Sensitivity of displacement detection for a particle levitated in the doughnut beam.

Displacement detection of a spherical particle in focused laser beams with a quadrant photodetector provides a fast and high precision way to determine the particle location. In contrast to the traditional Gaussian beams, the sensitivity of displacement detection using various doughnut beams is investigated. The sensitivity improvement for large spherical particles along the longitudinal direction is reported. With appropriate vortex charge l of the doughnut beams, they can outperform the Gaussian beam to get more than one order of magnitude higher sensitivity and, thus, have potential applications in various high-precision measurements. By using the levitating doughnut beam to detect the particle displacement, the result will also facilitate the recent proposal of levitating a particle in doughnut beams to suppress the light absorption.