Laser-induced thermal grating effects in flames.

Light scattering from a laser-induced thermal grating produced in an atmospheric-pressure H(2)/O(2) flame is observed with a phase-matching geometry commonly used in resonant four-wave mixing and laser-induced grating spectroscopy. The presence of thermal gratings is confirmed in both the time and the frequency domains in two distinct experiments. Diluting the flame with helium decreases the thermal grating signal intensity. Experimental results agree well with calculations based on a solution of the linearized hydrodynamic equations.