Brownian Motion in an Optical Trap (Low NA) — Geometrical Optics

This video shows a spherical particle (glass, refractive index: np = 1.50) in water (nm = 1.33) subject to Brownian motion and to the optical force produced by a Gaussian beam focused by an objective with low numerical aperture (NA= 0.5). In order to be able to see the effect of Brownian motion, the power of the beam was set equal to 0.1mW. The black arrow shown indicates the direction of the optical force on the particle (propely rescaled).

Agnese Callegari, Mite Mijalkov, A. Burak Gököz, and Giovanni Volpe, “Computational toolbox for optical tweezers in geometrical optics,” J. Opt. Soc. Am. B 32, B11-B19 (2015).