Accurate centroid position measurements of a light spot are vital for optical tweezers. To get quantitative measurements we can find the optical force by measuring the change in momentum of the trapping beam and track the position of the trapped particle using its image. We propose to use a filter with a linear transmittance to modulate the amplitude of the input beam in such a way that the transmitted intensity of the light will be proportional to the displacement of the spot. Our method is compared with existing methods and we find that it provides accurate measurements at high bandwidth.
Anatolii V. Kashchuk, Alexander B. Stilgoe, Timo A. Nieminen, and Halina H. Rubinsztein-Dunlop, "High-speed position and force measurements in optical tweezers (Conference Presentation)," Proc. SPIE 10347, Optical Trapping and Optical Micromanipulation XIV, 1034717 (Presented at SPIE Nanoscience + Engineering: August 07, 2017; Published: 25 September 2017); https://doi.org/10.1117/12.2274673.5588446489001.
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