High power excimer lasers which can deliver average powers of 100 W or more have been commercially available since 1983 when Lambda Physik introduced its model EMG 203 MSC. This progress was the result of a new proprietary switching technique (Magnetic Switch Control or MSC) which allowed unprecedented control of the energy flow through the high voltage discharge circuitry. In conjunction with a carefully designed gas flow and the judicious choice of components, this technique has meanwhile enabled the design of a large variety of reliable excimer systems including injection locked systems, lasers which deliver 120 W average power and lasers which can operate at up to 1000 Hz pulse repetition rate.

We review the work at Los Alamos regarding long pulse excimer laser operation using the technique of inductive stabilization of avalanche discharges. This technique, depending on the rate of energy deposition, has allowed laser pulse lengths of greater than 120ns and total lasing times greater than 200ns. Small lasers employing this technique are particularly useful in the control of large amplifiers to obtain narrow linewidth, near diffraction limited operation as well as in the amplification of mode-locked pulse trains to further enhance the brightness of the laser system. The performance of small lasers with short cavity length used for narrow-band frequency tuning, active modelocking and the advantages associated with high repetition rate operation will be discussed. The scaling to longer gain lengths and to high average power systems will also be discussed. Finally, a brief discussion of the potential uses of small long pulse devices in the areas of high brightness sources, medical and semiconductor applications will be given.

The charcteristics of strongly saturated amplifier with a 100ns electron beam excitation are studied to determine the small signal gain, non-saturable absorption, and saturation intensity from 6% Kr to 95% Kr in Ar diluent. The pumping rates are maintained constant by adjusting the total pressure of gas mixtures to conpensate the different stopping power of Ar and Kr. Non-saturable absorption coefficients are measured at a full saturated amplifier between the zero gain intensity to 80MW/cm2. The small signal gain of 12.9%/cm and non-saturable absorption coefficient of 1.32%/cm2 are obtained for 95% Kr mixture. The saturation intensity, 2.2MW/cm2 for 6% Kr and 2.9MW/cm2 for 95% Kr mixture, derived from the zero gain intensity is in good agreement with the prediction of our computer model. Highest intrinsic efficiency of 12.2% is measured at high Kr concentration where the Extraction power density of 6.8MW/cm2 is obtained by the probe laser beam between 5-6MW/cm2. The formation efficiency for a wide range of Kr concentrations agrees with the theoretical prediction excellently as a function of Kr concentration. The details of the important parameters, gain , absorption, saturation intensity, maximum output, intrinsic efficiency, extraction efficiency, and formation efficiency will be discussed in this paper.

Important goals in DOE and DoD programs require multimegajoule laser pulses. For inertial confinement fusion there is also a requirement to deliver the pulse in about 25 nsec with a very particular power vs time profile-all at high overall efficiency and low cost per joule. After exhaustive consideration of various alternatives, our studies have shown that the most cost effective approach to energy scaling is to increase the size of the final amplifiers up to the 200 to 300 Id level. This conclusion derives largely from the fact that, at a given complexity, costs increase slowly with increasing part size while output energy should increase dramatically. Extrapolations to low cost by drastic cuts in the unit cost of smaller devices through mass production are considered highly risky. At a minimum the requirement to provide, space, optics and mounts for such systems will remain expensive.

Picosecond amplification characteristics were investigated in KrF amplifiers with aperture sizes of 2xlcm2 and 7x7cm2. The system including a ps pulse generator, two 2xlcm2-aperture lasers and a 7x7cm2-aperture laser was successfully operated with the precise synchronism, resulting in an output energy of 150 mJ.

Fundamental aspects of pulsed laser melting and solidification of crystalline silicon and germanium are reviewed. The discussion concentrates on time-resolved experiments performed with nanosecond pulsed lasers, although some picosecond and femtosecond experiments are also considered. The creation of amorphous material from crystalline material induced by ultrarapid melting and resolidification using either nanosecond or picosecond lasers is surveyed and the inverse process of recrystallization of a-Si by explosive crystallization is described. Finally, melting model calculations, which have proven to give a very accurate description of the pulsed laser irradiation process, are discussed.

This paper reviews the rapidly emerging field of excimer laser lithography. Beginning with the first contact printing experiments, developments in excimer laser projection printing on various commercial lithographic machines are reviewed. Recent results obtained with full-field scanning projection systems as well as step-and-repeat tools are summarized. Future directions in optical lithography are examined in view of these advances. Finally, a discussion of various key excimer laser parameters is presented from two points of view: availability, and requirements for various practical lithographic systems.

A brief overview of the status of laser photochemical vapor deposition (LPVD) will be given, with emphasis on large area processing. Recent experiments, in which chemical vapor deposition of Ge (or Si) has been "triggered" by ultraviolet (UV) laser photodissociation of GeH4 (or Si2H6), are described.

Bombarding solid surfaces with intense 248 nm KrF* or 193 nm ArF* excimer lasers leads to rapid etching. The ejected material consists of atoms, diatomics and larger clusters. Using laser fluences near threshold so as to minimize perturbations due to gas-phase collisions and to laser-produced plasma, the energy distributions of the first two types of species were measured by laser-induced fluorescence (LIF). The species detected were Al, A10, C2 and CN. The results show that for a metallic-like material (graphite) the energies agree with a purely thermal mechanism for the vaporization. In distinct contrast to this, insulating materials (sapphire and polymers) display nonthermal energy distributions and point to a photochemical (bond-breaking) mechanism. Understanding these mechanisms is of interest to microelectronic circuit production techniques, to optical damage prevention, and to laser surgery.

Excimer lasers are finding increasing use in both semiconductor and materials processing. In the semiconductor area, this has led to the development of excimer based processes for lithography, film deposition, etching, doping and annealing. In materials processing, the unique capabilities of the excimer laser offers the potential for greatly extending the range of laser based cutting, drilling and marking techniques. This paper is intended to provide an overview of these areas. Attention is given to the means by which the excimer laser addresses the critical needs in each particular case.

Over the past decade, laser processing of semiconductors has developed into an area of widespread interest in solid state physics, materials science, and semiconductor device technology. Initially, most of the work on pulsed laser processing was carried out with solid state lasers such as ruby and Nd:YAG lasers. These lasers have several inherent characteristics that make them less than ideal for studies of laser processing and that would seemingly prohibit their use in many commercial applications. More recently, results which demonstrate that ultraviolet excimer lasers offer many desirable characteristics for the laser processing of materials, have been reported in the literature. Solar cells are relatively simple semiconductor devices that are of considerable interest in their own right and provide a useful testing ground for the application of laser techniques to semi-conductor processing. In this paper, some important aspects of pulsed laser processing of semiconductors are reviewed, the advantages of excimer lasers for such work are assessed, the present status of laser processing of high-efficiency solar cells is discussed, and finally the possible future directions of this type of work are briefly mentioned.

Laser damage threshold measurements in the ultraviolet' (UV) have been made at the Lawrence Livermore National Laboratory (LLNL) since 1979. These tests were conducted using single pulses at the third (355 nm) and fourth (266 nm) harmonic wavelengths of 1064-nm Nd-glass lasers, and single and repetitively fired pulses from KrF (248 nm) and XeF (351 nm) excimer lasers respectively. Surface damage thresholds of dielectric thin films, antireflective (AR) coatings, highly reflective (HP) coatings, and porous and graded-index AR coatings, as well as surface and bulk thresholds of optical windows and crystals have been measured. More than twenty different parameter studies have been conducted to develop materials with increased laser damage thresholds.

The development of truncated stimulated Brillouin scattering (TRUBS) as a means of producing subnanosecond laser pulses is described. Recent experiments carried out with a frequency doubled excimer-pumped dye laser system, incorporating a single longitudinal mode oscillator, and a single stage of amplification in a XeCℓ gain module have yielded subnanosecond (-100 ps) UV pulses with an energy of -2 mJ as well as lower energy pulses shorter than 50 ps. The technique shows considerable promise as a reliable means of obtaining excimer laser pulses in the 10-50 ps range.

Amplification in a XeC1 excimer gain module of 200-fsec UV pulses derived from a colliding pulse mode-locked (CPM) laser system was achieved, and the system producing the pulses was fully characterized. In an auxiliary experiment, the pulse width of -2.4-μm pulses generated by Raman shifting the 200-fsec UV pulses in Ba vapor was measured to be -160 fsec.

A subpicosecond excimer laser source with 30 GW peak power has been developed. The interaction mechanism at a laser intensity of up to 1016 W/cm2 has been studied using ion and electron time of flight techniques.

A picosecond 248 nm KrF* laser system producing a focal intensity of greater than 1015 W/cm2 has been used to study VUV fluorescence and harmonic generation in H2, He, Ne,'Ar, Kr, and Xe. The nonlinear media were found to fall into two distinct classes: the lighter materials, H2, He, and Ne, which readily support the generation of harmonic radiation, but do not fluoresce, and the heavier materials, Ar, Kr, and Xe, which produce significant amounts of fluorescence, but in which the generation of harmonic radiation decreases rapidly with the scattering order.

Recent experiments are described in which the electronic excited state structure of the rare gas dimers (Rg2), the triatomic rare gas-halide molecules Kr2F and Xe2Cℓ, and the heteronuclear KrAr have been studied in absorption or by laser induced fluorescence. One key aspect of these spectroscopic experiments is that the excited states are probed near their equilibrium radii. Measurements of the absolute photoionization cross-sections for the lowest lu, OU states of Kr2 and Xe2 are also discussed.

Published work on narrowbanding excimer lasers deals primarily with low energy, short pulse discharge lasers.1-3 In this paper we describe the narrowband (<200 MHz) operation of a large e-beam pumped excimer laser at Western Research Corporation (WRC). Narrowband laser pumping is required for cross-beam Raman conversion, a scaleable technology which promises to produce very high energy, high quality laser output beams.4 The narrowband system comprises a low energy frequency doubled dye laser front end, a 10 liter e-beam pumped intermediate amplifier, and the multi-kilojoule output SLAM laser. The excimer system operates with XeC1 at 308 nm and has produced a narrowband output of approximately 3500 J in a 630 ns pulse. In the following sections, we describe the SLAM laser and then detail the design and operation of the narrowband system.

Efficient, ultra-narrow spectral output from an electron-beam excited XeF(C+A) laser medium has been achieved by injection controlled tuning. Using a two-component buffer gas comprised of Ar and Kr, XeF(C+A) laser pulse energy and intrinsic efficiency values comparable to those of UV rare gas-halide lasers have been demonstrated. For a 482.5 nm injection wavelength that is well matched to the XeF(C+A) gain maximum, output energy density and intrinsic efficiency values of approximately 8 J/liter and 6% were achieved.

Long pulse excimer lasers are of interest as a means for increasing, with constant energy, the impulse coupled to a target. The reduced power associated with the long pulse width also increases the laser optics damage threshold. A direct e-beam pumped XeC1 laser has been operated with a 5 p's pulse length. The e-beam pump is a cold cathode, large area diode which has operated up to 10 μs pulse width. Fuel burn-up of the halogen donor occurs at approximately the same specific pump energy (J/ℓ ) observed with microsecond pulse lengths.