Gas laser rf power source apparatus and method

Abstract

A gas laser RF power supply has two RF oscillators operating at different frequencies, the first frequency to provide maximum RF voltage to the plasma tube prior to ignition, and the second frequency to provide optimum power for sustaining CW or pulse operation of the laser. The oscillator outputs are modulated to control power to the tube, the one in the form of RF pulses at the first frequency and at a power level below the laser emission threshold, and the other in CW or pulse form at the second frequency at a laser gas medium excitation level above the laser emission threshold. The first frequency is the resonance frequency of the tube prior to plasma ignition and the frequency of minimum average RF power required for a reliable ignition. The second frequency is the most efficient operating frequency for the plasma ignited and kept ionized by the pulses of the first frequency and provides maximum output laser power. The pulses of the first frequency have a width, repetition rate, and amplitude sufficient to obtain a reliable ignition and sustain a level of the laser gas medium excitation below the laser emission threshold and are also adjustable to compensate for variations in the laser emission threshold for a particular tube-resonator combination. The oscillators may have a fixed or adjustable frequency. The RF amplifier input is switched between the outputs of the two oscillators by switching logic which also couples to a source of main laser power control pulses which inhibit the modulated RF pulses of the first frequency when the main pulses are present and which are also used to modulate the RF pulses of the second frequency to obtain the desired laser output power.