Recent advances in lead salt laser design have resulted in significant increases in both continuous and discontinuous tuning ranges. The former improvement results from a reduction in lateral and circulating modes. The latter increase in total tuning range is a consequence of increased maximum operating temperatures. The importance of such improvements will be illustrated with analyses of stable and transient gas species as well as deuterated species of water.

Tunable diode lasers of lead-salt materials have been demonstrated to be a useful tool for trace gas analysis, high resolution spectroscopy and infrared astronomy studies. Only recently, applications such as optogalvanic spectroscopy, spectroscopy of molecules in solids and on surfaces, and industrial process control have been explored. This paper reviews the recent advances in tunable diode laser technology to achieve high temperature, single mode operation for these applications. The use of the molecular beam epitaxy technique for the fabrication of heterojunction structure, stripe geometry diode lasers will be emphasized.

High power tunable infrared radiation has been generated by difference frequency mixing in the non-linear crystals LiNb0₃ and AgGaS₂. A commercially available system in which one to ten millijoules per pulse in the spectral region of 1.5 to 4.5 microns is described. Also discussed is work being performed to extend the range of the instrument to 12 microns.

An overview of CO₂ laser technology in the 100-5000 Watt power range is presented. Included is a discussion of typical laser characteristics and a comparison of various design alternatives. Important current applications of these lasers are reviewed, and speculation as to potential uses in chemistry is given.

The term "color center" refers to a broad class of point defects in crystalline lattices. The name originated because many of these defects impart characteristic colors to the otherwise colorless pure crystals. Only a small fraction of the many distinct types of color centers exhibits laser action. The systems that do lase are all characterized by homogeneously broadened emission bands with high oscillator strengths and high quantum efficiencies. This leads to laser oscillators with large tuning ranges, high output powers and low threshold pump powers. As a class, color center lasers can tune continuously from 0.36 microns to 4 microns. To span this range requires the use of several different types of color centers as well as several members of each type. A single crystal may have a tuning range of from 500cml to 2000cml. The width of the tuning band and its wavelength peak depend strongly on the color center type and the lattice host, but there is very little variation among various samples of the same system. The shift of the tuning band among the various host lattices can be as small as 10% for the TI°(1) defect and as large as 100% for the F₂+_A defect. Almost all color center systems require cryogenic operation to achieve lasing. However, the best systems only require storage at 0°C to be free from any long term degradation effects, while the least desirable must always be maintained at liquid nitrogen temperatures even when not in the laser. Except for the requirement for cryogenic cooling, most laser cavity designs are quite similar to the techniques used for dye lasers. The maximum laser output power depends most strongly on the efficiency of the color center fluorescence and the Stokes shift between the pump and laser wavelengths. In turn, the fluorescence efficiency is a product of the quantum efficiency and geometrical factors relating to the pump and laser polarizations. The Stokes shift is additionally important because the fluorescent quantum efficiency decreases at elevated temperature. The larger the Stokes shift, the greater the fraction of the pump power that is dissipated as heat in the crystal. For F_A(II) systems with large Stokes shifts and temperature-dependent quantum efficiencies, the maximum obtainable powers are 50 to 200 mw, corresponding to an energy efficiency of 5 to 10%. For the F₂+ systems with fairly small Stokes shifts, output powers of several watts with efficiencies of greater than 60% have been obtained. Some color center systems degrade under the action of the pump laser, much as laser dyes experience photodegradation. Susceptibility to this process varies widely and the best representatives, the F_A(II), exhibit no measurable deterioration over several thousand hours of use. Other systems, such as F₂+, can degrade completely in a few milliseconds. Because color center lasers are solid state systems with no moving parts, they exhibit excellent intrinsic frequency stability. With careful engineering, color center laser systems can achieve narrow linewidths (< 1MHz) and low drive rates (< 1MHz/minute) even in passive, unstabilized operation. With active stabilization schemes, color center lasers have produced linewidths of less than 10 KHz and drift rates of 1 MHz/hour.

We review the current status of parametric oscillator tunable sources with an emphasis on progress in the past decade. Recent results are reported for the first OPO operated in a chalcopyrite crystal, AgGaS₂.

Excimer lasers are proven sources of high pulse energy and high average power coherent radiation at several wavelength regions throughout the ultraviolet spectrum. If designed properly, excimer lasers can be operated with both low divergence and narrow spectral band-width, and usingoan oscillator - injection-locked amplifier configuration they can be tuned over a 10 to 20 A bandwidth without appreciable loss in energy. Additional wavelength coverage from excimer lasers can be obtained by stimulated Raman scattering. With the development of magnetic switching for the high voltage, high power switches, the electric discharge exci-mer laser can also be operated reliably for extended periods of time at high pulse rates. All these features make excimer lasers ideal sources of ultraviolet radiation for a variety of remote and in-situ atmospheric species measurements.

The recent development of rare gas halogen excimer lasers as amplifiers for picosecond pulses has led to the availability of ultraviolet laser pulses with gigawatt peak powers [1,2]. As primary sources of ultraviolet radiation, these lasers provide new leverage for the nonlinear generation of extreme ultraviolet (XUV) coherent radiation. We report studies of harmonic generation using a picosecond pulse 24P nm krypton fluoride laser system [1]. The third, fifth, and seventh harmonics were observed at 82.P nm, nm, and 35. nm, respectively. A more detailed description of the experiments has been published elsewhere [3]. A new geometrical arrangement for the observation of harmonic generation to the XUV spectral region was employed in these experiments; the nonlinear interaction took place at the intersection of the laser focus with an orthogonally directed, pulsed supersonic gas jet [3,11]. such an arrangement provides a localized region of high gas density in the vicinity of the nozzle orifice while substantially reducing the gas load on the pumping system.

We describe the application of pulsed free jets for the generation of the third harmonic of laser radiation. Using a supersonic expansion of Xe we have frequency tripled an 18 MW beam at 354.7 nm to obtain 5 x 10" photons/pulse at 118.2 nm, while for CO we have obtained 1 x 10¹² photons/pulse at 98.5 nm for an input power of 2 MW at 295.6 nm. In the latter case the conversion efficiency is enhanced by a two-photon resonance via the CO A¹II state. A simple model is outlined for third harmonic generation in a free jet, and the predictions of this model are tested against experiment.

High spectral brightness KrF* (249 nm) and ArF* (193 nm) excimer laser sources have been used in a variety of experiments to test the generation of coherent short wavelength radiation (λ ti 100 nm) using nonlinear processes. These experiments include harmonic generation, sum frequency mixing, two and four photon pumping of lasers as well as spectroscopic application of such short wavelength radiation and the study of nonlinear coupling at intensities of up to ≈ 10¹⁷ W/cm².

In this paper we review the current state of Cr³⁺ doped solid state vibronic laser technology. Included in this overview are recent results on Cr³⁺ doped beryls, garnets, and perovskites, and on co-doped Cr³⁺:Nd³⁺ activator-sensitizer lasers.

Characteristics of the alexandrite laser medium are reviewed. Performance features of several previously developed alexandrite lasers are presented. Methods are discussed for shifting alexandrite emission into other wavelength bands via frequency conversion. Alex-andrite's suitability is specified for applications in photochemistry, remote sensing, and material processing. Examples are given of alexandrite technology considered to be present state of the art.

The scaling of solid state lasers, in size and average power, is limited by the thermal dissipation of the unused input pump power. In order to remove the waste heat, the host material must be cooled, which induces thermal gradients and stress in the active medium. If the rod geometry is used, the thermal gradients quickly gives rise to deleterious optical effects. In the slab geometry,¹ however, the thermal gradients only affect the optical beam in second order. Therefore, substantially higher average powers, with good beam quality, are possible.

Recent experimental demonstrations of free-electron laser oscillators are attracting the attention of research and industrial chemists. We review the inherent properties of these photon sources, the operating parameters of successful oscillators, and potential chemical applications.