Theory of groove-envelope phase effects in self-diffraction

TL;DR

This paper develops models to understand how the phase between laser-induced grating grooves and their envelope influences self-diffraction patterns, especially under conditions with few grooves and high intensities.

Contribution

It introduces new models for groove-envelope phase effects in self-diffraction, including a beyond-four-wave-mixing approach for high-intensity regimes.

Findings

Four-wave mixing causes dominant interferences between diffraction orders.

Vertical interference fringes near damage threshold require a new model.

Models successfully reproduce observed interference patterns.

Abstract

If two laser beams cross in a medium under shallow angle, the laser-induced grating consists of only a few grooves. In this situation, the phase between the grooves of the grating and its envelope is a decisive parameter for nonlinear effects. Here, models are established for reproducing the groove-envelope phase effects that have been observed in the interference pattern of self-diffraction. Four-wave mixing leads to interferences that are dominant in the spatial region between the orders of diffraction and with tilted interference fringes in the diagram of transverse coordinate vs. pulse delay. The vertical interference fringes that are dominant directly on the diffraction orders, experimentally observed at high intensity close to the damage threshold, require a model beyond four-wave mixing. A model is suggested that is based on optical transmission changes with confinement to regions in the medium that are smaller than the groove spacing.