forced Rayleigh scattering spectroscopy thermal diffusion forced Rayleigh scattering S-FRSM A method for determining structure where a grating created by the interference of two laser beams is written into a sample which contains a small amount of dye. The intensity grating is converted into a temperature grating which, in turn, causes a concentration grating by thermal diffusion. A further laser beam is Rayleigh scattered by the grating and the change in direction or energy of the light and the temporal evolution of the scattered beam are measured. TDFRS thermal diffusion forced Rayleigh scattering thermal-diffusion forced Rayleigh scattering CHMO:0000177 SFRS TDFRS analysis TDFRS method SFRSM S-FRS Soret forced Rayleigh scattering method