We describe the use of resonant amplification of light propelling forces for selective separation of fluid-suspended dielectric microparticles. The force amplification and the selectivity of the method is achieved using the whispering gallery mode resonances of the microparticles. The selectivity is determined by the inverse of the quality factor (Q) of the resonances in liquid (with Q ~ 104-106). We demonstrate that the evanescent field around a tapered optical fiber fed with ~20 mW power from a 1064 nm laser can selectively move polystyrene microspheres of up to 20 μm in diameter through distances of more than 50 μm, thereby establishing that the technique is sufficient for efficient separation.
Optical techniques are finding more and more use in the domain of nanoelectromechanical systems (NEMS). In particular, Michelson interferometry and Fabry-Perot interferometry have been employed to transduce high frequency motion of NEMS resonators. Here, we review our recent accomplishments in optical probing of NEMS. We discuss
the effectiveness of the above-mentioned optical techniques as the relevant NEMS dimensions are reduced beyond the optical probing wavelength.