Planar waveguide CO2 laser amplifiers
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The scaling of diffusion-cooled planar waveguide carbon dioxide laser oscillators to very high average power levels (> 5 kilowatts) is limited by mechanical constraints, associated with the physical size of the laser electrodes. Moreover, the operation of such lasers in pulsed mode is limited to pulse duration larger than - 50flS. However, there are important laser applications, for example in material processing, where the requirement is for high peak power level and short pulses combined with high average power. The principal objective of this project is to investigate a laser architecture based on the master oscillator power amplifier concept, but involving planar waveguide gain medium structures. Such an amplifier system may be used either for simple power amplification (long pulse/cw) or for amplifying short pulses using a 'pulse forming' modulator at the input for the amplifier. The laser excitation method involves transverse radio frequency discharges designed to match the large area slab-like structures. This excitation technique would permit multiple "stacked" slab operation with a single power generator, and in the future, may facilitate an "integrated" MOPA construction. The gain and power amplification characteristics of RF discharge excited planar waveguide amplifiers have been investigated over a range of operating parameters (gas pressure, RF power density, input beam intensity etc.) for both pulsed and cw input beams and also for single and multiple (folded) passes of the planar amplifier. Short pulses at the input to the amplifier ('p ~ 1 flSec) were generated using a long pulse oscillator and an acousto-optic modulator as a pulse slicer. In all cases, beam transformation optics were designed and utilised to ensure the excitation of the fundamental waveguide mode with minimal mode coupling. Studies of discharge-induced mode matching effects (phase shifts, amplitude variations) have also been conducted, and techniques for the elimination of parasitic oscillation have been developed. The future potential for the MOP A concept utilising this technology is evaluated for high power laser applications.