Laser induced grating

A laser-induced gratings (LIG, engl .: laser induced grating ) is an optical grating by interference of two laser beams is produced, which at a point of a nonlinear optical are focused material.

In the zones of constructive interference , these properties of the material change the optical material constants compared to the zones of destructive interference. As a result, an optical grating is generated for the duration of the irradiation , which, depending on the cause of this optical non-linearity, can be a phase grating or an absorption grating or a mixture of both. The cause of the change in the optical properties are either thermal or purely electronic excitations in the medium (solids, liquids or gases), which induce a local change in the absorption index or the refractive index of the irradiated areas compared to those of the destructive interference.

If the two interfering laser beams are intense enough, the diffracted orders of the laser beams generated on the induced grating can be recognized with the naked eye even without a detector. One speaks of self- diffraction when the laser beams bend on their own grid. If a third laser beam is bent on it, one speaks of extraneous diffraction .

The angle of incidence between the two incident rays and their wavelength determine the grating constant of the induced optical grating.

If the two incident beams of different wavelengths, it comes through the optical beat at current grids, the interference pattern then moves with the speed of the beat frequency as a so-called running grid across the sample.

These phenomena can be used in optical spectroscopy to study z. B. use diffusion lengths of electronic or thermal processes in gases and solids.

literature

• HJ Eichler , P. Günter, DW Pohl: Laser induced dynamic gratings. Springer, Berlin et al. 1986, ISBN 3-540-15875-8 ( Springer Series in Optical Sciences 50).