Simultaneous nonlinear spectral broadening and temporal contrast enhancement of ultrashort pulses in a multi-pass cell

We study both numerically and experimentally the use of two third-order nonlinear temporal filtering techniques, namely nonlinear ellipse rotation and cross-polarized wave generation, for simultaneous nonlinear spectral broadening and temporal contrast enhancement of mJ energy, 30 fs titanium:sapphire laser pulses in a multi-pass cell. In both cases, a contrast enhancement greater than 3 orders of magnitude is observed, together with record high conversion efficiencies. Careful balancing of nonlinearity and dispersion inside the multi-pass cell helps tune the spectral broadening process and control the post-compressed pulse duration for specific applications.