Population and Thermal Grating Contributions to Degenerate Four-Wave Mixing Line Shapes

Degenerate four-wave mixing (DFWM) is a laser-induced grating technique that shows increasing potential as a diagnostic probe for reactive environments. Traditionally, the development of DFWM as a diagnostic for gaseous systems has focused on using the population-grating (PG) mechanism to measure concentration and temperature. Recently, several authors have observed a thermal-grating (TG) mechanism in gases. This mechanism is similar to that observed for many years in liquids and solids.1 The gas-phase thermal-grating mechanism deserves further study since it can complicate population-grating measurements, or can itself be useful for making quantitative measurements.