Role of chirp in spatiotemporal modulation instability of broadband pulsed laser

Abstract

We report on the theoretical derivation and experimental demonstration of the influence of chirpon the spatiotemporal modulation instability in a nonlinear Kerr medium. Based on a derived (3 + 1)-dimensional nonlinear Schrödinger equation for chirped laser pulse propagation, we obtainthe expression for the instability gain spectrum of a chirped laser pulse by using a standardlinear stability analysis. It is shown that the pulse chirp does not affect the instabilityregion and the fastest growth frequency. In the experiment, we observe the nonlineargrowth of spatial stripes with different modulation frequency due to the small-scaleself-focusing. We also obtain the gain spectra of the laser pulses with different values ofpulse chirp. It is found that, for the condition that the contributions of nonlinearity (Nnl) are equal, the experimental results are in agreement with the theoretical predictions.