Controlling laser beams with Brillouin and photorefractive nonlinearities

Controlling the properties and the quality of the beams emitted by CW or pulsed lasers is now becoming of great interest for high performance laser systems. Such objectives involve the coherent beam interference of pump and probe beams in materials which exhibit a photoinduced change of their refractive index. Due to energy transfer of the pump beam, a low intensity wavefront can be either efficiently amplified or phase conjugated with a high reflectivity (two wave and four wave mixing configurations). For these purposes, it is now well recognized that the stimulated Brillouin scattering (SBS) and the photorefractive effects (PRE) have very attractive capabilities. The first part of the lecture, will review the basic properties of the mentioned above nonlinearities and will identify the field of application of the different mechanisms according to the laser characteristics such as: operating wavelength, pulse duration, repetition rate and input fluence. In particular, it will be outlined that the PRE is particularly adapted to CW visible or near IR lasers while SBS is mostly convenient for Q-switched IR sources. We develop in the following two original applications which involve the SBS and the PRE, respectively for a 30 Hz phase conjugate Nd:YAG laser with beam steering and, for low noise and high gain photorefractive image amplification and detection