Pulse compression for more efficient operation of solid-state laser amplifier chains II

In a previous letter we proposed a compression scheme which reduces the intensity of a laser pulse in an Nd:glass amplifier chain and thereby allows more efficient energy extraction. In this scheme the nonlinear index of refraction (n
2
) of the glass in the amplifier impresses a frequency sweep or "chirp" on the pulse. Further analysis is presented here. The stability to amplitude noise is demonstrated. We calculate that impressed periodic amplitude modulation is responsible for the growth of distinct spectral sidebands in the nonlinear host glass, and we find that the compressor converts these sidebands into temporal features which precede and follow the central compressed pulse. When a pulse with 10-percent peak-to-peak impressed periodic modulation passes through a sufficient length of glass so that the peak nonlinear phase is approximately 4π, these precursors are only about 1/20th the intensity of the main compressed pulse. RMS equivalent random noise has a flat sideband spectrum, and the precursors are found to be absent in the compressed pulses. The intensity averaging over possible transverse-mode structures is studied for some axially symmetric spatial mode shapes. This averaging somewhat reduces the compression ratio from the estimates in which the transverse modes were flat-topped. Finally, arguments are presented to explain why it is felt that a grating pair is not likely to be a suitable compressor for such intense nanosecond-duration pulses.