Adaptive shaping and filtering of laser beams using photorefractive elements

Summary form only given. Two interfering beams inside a photorefractive crystal record a dynamic index grating. For a single mode laser, diffraction of the recording beams onto the induced grating leads to the well known two beam coupling phenomenon: energy is transferred from one beam to the other one. If the laser runs on several longitudinal modes, the energy exchange differs from mode to mode. The photorefractive crystal thus acts as a frequency filter whose spectral transmission depends on the spectral modal structure. We describe the main characteristics of several photorefractive self-adaptive filters based on either two or four wave mixings. We also show how such filters can modify the laser transverse structure.