Recent tests confirm that commercially available excimer lasers meet most industrial requirements including the most strenuous - continuous constant power operation at maximum specified power ratings. Test results include lifetime data plus the determination of maintenance and operating costs. A few proven industrial applications are reviewed as well as the field experience on their production lines. The field and test data compare favorably.
Industrial applications of excimer lasers are expanding rapidly. This trend has led to the evolution of a new generation of excimer lasers designed specifically for industrial usage. This paper reviews some of the issues which need to be addressed in the development of such a laser. Included are market considerations, technology related items and issues related to the laser configuration.
Industrial applications for excimer lasers are developing at an increasing pace, and users are defining the laser requirements for these applications. At the same time, excimer laser manufacturers are responding with lasers intended to meet these requirements. There is a strong tendency, however, for manufacturers to offer existing or slightly modified general purpose "scientific" lasers, rather than develop entirely new lasers. Such an approach is risky because users demand far more than can be delivered by "scientific" designs. A far better approach is to consider the laser as part of an industrial system, define the laser requirements for this system, then design a laser to meet these requirements without the constraints of existing designs. This paper describes the steps Questek has taken to define and develop industrial excimer lasers.
Laser sources based on the diatomic sulfur (S2) molecule have demonstrated features which make this molecule an attractive tunable laser alternative. The very high gain on the S2 B--X transitions allows superfluorescent laser emission over a broad spectral range, from the UV to the orange. The lasing medium may be contained in a sealed-off optical cell practically indefinitely, thus eliminating the need to regularly replace gases, dyes, or solvents. The S2 molecular vapor is easily and fairly efficiently pumped by standard xenon chloride (XeClJ UV excimer lasers. Pumping by other UV laser sources (N2, He-Cd) produces Raman spectra which provide additional output wavelengths in the UV and visible. The work summarized here deals with the operation of a superfluorescent S2 laser wavelength converter. This device has achieved up to 211 simultaneous laser lines in groups from 328 to 583 nm in a thermal dissociation configuration with 308 nm excitation from a xenon chloride (XeC1) laser. Due to the superfluorescent operation of this device, the overall conversion efficiency is low, although it has been observed to be as high as approximately 10%. In order to understand the operation of this wavelength converter, a range of experiments was performed which involved sulfur molecular dissociation kinetics and optical absorption measurements, as well as spectroscopic emission/ absorption band origin identification. These data also lead to measurements and estimates of laser operational parameters.
Experiments in which epitaxial semiconductor films (Ge) have been grown by laser photochemical vapor deposition (LPVD) are described. The results provide a clear example of the ability of LPVD to grow epitaxial films under conditions in which growth is not attrib-utable to substrate heating or adlayer photolysis but rather to species generated photochemically and in the gas phase.
The evolution of the excimer laser from a research tool in the 1970's to the industrial models of the 1980's has opened up numerous applications in semiconductor manufacturing, corneal surgery genetic research and material processing in many fields. Microprocessor controlled laser systems, including computer-controlled delivery systems, will now run for up to 50 million shots before undergoing scheduled maintenance. The energy is delivered to a tolerance of +10% in most cases. While many uses for the excimer laser are still research oriented, the production applications are rapidly emerging. The continued reduction of VLSI circuit geometries together with increasingly higher levels of circuit integration create the demand for new circuit fabrication technologies. One of limitations of current IC fabrication technology is the use of high temperature processing. High temperatures distort silicon wafers, causing loss of resolution and alignment control and a subsequent reduction of device yield. Excimer laser technology, at very short ultra-violet wavelengths, offers the possibility of low temperature processing, including the following major applications: Photoresist exposure, photoresist ablation over alignment marks, annealing and doping, and etching. In addition, applications in IC packaging, circuit personalization and fiber optics appear as very promising new applications for excimer laser technology in the electronics industry.
The physical and chemical degradation of dielectric materials in excimer lasers is generally considered to be one of their primary lifetime limiting factors. Adverse chemical, radiation, thermal, and mechanical environmental factors coupled with the high costs when scaling to multijoule output energies has prompted feasibility testing of new dielectric materials for use in large discharge pumped XeC1 systems currently under development. Glass-filled polyphenylene sulfide (hereafter referred to as PPS) is a modern thermoplastic possessing a number of desirable mechanical and electrical properties that has prompted an investigation for it's use as a dielectric and structural material in x-ray preionized, discharge-pumped XeC1 lasers. Teflon and Kynar, which had been used previously in a number of designs, have good resistance to chemical attack in the discharge environment and good electrical resistance properties, but are mechanically less desirable and can be very costly to incorporate into large, multijoule excimers because of difficulties in their fabrication. PPS is also quite resistant to attack by the active components of XeC1 laser gas, possesses superior mechanical properties to either Teflon or Kynar and is much less costly to incorporate into existing designs.
Several novel diagnostic techniques have been used to analyze the laser kinetics occurring in electron-beam pumped excimer lasers. Described are a quadrature interferometer for measuring time-dependent electron densities, an overtone absorption technique for measuring the HC1 concentration, a broadband dye laser system for measuring the spectrally resolved gain in XeF, and a hook interferometer for measuring time-dependent excited state densities. These techniques can also be applied to other non-excimer lasers.
The XeF(C->A) excimer laser is an efficient, scalable gas laser that is tunable throughout the blue-green region of the spectrum. Recent wavelength tuning experiments will be reported using a long pulse quasi CW dye laser as an injection source. Also the effect of electron-beam energy deposition on laser performance will be discussed. 1. INTRODUCTION The electrically excited XeF (C->A) excimer laser is wavelength controllable by injection techniques and has the potential for a relatively high intrinsic efficiency ,. Using a coaxial flash lamp pumped dye laser as the injection source, amplified output pulses tunable between 470 and 500 nm and having a spectral width of 0.6 nm were obtained. It was found that previously reported electron-beam induced transient absorptions appear to be saturable through the use of an intense injection laser pulse .
The spectroscopy and chemical kinetics of small molecules known (or believed) to absorb in rare gas-halide laser plasmas are being studied by laser excitation and probing tech-niques. Two examples from recent experiments -- inter-Rydberg absorption spectroscopy of Art and photoassociation (bound 4- free absorption) of Kr-F collision pairs -- are described.
Abstract Rare-gas halogen excimer lasers which emit in the middle and near ultraviolet have been shown to make extremely clean, sharp cut s in tissue with little thermal damage to nearby tissue. In addition to their high absorption and short pulsewidth that result in minimal tissue damage, it is believed that the high photon energies of these ultraviolet wavelengths also result in chemical bond breaking during the ablation process. This paper reviews the current status of ultraviolet lasers in medicine, examines the ongoing research and discusses the problems that remain.
Excimer Lasers represent the shortest wavelength lasers currently available for fieldable laser radar systems. Since the imaging resolution of a laser radar is directly proportional to its wavelength, considerable interest in excimer based laser radar has been generated in applications where high resolution imaging is required. In this paper we review some of these applications, the resulting laser radar transmitter and receiver requirements, and possible excimer radar configurations based on presently available technology.
A collinear acousto-optic tunable filter (AOTF) is used to achieve all-electronic, rapid wavelength tuning (agility) of a pulsed CO2 laser. Electronic intra-cavity laser wavelength selection is demonstrated on both the P and R branches of the (0001) - (1000) CO2 band. An intra-cavity AOTF greatly expands the flexibility of a CO2 laser affording 10-50 kHz wavelength switching rates, allowing broad-band (9-11 μm) coverage and random wavelength access, and is basically rugged. This paper covers a description of wavelength tuning by the AOTF mechanism, design and fabrication steps of the collinear AOTF, problems encountered, and test results.
This paper reviews the spectral purity, frequency stability and long-term stabilization of CO2 isotope lasers developed at MIT Lincoln Laboratory. Extremely high spectral purity and short-term stability of less than 1.5 x 10-1' have been achieved and will be discussed. A long-term stabilization technique, which was used to line-center lock any regular or hot-band CO2 isotope laser transition, is described. A brief description on using CO2 lasers as secondary frequency standards is also given.
To study second harmonic generation in nonlinear crystals it is important to have a versatile laser driver which can produce high-power variable pulse widths at a single frequency which is adjustable over both the 9 μm and 10 μm laser bands. To satisfy these requirements, a nominal 5 J UV-preionized self-sustained discharge TEA CO2 laser has been designed to give 100 ns 9.6 ism pulses at 2 Hz. The laser is a line-tunable oscillator-amplifier design with a pulse width which is adjustable from "3 to 250 ns.
A transverse-discharge copper-vapor laser (TD-CVL) has been operated at high repetition rates in a steady state mode for an extended period of time. In an unoptimized operation at 1 kHz, an average power of 560 mW was achieved in an excited volume of approximately 40 cm3. It is now feasible to develop TD-CVL systems that can be discharge-heated like conventional longitudinal copper-vapor lasers.
The Copper Vapour Laser (CVL) is an efficient ("1%) source of pulsed high power visible laser light in the green (511nm) and yellow (578nm) region of the spectrum. We present results which characterise the performance of a three laser CVL system designed to produce over 90w of visible power with 90% of this output having a full angle divergence of less than 400 microradians. The total output power and output power within 400μ radians of an Injection Controlled Oscillator (ICO) have been measured as a function of injection timing. The power extracted from a 60W lasers (CU60) acting as a single pass amplifier was also mecLs,..veci as a function of its timing. Laser pulse shapes of the total output and within 400 μ rads are shown both for the ICO and the entire system. Measurements have also been made of the small signal gain and saturation fluence by probing with narrow beams both at the edge and on the axis of the final amplifier stage of the system.
Thyratrons tend to latch in the capacitor transfer circuit of our low impedance copper vapor laser. This is due to impedance mismatch between the laser plasma and the operating circuit, which causes a large returning inverse pulse from the laser head back to the circuit. The cause of the latching is explained in detail and a new circuit to overcome this problem without changing the input to the laser head, is described.
Burst-mode experiments and observations of evolving radial profiles of amplified spontaneous endlight and small-signal gain in a Sr+ laser are discussed with a view to prospects for scaling the average output power of Sr+ (430.5nm) and Ca* (373.7nm) recombination lasers to multiwatt levels.
I present a novel procedure that uses Krypton gas for laser processing. This includes new tube processing and used tube reprocessing of air-cooled argon lasers. I will explain the dynamics involved in laser tube outgassing and saturation. The use of krypton as a preprocessing discharge gas effectively reduces processing time. I present a novel flow-through processing method. I also describe a novel approach which induces accelerated gas clean-up rates. The processing time for new and used tubes reduces from 3 days to 1 day.