Backscatter of CO2 laser light from an overdense Z-pinch plasma

A mode-locked train of CO2 laser pulses, 2.5-nsec wide with 14.6 nsec between pulses, has been focused into an overdense Z-pinch plasma at vacuum intensities up to 2×1012 W cm−2. Backscatter through the f/5 lens has been observed to grow from a large noise level which is not present in the absence of the laser, and saturate at a value ∼ 4%.