Laser ultrasonic micromanipulator

Abstract

Previously we have proposed ultrasonic micromanipulation (UMM) techniques for micron-sized particles in liquid based on the radiation forces of very-high-frequency (VHF) ultrasound. In this paper, we report a new laser ultrasonic micromanipulator (LUMM) in which the acoustic radiation force and optical radiation force combine complementarily as noncontact force. An experimental LUMM consists of an acoustic leaky wave transducer of center frequency 49 MHz, a laser diode with a maximum power 5 mW at 675 nm and a biological microscope. Using the LUMM, we have carried out successfully the rapid selection of a specific particle in liquid by the removal of unwanted particles from large number of 12-/spl mu/m-diameter polystyrene spheres. The LUMM was also used to estimate the horizontal component of the ultrasonic radiation force based on the Stokes law from the measured critical velocity at which the trapping is released by mechanically moving particles.