The interference pattern of two laser beams induces periodical variations of the optical properties of matter (refractive index and absorption coefficient). Induced grating structures have been observed in absorbing liquids and solids, plasmas, laser materials, dye solutions and semiconductors. These gratings have been applied to thermal diffusion measurements, excitation of high frequency normal and second sound waves, determination of electronic lifetimes, distributed feedback lasers and real-time holography. The literature on transient grating materials and applications is surveyed.

Laser-induced Grating Phenomena

The optical properties (refractive index and coefficient of absorption) of matter become spatially modulated in the interference region of two intensive light waves. The resulting grating patterns have been observed in liquids and solids by diffraction (“forced light scattering”) of a probing beam or by self-diffraction. Thereby the spatial amplitude of the optical constants is measured with interferometric sensitivity. Permanent gratings by been investigated extensively for holographic applications. This paper emphazises transient gratings, methods for measurement of fast grating decay times, and excitation mechanisms. Thermal gratings, corresponding to a spatially periodic temperature distribution, have been applied for temperature diffusivity measurements and excitation of different types of sound waves. In semiconductors gratings have been produced corresponding to a spatial modulation of the free carrier or exciton density.

Forced light scattering at laser-induced gratings—A method for investigation of optically excited solids

The three-wave interaction in nonlinear optics

Phase conjugation CS2 with 1% reflectivity by using a pulsed transversely excited atmospheric is CO2 laser Interesting pulse-reshaping effects, including acoustic modulation, are observed, and a thermal mechanism for the interaction is proposed

Phase conjugation in liquid CS2 by using a pulsed CO2 laser.

The application of the inverse scattering transform method (ISTM), a relatively new and potentially powerful analytic tool, to the three-wave interaction problem in nonlinear optics is reviewed. The method is particularly useful for the theoretical study of laser-induced dynamic gratings. As an illustrative example, the case of the electrostrictively induced sound wave is outlined in some detail. Other examples of the three-wave interaction, including those yielding soliton solutions, are also discussed. An extensive list of references to theory, experiment, and possible and actual applications is given.

H. Eiclhler

Papers

Thermal excitation of ultrasonnic waves by laser light