Pulse Self-Compression in the Nonlinear Propagation of Intense Femtosecond Laser Pulse in Normally Dispersive Solids

Abstract

The self-compression phenomena of intense femtosecond pulses in normally dispersive solids were investigated experimentally. Both un-chirped and negatively chirped laser pulses were used as input pulses. It is demonstrated that intense femtosecond laser pulses can be compressed by the nonlinear propagation in the transparent solids, and the temporal and spectral characteristics of output pulses were found to be significantly affected by the input laser intensity, with higher intensity corresponding to shorter compressed pulses. By the propagation in a 3mm thick BK7 glass plate with the laser power of GW level, a self-compression from 50 fs to 20 fs was achieved, with a compression factor of about 2.5. However, the output laser pulse was observed to split into two peaks when the input laser intensity is high enough to generate super-continuum and conical emission. When the input laser pulse is negatively chirped, the spectra of the pulse are reshaped and narrowed due to strong self-action effects, and the temporal pulse duration is found to be self-shortening. With the increase in the input pulse intensity, the resulted self-compressed pulses became even shorter than the input laser pulse, and also shorter than sech2 transform-limited pulse according to the corresponding spectra.