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The small angle scattering of light from a pulsed CO2 laser has been used to measure ion acoustic waves excited in a low density plasma. The laser is a hybrid laser consisting of a high pressure TEA discharge and a low pressure continuous discharge. The scattered light is detected by heterodyning, using laser light as the local oscillator. Two methods of providing the laser light local oscillator have been used. The dependence of the scattered light on the ion acoustic wavelength has been measured. The amplitude of the scattered light compared with the amplitude of the waves in the plasma indicates that the heterodyne mixing efficiency is better than 10 percent.