Nonlinear spectral filtering of short laser pulses induced by phase and amplitude irregularities

Summary form only given. We demonstrate how a phase and amplitude irregularity, introduced to a Fourier transform-limited pulse by propagation in a weak narrow-line absorber, can strongly affect two-photon absorption of that pulse in a continuum absorber. Surprisingly, the continuum nonlinear absorber becomes almost transparent at the peak frequency of the discrete absorber, due to the combined effects of nonlinear absorption and index of refraction. While we take advantage of naturally occurring absorption lines, similar results could be obtained using artificial absorbers (e.g. quantum well excitons). In the experiment we used high-energy (typically 2 /spl mu/J) laser pulses of /spl sim/50 fs duration. The samples are 500 /spl mu/m thick wafers of GaAs and a 6 mm thick optical glass window.