Axial position detection for optical tweezers based on Moiré Deflectometry

Optical tweezers are indispensable instruments for applying and measuring Pico-Newton range forces. The magnitude of the exerted force is determined by measuring the displacement of the trapped bead from the center of the trap. Recently, we developed a new detection system for optical tweezers based on Moiré Deflectometry (MD). In this work, we show, both theoretically and experimentally, that the introduced method can be used for detection in the axial direction, as well, with a significantly larger sensitivity compared to the commonly used QPD method. As an example, for a 2.17μm polystyrene bead this method could provide a sensitivity 285% larger than that of the QPD method.