Microparticles including biological cells were trapped and manipulated using a continuous wave tweezer and a femtosecond laser tweezer. The difference of the optical trapping force between CW and femtosecond optical tweezers increased as the particle size decreased, possibly due to the self-focusing effect of the ultrashort pulses. Also, the white damage spots were generated near the focus during femtosecond optical trapping of biological cells even with extremely low average power. The instantaneous optical damage threshold was measured as a function of the trap depth as well. These results may help to optimize the optical trapping of biological cells using femtosecond lasers.
Using an acousto-optic beam deflector and a line scan camera, we constructed a non-mechanical, slit-scanning confocal microscope. It generates two-dimensional 512x512 images with speed of 60 frames/sec, which can be easily expanded, to 100 frames/sec. The measured axial and lateral resolutions of the system are 3.3 mm and <1 mm, respectively, with a 50X objective. This simple design can produce frames rates faster than other commercial products with comparable resolution, which may be useful for analysis of rapid interactions in various biological applications.
We trapped and manipulated the micro-particles by two beam interference. The micro-particles were pulled toward the bright fringe and were aligned along the periodic interference pattern. We observed the distribution of trapped particles at the various polarization configurations by adjusting the polarization states and measured the optical force acting on the particles. The particles were trapped in bright fringe by intensity gradient in the case of parallel polarization state. In the case of perpendicular polarization state, the particles aligned along periodic pattern even though there was no intensity modulation. Consequently, the results showed that the optical force can be generated from not only the intensity modulation but also no intensity modulation.