Application of laser tweezers for material science studies

Abstract

Experimental results on laser tweezers technology application for material science researche performed at the Institute for Lasers, Photonics and Biophotonics, University at Buffalo, SUNY are presented. Computer controlled dual-beam laser tweezers for highly efficient trapping and manipulation of micron and sub-micron size objects was designed and built. A novel technique for the calibration of laser tweezers that utilize two-photon excited fluorescence of commercial dye stained microspheres has been demonstrated. Laser tweezers technology has been used to monitor the bulk solution viscosity during the sol-gel gelation process at different depths from an interface. The gelation rate is the same in depth ranges 2 - 20 microns from the bounding surface. Optical trapping and manipulation of transparent microparticles suspended in a thermotropic nematic liquid crystals with small and large birefringence was also demonstrated. We employ the particle manipulation to measure line tension of a topologically stable disclination line and to determine colloidal interaction of particles with perpendicular surface anchoring of the director. Fast scanning beam multiple trap option of laser tweezers to construct and dynamically control micro-array structures was developed and characterized. Main parameters of scanning multiple trap setups were studied and optimized. Combination of optical trapping with the hot fluorescence phenomena has been used for local temperature monitoring in liquid samples,with under micron size resolution.