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A Compact CO2 Amplifier Optically Pumped by a Tunable 4.3 �m Fe:ZnSe Laser


There is currently an ongoing worldwide effort to develop long-wave infrared (8-14 �m) sources with GW-level peak powers and ~1 kHz repetition rate for HHG generation as well as TW-level peak powers for particle acceleration and for long-distance atmospheric propagation. CO2 lasers can store a great deal of energy and have been demonstrated to amplify 9-10 �m picosecond pulses to very high peak powers. However, the electric discharge typically used for pumping limits these systems to low repetition rates and small aperture beams because of the complexity of the large-scale high-voltage devices used for pumping and the difficulty in maintaining a stable discharge across large apertures at the high pressures (>10 atm) required for short pulse amplification. In principle, optically pumped CO2 lasers offer a compact alternative without these limitations, but the historic lack of high-energy pump sources at the appropriate wavelength has inhibited the study of picosecond pulse amplification in such a gain medium.In this thesis, we first present a detailed analysis of 10 �m lasing and gain dynamics in a CO2 medium optically pumped at ~4.3 �m by a continuously tunable Fe:ZnSe laser system. We then show that lasing can be achieved in a 6 cm long CO2-He cell at total pressures up to 15 atm by tuning the pump wavelength far from the peak of CO2 absorption. The optimization of experimentally measured CO2 vibrational temperatures allows optical-to-optical conversion efficiencies of up to 30% to be reached at atmospheric pressures, falling to ~5% at pressures above 10 atm. At these high pressures, the gain lifetime is measured to be ~1 �s, indicating the possibility of building both multi-pass and regenerative amplifiers using an optically pumped CO2 medium. Numerical simulations based on density matrix formalism confirm that the amplification of a 3 ps pulse and a sub-picosecond pulse to GW-level powers is feasible in such a compact high-pressure optically pumped CO2 amplifier.

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