Frequency response of a thermally driven atmosphere.

A focus dithered CO(2) beam has been used to thermally dither the atmosphere in a laboratory thermal blooming cell. The amplitude and phase response of the dithered atmosphere were measured using both an He-Ne laser and a CO(2) laser. If a relaxation time determined by the beam diameter and the crosswind velocity is introduced, the atmospheric response can be described analytically by using the theory for the propagation of acoustic waves in an absorptive and dispersive fluid.