Stable operation of a powerful 3-Hz line-tunable TEA-CO2 oscillator-amplifier system

Abstract

We report a medium-repetition-rate, highpeak-power CO2 oscillatoramplifier chain producing 10.6 m pulses of up to 1014 W/cm2 for use in intense-laser-interaction experiments. It has a simple provision for reducing retroreflections. Parasitic oscillation and amplified back reflections are deleterious phenomena often associated with high gain laser amplifier chains. Because the gain duration of atmospheric amplifiers is relatively long, a long optical delay (about 50 m or more) is installed to reduce the amplifier gain before any back-reflected energy maybe amplified.1 Electro-optic crystals, plasma switches, or saturable absorber gas are often used to isolate the reflection. The latter method is the simplest. It depends on the relaxation time of the gas. A popular choice of SF6/He is not sufficient. We found that SF6:C2H6::5:760 mixture takes only 11 ns to relax.2 Situating such a saturable absorber cell in the amplification chain, therefore, substantially reduces amplified retroreflections without the need for high pressure gain modules or optical delays, and it simultaneously provides contrast enhancement. Our laser now routinely operates at 3 Hz, 1 ns, and 1 J/pulse for experiments on tunnel ionization of atoms and molecules.