Optimisation of the pulse duration of a discharge-pumped XeF( <Emphasis Type="Italic">BX </Emphasis>) excimer laser

In an x-ray preionised XeF(B~X) dischargeexcited laser driven by a magnetic-spiker sustainer circuit with a magnetic pulse compressor the influence of the various parameters on the optical pulse duration was experimentally investigated. Laser pulses at 2= 351 nm with a duration of 212 ns (FWHM) have been achieved in a NF3/Xe/Ne mixture by using very low (0.25 mbar) NF3 partial pressures in a total gas pressure of 2.5 bar and with a high-reflecting output coupling mirror. PACS: 42.55.Gp; 42.60.By; 52.80 In recent years long optical pulse discharge excited excimer lasers became of practical and scientific interest. The low peak power associated with long-pulse operation permits greater laser energy transfer through fused silica fibers, making these lasers attractive sources for medical applications. In addition, the increased number of cavity round-trips times provided by long-pulse operation permits the control of the laser divergence, line width, polarisation, and level of amplified spontaneous emission. There are a number of factors such as the electrical circuit, halogen concentration, total pressure, output coupling mirror transmission and electrical energy deposition which influence the rare-gas halide laserpulse duration. Recently, the use of magnetic-spiker sustainer excitation circuits for XeC1 rare-gas halide lasers has resulted in a higher efficiency, longer optical pulse durations and higher beam quality compared to conventional electrical discharge excitation circuits [1-3]. The magnetic-spiker sustainer technology also has been used to achieve long optical pulse KrF (170 ns) [1] and KrC1 (185 ns) [4] laser operation. Spiker-sustainer circuits [5] comprise of two electrical circuits. A highimpedance, high-voltage spiker circuit and a low impedance sustainer circuit which deposits the main part of * Permanent address: Institute of Electronics, Academia Siuica, Beijing, P.R. China the stored energy into the discharge. The spiker circuit provides a fast rising voltage pulse to increase the electron density from its preionisation value to its quasi steady-state value. Once the discharge has been ignited the sustainer circuit can deposit the energy efficiently into the discharge under impedance-matched conditions. In magnetic-spiker circuits [6, 7] a saturable inductor provides the electrical insolation between the spiker circuit and the sustainer circuit. In this paper we report on the achievement of long-pulse laser emission from an x-ray preionised XeF(B~X) discharge excited laser (2 = 351 nm) driven by a magnetic-spiker sustainer circuit with a magnetic pulse compressor. The influence of the various parameters on the optical pulse duration was experimentally investigated. Results are presented on the operation of a long-pulse-duration gas discharge XeF(B---,X) laser using the resonant overshoot mode. The longest measured optical pulse duration (FWHM) was 212 ns. Experimental setup The laser chamber used in the experiments is a highpressure stainless-steel vessel. A 60 cm long high-voltage electrode of Ni coated aluminum is mounted above a ground electrode made out of a stainless-steel plate. The gap between the electrodes is 2.5 cm. The active volume is 60 cm (L) x 1 cm (W) x 2.5 cm (H). The discharge volume is preionized by a cold-cathode x-ray source. The cathode (made of carbon felt) is separated 2 cm from a Ta-foil anode operating in the transmission mode. The Ta-foil is mounted on a thin aluminum plate which separates the high-pressure laser chamber from the evacuated x-ray source. The optical resonator consists of a flat dielectric output mirror with either 10%, 30% or 50% transmission and a concave (R = 5 m) dielectric total reflector. The distance between the mirrors or the cavity length is 130 cm. The temporal behaviour of the optical pulse is detected by a silicon photo diode (EG & G FND 100 Q). The dis-