Optical heterodyne detected transient grating for studies of photochemical reactions and solution dynamics

An optical heterodyne detected transient grating (TG) setup was constructed by a slight modification of a conventional TG setup without an active feedback system for studying photophysical and photochemical processes from nanoseconds to seconds time range. The linearized signal significantly enhances the sensitivity of a weak signal and this capability was used for studying the diffusion process of trans- and cis-isomers of Methyl red. We found that the thermal lens contribution was inevitable to the signal and had to be eliminated.