Optical lock-in particle tracking in optical tweezers

We demonstrate a lock-in particle tracking scheme in optical tweezers based on stroboscopic modulation of an illuminating optical field. This scheme is found to evade low frequency noise sources while otherwise producing an equivalent position measurement to continuous measurement. This was demonstrated to yield up to 20 dB of noise suppression at both low frequencies (< 1 kHz), where low frequency electronic noise was significant, and around 630 kHz where laser relaxation oscillations introduced laser noise. The setup is simple, and compatible with any trapping optics.