Nonlinear Mie scattering: electrostrictive coupling of light to droplet acoustic modes

Nonlinear Mie scattering at 532 nm was observed from 23-microm-diameter ethanol droplets excited by picosecond light pulses. Low-order optical modes (l = 2-4), normally hidden at low intensity, became visible as new peaks in elastic scattering spectra at 2 GW/cm(2). When higher-Q resonances were selectively excited, the scattered light showed an amplitude-modulated time dependence. The data are explained by electrostrictive generation of acoustic modes of the droplet by the incident radiation and subsequent coupling of the acoustic disturbance back onto the light field.