GAS-PHASE THERMAL-GRATING CONTRIBUTIONS TO 4-WAVE-MIXING

The nature of optical scattering from laser-induced thermal gratings c reated in the gas phase is investigated. Thermal gratings are produced with the illumination geometry used to perform degenerate four-wave m ixing (DFWM) measurements. Such scattering from thermal gratings can a ct as a phase-matched interference signal. A solution to the linearize d hydrodynamic equations is developed to model the dynamics of the the rmal grating. Predictions of this model that uses realistic gas proper ties are shown to compare favorably with laboratory measurements. The model includes the effects of finite-rate energy deposition, damping b y viscosity and thermal conduction, mass diffusion of the excited-stat e grating, and electrostrictive compression.