  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, and found to yield on average 20dB of noise suppression in the
frequency range 10-5000 Hz, where low frequency laser noise and electronic
noise was significant, and 35 dB of noise suppression in the range 550-710 kHz
where laser relaxation oscillations introduced laser noise. The setup is
simple, and compatible with any trapping optics.
