers. In good agreement with the spectroscopic predictions, laser oscillation under Ti:sapphire laser pumping was observed for the first time, on uncoated crystals in a plano-concave cavity. A slope efficiency of 44% and a laser threshold around 160 mW have been obtained. This laser material appears very attractive for the development of new Yb³⁺ sources.

We have grown neodymium doped mixed apatite crystals, (Sr_xBa_{1- x})₅(PO₄)₃F, Sr₅(P_1-xV_xO₄)₃F, and Ba₅(P_1-xV_xO₄)₃F, and spectroscopically studied them as potential gain media for a laser source for atmospheric water sensing operating at 944.11 nm. We conclude that an appropriate apatite host material for a 944.11 nm laser should be a mixture of Sr₅(PO₄)₃F with a small fraction of Ba₅(PO₄)₃F. The precise wavelength tuning around 944.11 nm can be accomplished by varying the host composition, temperature, and threshold population inversion. In apatite crystals of mixed composition, the amplified spontaneous emission loss at 1.06 micrometers is predicted to be significantly smaller than that in the end members.

To date, typical high-power dye laser systems use flash lamps as the optical pump source. No more than 10% of the flash lamp's optical energy can be absorbed by the singlet ground state of current laser dyes. Most dyes have a conversion efficiency of 30%, so system efficiencies are typically a few percent. To overcome this problem, an efficient optical pump source that matches the ground state absorption of the dye is required. Light Emitting Diode (LED) technologies are rapidly maturing which emit in the yellow, green, and to a lesser extent into the blue of the optical spectrum. Intrinsic efficiencies of 60% for LEDs are now achievable, greatly surpassing flash lamp efficiencies. Some LEDs can emit > 1 Watt of peak power when pulsed by a > 10 nanosecond wide current source. With these increased LED efficiencies, the output of which can be matched to the absorption of laser dyes, it should be possible to achieve overall system efficiencies greater than 10%. A mathematical model is constructed in order to estimate the performance of this type of system and to guide the development of new high efficiency laser dyes and matched LED pump sources.