Influence of Kerr Anisotropy in Parametric Amplification

Four-wave parametric amplification can be extended to the TW/cm$^2$ regime using femtosecond pump pulses to amplify nearly octave spanning pulses with gain $> 20$~mm$^{-1}$, which we call Kerr instability amplification. Cross-polarized wave generation exploits Kerr anisotropy to induce a transient intensity-dependent polarization evolution. In this work, we combine Kerr instability amplification with cross-polarized wave generation to simultaneously amplify and rotate the output polarization of a signal beam, and we explore laser and crystal parameters to control the resulting polarization. In 1~mm MgO(100), we amplify linearly polarized light by $2000\times$ orthogonal to the pump and seed polarization. The parametric amplification and polarization rotation offers excellent pulse contrast enhancement for future high-power laser systems. Furthermore, the polarization provides an additional observable to study the nonlinear dynamics occuring in this extreme ultrafast light-matter interaction.