Abstract

A broadband chirped nanosecond pulse was propagated to a target. Compressing the return pulses to their Fourier transform limit enabled us to obtain sub-millimeter surface resolution of the target. The pulses used for this experiment were obtained from a Ndrglass based CPA system which had an uncompressed chirped time duration of 1.2 ns with 400 mJ of energy and a rise time of one nanosecond. The pulse had a compressed pulsewidth of 400 fs with 250 mJ of energy and a rise time of 300 fs. To obtain the highest spatial resolution possible, it was desirable to propagate the 400-fs pulse to the target. However, as the critical power for self-focusing in air is 3 GW, the peak power of this pulse was large enough to cause small scale beam filamen- tation after 10 m of propagation. Self-focusing would not develop if the uncompressed pulse propagated in air because its power was 10 times below the critical power.

© 1994 Optical Society of America