We demonstrate the simultaneous measurement of optical trap stiffness and quadrant-cell photodetector (QPD) calibration of optically trapped polystyrene particle in air. The analysis is based on the transient response of particles, confined to an optical trap, subject to a pulsed electrostatic field generated by parallel indium tin oxide (ITO) coated substrates. The resonant natural frequency and damping were directly estimated by fitting the analytical solution of the transient response of an underdamped harmonic oscillator to the measured particle displacement from its equilibrium position. Because, the particle size was estimated independently with video microscopy, this approach allowed us to measure the optical force without ignoring the effects of inertia and temperature changes from absorption.
Haesung Park and Thomas W. LeBrun, "Forces and dynamics of optically levitated polystyrene particles in air using electrostatic modulation," Proc. SPIE 9548, Optical Trapping and Optical Micromanipulation XII, 95480E (Presented at SPIE Nanoscience + Engineering: August 09, 2015; Published: 25 August 2015); https://doi.org/10.1117/12.2191546.
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