Developments in Cr lasers at AlliedSignal are reviewed. Performance of several lasers is described, including several commercial lasers and Cr:LiSAF experiments.

The ultraviolet laser properties of LiSrAlF₆ doped with trivalent cerium (Ce:LiSAF) and LiCaAlF₆ (Ce:LiCAF) are reported. The polarized absorption, emission and excited state absorption cross sections for both Ce:LiSAF and Ce:LiCAF were determined for the 266 nm pump and 290 nm laser emission wavelengths. The single exponential emission lifetime was measured to be 28 +/- 2 and 25 +/- 2 ns for Ce:LiSAF and Ce:LiCAF, respectively. The gain was found to be highest when the probe was polarized parallel to the optic axis of the crystal due to the anisotropic nature of the excited state absorption. The excited state absorption is ascribed to a transition from the 5d orbital of Ce³⁺ to the conduction band of the host. Laser slope efficiencies of up to 29% and 21% were measured for Ce:LiSAF and Ce:LiCAF when the 266 nm pulsed pump beam was polarized parallel to the optic or c- axis. These are the highest laser slope efficiencies yet observed for any known solid-state ultraviolet laser material. When the pump beam was polarized perpendicular to the optic axis of the crystals, the gain and laser efficiencies dropped by up to an order of magnitude. The magnitude of pump-induced solarization was found to be highly variable for different crystals, and to have insignificant impact on the laser performance when favorable crystals were utilized.

Production refinements and pragmatic optical properties of the frequency converter crystal KNbO₃ (KN) are highlighted regarding its commercialization. The growth, morphological orientation, and processing of KN crystals into devices are outlined. Passive absorption data are presented that define the effective window range for KN devices. An absorption band at 2.85 micrometers is attributed to the presence of OH groups in the crystal, and its vibrational strength varies with crystal growth conditions and incident polarized light orientation. Although blue light induced infrared absorption (BLIIRA) can reduce second harmonic generation (SHG) efficiency at high powers, single-pass conversion efficiencies of 1%/W(DOT)cm may be achieved with incident fundamental powers of 10 W. The ability of KN to noncritically phasematch by temperature tuning provides blue-green wavelengths; together with critical angle-tuned phasematching, the entire visible spectrum may be accessed with efficient SHG conversion.

New solid-state passive Q-switch materials for the Er:glass laser at 1.53 micrometers are described. Saturable absorber Q-switching has been obtained using U⁴⁺:SrF₂, Er³⁺:CaF₂, and Er³⁺:Ca₅(PO₄)₃F.

The characteristics of the green ((lambda) approximately 550 nm) holmium upconversion fiber laser have been studied in detail in Ho:ZBLAN fibers ranging in length from approximately 20 to 86 cm. When pumped in the red (approximately 643 nm), slope efficiencies up to 24% are observed for a 21 cm long fiber and a cavity output coupling of 30%. More than 38 mW of output power is observed for 280 mW of absorbed pump power. The influence of the depletion of the ground state (⁵I₈) population on the emission spectrum and overall efficiency of the oscillator are discussed.

The 1.645 (mu) laser action in Er³⁺:Y₃Al₅O₁₂ (Er:YAG) at 300 K was studied using the 1.532 micrometers Er:glass laser for excitation. Laser action was with Er concentrations ranging from 0.5% to 4%. Slope efficiencies as high as 40% were obtained with 0.5% Er:YAG. Laser threshold results indicated that for this Er concentration range upconversion losses were small (negligible for 0.5% Er).

The production of the laser host material YVO₄ via high temperature solution growth (HTSG) is described as a facile alternative for producing optical quality crystals for research. The effects of dopant concentration on optical absorption properties in 0.7% and 3% Nd:YVO₄ crystals are discussed. The rare earth ions Ho³⁺ and Er³⁺ have been doped into YVO₄ with the HTSG method, and inaugural optical properties of Ho_0.04Y_0.96VO₄ are presented.

Dielectric phase-anisotropic laser mirrors have been proposed for a two-frequency gas laser with orthogonal linear-polarized modes. Under normal light incidence the reflection phase (but not reflection amplitude) of the mirrors depends on light polarization. The mirrors consist of dielectric multilayer and anisotropic elements. One or several dielectric layers with surface- relief diffraction gratings of small period d < (lambda) have been proposed as the anisotropic element. Results of numerical and experimental investigations of the mirrors are presented. Two-frequency oscillation with up to 5 MHz frequency difference have been obtained in a gas laser with internal mirrors.

Solid state lasers have been utilized for many varied applications. This application describes how the high peak power, short pulse capability of an alexandrite laser, in combination with a generation III image intensified receiver, can solve the problem of very long range target identification. Applications have relevance to both commercial and military uses where day/night all weather imaging is required. Wavelength diversity provides single and multispectral system capability, therefore allowing discrimination of targets against varied backgrounds.

Solar blind ultraviolet communication techniques have promise to address the military's needs for short range applications where non-line-of-sight and a low probability of interception and detection is required. This paper addresses the general requirements for these systems and discusses an example system developed using a compact quadrupled Nd:YAG laser.

A compact line-narrowed 248 nm solid state laser source operating at 15 mJ 100 Hz PRF was demonstrated. Constraints due to thermal loading of components were addressed. Tradeoffs between pulse energy and repetition rate were investigated. A method for overcoming thermal dephasing in the THG material was achieved by scanning a slab shaped crystal.

An angularly multiplexed XeCl excimer laser system, generating pulses of 4 - 5 ns duration, has been used to investigate soft x ray generation from laser-produced plasmas. For applications in x-ray lithography, the spectral regions of 10 - 15 angstrom and around 135 angstrom have been studied. A laser to x ray conversion efficiency of 5.5% and an x ray power of > 1 W into 2 (pi) steradians have been demonstrated in the shorter wavelength band. At the longer wavelength, the effects of laser intensity and plasma recombination on conversion efficiency have been studied.

The ⁴I_13/2 - ⁴I_15/2 laser action in Er³⁺:Y₃Sc₂Ga₃O₁₂ (Er:YSGG) at room temperature is described. We obtained 1.643 micrometers laser action from a 1 cm long 0.7% Er (3% Yb, 1% Cr):YSGG crystal with a 20 mJ pump threshold and an 8% slope efficiency utilizing an Er:glass 1.532 (mu) pump laser.

The present work demonstrates a high-resolution technique for the optical detection of the phase and amplitude of high frequency surface acoustic waves (SAWs). The test setup incorporates a mode-locked picosecond laser, harmonic mixing, and coherent detection, and it allows not only the measurement of the surface wave field but also the direct determination of the phase velocity. A measurement bandwidth in excess of 2 GHz is achieved. The maximum scan length was 4 cm. As a substrate, LiNbO₃ has been used for the test measurements. Minimum detectable surface displacement and dynamic range were 1 pm/Hz^1/2 and 40 dB, respectively. The method enables the determination of the phase velocity with a resolution of 1.5 (DOT) 10^-5 in dependence of crystal cut, temperature, and frequency. An additional feature is that phase velocity values can be obtained with spatial resolution, i.e., velocity variation effects along the propagation path can be evaluated. We found that the assumption that the SAW velocity is constant across the whole device surface is not valid in general.

The frequency doubled Nd:YAG-pumped performance of two pyrromethene-BF₂ complex laser dyes in a modified acrylic polymer host is described in detail. Optimization experiments included changes in output coupler reflectivity and determination of the slope efficiency in a simple end-pumped oscillator cavity. A slope efficiency of 88.8% was achieved for the PM- 567 laser dye in the solid host.

The development of solid state dye lasers could lead to a major breakthrough in the cost and compactness of a medical device. Advantages include: elimination of the flow system for the gain medium; ease with which to implement wavelength agility or the replacement of a degraded rod or sheet; and toxicity and flammability become a non-issue. Dye lasers have played a role in cardiology, dermatology, and urology. Of these cardiology is of interest to Palomar. The Palomar Model 3010 flashlamp-pumped dye laser medical device was used during phase 1 FDA clinical trials to break-up blood clots that cause heart attacks, a process known as coronary laser thrombolysis. It is the objective of this research and development effort to produce solid matrix lasers that will replace liquid dye lasers in these medical specialties.

Experiments that are designed to investigate the viability of polyacrylamide gel as a prospective host for use as solid state dye laser rods are described. We present data for absorption and fluorescence spectra for dye-doped gel samples. We also describe preliminary Nd:YAG second harmonic pumping of dye-doped samples within a simple dye laser optical cavity. We observed efficient dye laser oscillation.

In the paper the up-to-date state of investigations and developments of active polymer materials, elements, and lasers on polymer matrices is stated. The original part of the work is based on results obtained when investigating elastic polymer matrices whose technological, photophysical, and thermo-optical properties thoroughly satisfy requirements to an active medium.

In many respects solid polymers are attractive hosts for dyes to produce on their base various optical elements for laser applications including tunable lasers and laser beam control saturable filters. For this reason various dye-impregnated polymer materials were extensively studied in many laboratories during last 25 years. A critical review of these studies is presented in this paper with main attention to analysis of processes responsible for major laser characteristics of dye - impregnated polymer materials: lasing efficiency, bleaching efficiency, laser damage resistance of polymer matrix, photostability of dyes under high power laser radiation and dye deterioration during long-term use and storage. Results achieved in General Physics Institute of Russian Academy of Sciences and collaborating industrial research laboratories on creation of highly effective dye-impregnated modified polymer materials for visible and near IR laser application possesing high laser damage resistance, dye photostability, laser oscillation efficiency and laser induced bleaching efficiency are presented. Limitations for polymer-host dye lasers, due to rather low thermal conductivity of polymer materials, arising, in particular, at flash la~p pumping and high repetition rates, are discussed. Some practical methods allowing to overcome these limitations are also discussed.

Novel resonators are developed and investigated that posses specific properties in point imaging. These resonators are the basis for construction of multicolor dye and solid state lasers generating in all the visible and near UV or IR.

We describe experimental results of cw laser operation using a red (670 nm) laser diode pumping two near-infrared dyes (Rd-800 and Rd-700). Red diode lasers operating with 300 mW cw power were characterized, paying particular attention to beam quality. Collimating optics and a highly astigmatic focusing system were designed and demonstrated, producing an approximately 50 micrometers diameter focal spot, resulting in over 15 kW/cm² pump intensity (per diode). The resulting diode/optical system was used to pump a commercial Coherent Model 599 cw dye laser utilizing a flowing dye jet.

A cw dye laser pumped by laser diodes has been demonstrated. Two 10 mW visible laser diodes were polarization combined to pump a rhodamine 700 dye jet laser. The absorbed pump threshold power was 5.6 mW and 0.28 mW of output power was produced at 758 nm. The resonator was scalable and generated over 360 mW with a slope efficiency of 57% when pumped with a DCM dye laser at 660 nm.

A number of techniques have been considered for reducing the divergence of the beam of energy generated by a flashlamp pumped dye laser, particularly for those lasers with a high Fresnel number. the principal motivation is to enhance the brightness of such laser beams. The techniques that have been evaluated, or are under active investigation, include: solvent effects; unstable resonators; telescopic resonators; oscillator amplifier configurations; and phase conjugation techniques. Results are presented that show that judicious choice of solvents can give a modest reduction in divergence and improvements of at least a factor two in beam brightness. More sophisticated techniques such as the use of a telescopic resonator can enhance the brightness by a factor in excess of 200. There is scope for further improvement in beam quality by suitable combinations of techniques or materials.

The pyrromethene-BF₂ (P-BF₂) complexes are a new class of efficient laser dyes that exhibit laser action from the green to the red spectral region. Some of these dyes outperform commercially available dyes, showing laser action in the same spectral region. We, therefore, are presenting experimental data on laser action efficiency under flashlamp, cw laser, and synchronously pumping of some typical P-BF₂ laser dyes. The main reason for the improved performance of the new laser dyes is reduced triplet state absorption over the fluorescence spectral region of the triplet state P-BF₂ molecules. Triplet state losses in laser dyes are briefly reviewed. Some general criteria for obtaining improved laser dyes are discussed. Because of the long triplet state lifetime (tau) _T of the P-BF₂ molecules in solution, these dyes do not yet exhibit maximum laser action efficiencies under flashlamp excitation.

Four new BF₂-complex laser dyes have been synthesized and spectroscopic and laser studies have been performed. The 8-cyano-pyrromethene-BF₂ complexes showed the best performance with red emission and slope efficiencies as high as 48% when pumped with a frequency doubled Nd:YAG laser. Additionally, three previously known pyrromethene-BF₂ complex dyes obtained from a commercial source were tested. These dyes showed a relative efficiency of greater than 80%, with one (PM-580) displaying a slope efficiency of 89%. This efficiency is the highest reported for any dye laser.

A polychromatic laser is constructed emitting comb-like spectrum in several bands simultaneously inside all the visible region of the spectrum. This laser is applied for development of a multicolor holographic spectrointerferometry method suitable for investigation of complex physical objects. Advantages of this method are discussed as a diagnostic of multicomponent plasma.

Spectroscopic and photocheraical properties of iodine molecule are of a great interest and they are under wide investigation C I J. Excitation and energy relaxation processes are to be studied for providing best conditions of plasma devices containing iod ing vapour. It is known that light absorbtion in the visible region of spectrum (400-650 rim) is connected generaly with transition into B-state.

High power visible semiconductor laser diodes are reported at wavelengths ranging from 620 nm to 690 nm. Broad area laser diodes exhibit peak cw output powers of 3.8 W from a 250 micrometers aperture at 688 nm and > 1 W cw at 636 nm from a 100 micrometers aperture. Monolithic 1 cm arrays with a 24% filling factor provide output powers of 30 W cw at 687 nm. Single mode lasers in the 620 nm wavelength band emit > 50 mW and operate at temperatures up to 80 degree(s)C.

We develop an automatic power control aging simulation method for AlGaInP visible light emission laser diodes and apply it to aging tests of 650 nm wavelength AlGaInP lasers. A laser degradation expression, on which the simulation is based, is derived from automatic current control tests for 680 nm lasers. The simulation results agree well with the experimental results. The simulation is then used to show laser reliability (operation lifetime) as a function of laser initial characteristics (threshold current, characteristic temperature and the maximum cw temperature).

The properties and low pressure organometallic vapor phase epitaxy of Ga_xIn_1-xP/(AlGa)_0.5In_0.5P quantum well (QW) laser diode heterostructures with Al_0.5In_0.5P cladding layers, and having a wavelength of 614 < (lambda) < 690 nm, are described. At longer wavelengths ((lambda) > 660 nm), threshold current densities under 200 A/cm² and efficiencies greater than 75% result from a biaxially compressed GaInP QW active region. Although short wavelength laser performance is diminished by the poor electron confinement afforded by AlGaInP heterostructures, good 630 nm band performance, and extension into the 610 nm band, is achieved with strained, single QW active regions.

Intracavity second harmonic generation with a three mirror folded cavity configuration was investigated with a flashlamp pumped, Q-switched Alexandrite laser. We therefore used different nonlinear optical crystals to convert the fundamental 750 nm radiation into the near UV spectral range (375 nm). The laser pulses were stretched into the microsecond(s) time domain by an electronic feedback system regulating the losses of the resonator. We investigated the conversion efficiency for different pulse lengths as well as the effect of pulse-lengthening due to the nonlinearity of the intracavity losses introduced by the optical crystal used. Working with BBO-crystals, we were able to achieve a second harmonic output of 25 mJ per pulse at 375 nm with a temporal rectangular pulse of 1 microsecond(s) in length and a stable nearly Gaussian shaped beam profile.