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

The nature of optical scattering from laser-induced thermal gratings created in the gas phase is investigated. Thermal gratings are produced with the illumination geometry used to perform degenerate four-wave mixing (DFWM) measurements. Such scattering from thermal gratings can act as a phase-matched interference signal. A solution to the linearized hydrodynamic equations is developed to model the dynamics of the thermal grating. Predictions of this model that uses realistic gas properties are shown to compare favorably with laboratory measurements. The model includes the effects of finite-rate energy deposition, damping by viscosity and thermal conduction, mass diffusion of the excited-state grating, and electrostrictive compression.