All-optical amplification using unbalanced type II phase-matched second harmonic generation

We present increasing values of the input intensity, of the output polarisation direction for different ratio of the fundamental field input components on the SHG crystal axes. The data are given for a KTiOPO₄ crystal of 7 mm length and a fundamental wavelength of 1064 nm. The output polarization state corresponding to the linear propagation regime is preserved at high intensity and was kept linear here, but the output field undergoes a rotation of its polarization direction. The higher the difference in the o- and e components the stronger is the rotation effect at low intensity level. We propose and experimentally demonstrate that this effect can be used to achieve all-optical amplification