ULTRASONIC MODULATION OF MULTIPLY SCATTERED-LIGHT

We report the first observation of ultrasonic modulation of multiple l ight scattering speckles. The modulation at integral(a) = 2 MHz of the temporal field autocorrelation function <E(0)E(t)> of the light scat tered from concentrated aqueous suspensions of polystyrene beads was m easured. In addition, when using integral(a) = 27 MHz, the light inten sity spectra measured with a Fabry-Perot interferometer show four inel astic peaks at integral(a) and 2 integral(a) from the principal Raylei gh peak. The modulation amplitudes obtained from both techniques were found to increase with the ultrasonic amplitude and to vary with the m ean free path of light in agreement with our simple model.