Femtosecond Pulse Shortening using Cascaded Quadratic Nonlinearities for High Temporal Contrast

Recently, femtosecond pulse shortening techniques applicable for high peak power (>1 PW) lasers have been an object of intense research [1]. It is motivated by pushing the frontiers of the peak power. Another reason is increasing the temporal resolution in pump-probe experiments. The temporal contrast of these lasers is extremely high (>107) and preserving it after the pulse shortening is still a challenge. The common approach for femtosecond pulse shortening includes spectral broadening in a third order nonlinear medium and residual chirp compensation in a pulse compressor. An alternative approach is based on cascaded second order nonlinearities. Although both methods have been successfully demonstrated [2,3], there is no comparison of their capabilities to preserve the temporal contrast. In this report, we compare these two techniques: considering two criteria: the output pulse duration and the temporal contrast.