DEVELOPMENT OF THE LASER ULTRASONIC MICROMANIPULATOR

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Noncontact and nondestructive techniques for manipulation, such as transportation, trapping, and separation of micron-sized particles in liquid, are currently of considerable interest in areas of biotechology and micromachining. Optical tweezers are a known example of noncontact manipulation of small particles. Radiation pressure from laser beams is used. However, trapping is difficult for particles that have a small refractive index or are metallic. Also, the narrow width of optical potential wells is a significant limitation for the continuous manipulation of the small particles. 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. Using the visual feedback technique we demonstrated two-dimensional manipulation of a polystyrene sphere along a circle and character patterns.In this study, we have developed a new laser ultrasonic micromanipulator (LUMM) in which the acoustic radiation force and optical radiation force are both used as complementary noncontact forces. All experimental LUMM consists of an acoustic leaky wave transducer of center frequency 49 MHz, a Baser 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-μm-diameter polystyrene spheres.The LUMM was also used to estimate the horizontal component of the ultrasonic radiation force by using Stokes law and the measured critical velocity at which the trapping is released by mechanically moving particles. Parts of these results are presented in IEEE 2000 Ultrasonics Symposium. The unpublished results will be presented in near future.