Revolution of a trapped particle in counter-propagating dual-beam optical tweezers under low pressure

Abstract

We presented faster and more accurate simulations and experiments describing the revolution of a suspended particle in optical tweezers under a low pressure. Instead of the state-of-the-art offline method of pinhole alignment, we proposed an in situ method of revolution suppression by adjusting the laser beam while observing the power spectral density and time-domain plot of the particle centroid displacement. The experimental results under different air pressures show that our method is more effective at low pressures. We observed that “revolution occurs when radial alignment error is below the threshold” and uncovered the mechanism behind this phenomenon. The rapidly growing Q value of the revolution indicates a high-precision resonance measurement method under lower air pressure compared with random translation measurements.

Orbital Dynamics at Atmospheric Pressure in a Lensed, Dual-beam, Optical Trap

“…Under our experimental conditions, the power spectral distribution of particle's motion exhibits sharp peaks with narrow widths, at least two orders of magnitude narrower than those associated with periodic oscillation of a trapped particle in air. The apparent quality factors are also considerably higher than what has been reported for trapping with fiber optic traps in low vacuum 22 . Since high mechanical Q factors are desirable for accurate determination of change in the resonance frequency upon particle size and/or mass change 23,24 , our results have significant implications for the use of optical trapping to probe the kinetics of surface reactions on levitated particles at atmospheric pressure.…”

“…For instance one can allow in the medium for random, Langevin forces in addition to viscous drag 21,22 . One also can do a full 3D calculation of forces, including forces and motion in the the y-direction 21,22 .…”

“…For instance one can allow in the medium for random, Langevin forces in addition to viscous drag 21,22 . One also can do a full 3D calculation of forces, including forces and motion in the the y-direction 21,22 . We have done a few 3D calculations but find that the motion in the xz plane is scarcely changed, with the excursions along y being a small fraction of a micron.…”

“…Subsequently, orbital motion of dielectric micro-particles was achieved in both air 21 and low vacuum 22 , with counter-propagating, dual-beam offset fiber optic traps. While convenient, fiber optic based traps have physical limitations related to geometric constraints, which limit spatial control.…”

Analysis and Suppression of Laser Intensity Fluctuation in a Dual-Beam Optical Levitation System

“…A 5 µm pinhole and piezo inertia actuators (8301NF, Newport Inc., Irvine, CA, USA) with a minimum step size of dm = 30 nm are used to align the beams. It is ensured that the two beams are focused on the same point [ 22 ]. The levitated particle is an SiO 2 sphere that is 3 µm in diameter.…”