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Sagnac interferometer-enhanced particle tracking in optical tweezers




Taylor, Michael A
Knittel, Joachim
Hsu, Magnus
Bachor, Hans
Bowen, Warwick

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Institute of Physics Publishing


A set-up is proposed to enhance tracking of very small particles, by using optical tweezers embedded within a Sagnac interferometer. The achievable signal-to-noise ratio is shown to be enhanced over that for standard back-focal-plane interferometry. The enhancement factor increases asymptotically as the interferometer visibility approaches 100%, but is capped at a maximum given by four times the ratio of the trapping field intensity to the detector saturation threshold. For an achievable visibility of 95%, the signal-to-noise ratio can be enhanced by a factor of up to 158 and the minimum trackable particle size is 2.3 times smaller than without the interferometer. This technique is particularly useful for optical tweezers which require counter-propagating trap beams.



Keywords: Back focal planes; Counterpropagating; Enhancement factor; particle tracking; Sagnac interferometer; Signal to noise; Small particles; Trapping fields; Fiber optic sensors; Interferometers; Shot noise; Signal to noise ratio; Visibility; Optical tweezers optical tweezers; particle tracking; Sagnac interferometer; shot noise limited sensing



Journal of Optics


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