Abstract

The interaction of acoustic waves with charged colloids results in electrical signals. This phenomena, known as the Debye effect, results due to the instantaneous separation between the charged colloidal particle and its surrounding double layer. The separation results in a macroscopic polarization within the medium, which creates a voltage difference. This work demonstrates that radiation pressure forces can be used to impulsively move the colloid, resulting in a dipolar electric field. Experiments were performed using 100 ps, 1.06-µm pulses and 80 ps, 532-nm pulses incident on aqueous colloidal suspensions of charged latex spheres. Experiments were performed on random colloidal suspensions as well as high density crystals ordered in an fcc lattice. The dependence of the effect on sphere size and pulse intensity are presented. The effect exhibits the expected polarity when opposite sides of the sample are illuminated. Using electro-optic sampling, the dynamics of the double layer response can be directly probed on a picosecond time scale.

© 1990 Optical Society of America