Acoustic wave calibration for CO2 laser scattering experiments

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Abstract
An acoustic wave technique is described which provides an absolute calibration of the amplitude of the light scattered from a CO2 laser beam at near‐forward angles by fluctuations in plasmas or other media. This technique also provides a direct measure of the wavelengths of fluctuations that can be resolved by CO2 laser light scattering. Using simple vibrating membranes, acoustic waves with wavelengths from a few millimeters to several centimeters can be generated with accurately measured amplitudes. Laser scattering from these waves verifies that wavelengths as long as 2 cm can be resolved with small‐angle CO2 laser scattering. For the case of heterodyne detection, calibration of the scattered wave amplitudes is obtained to within ± 20%.