The Brownian dynamics of an optically trapped water droplet is investigated across the transition from over to under-damped oscillations. The spectrum of position fluctuations evolves from a Lorentzian shape typical of overdamped systems (beads in liquid solvents), to a damped harmonic oscillator spectrum showing a resonance peak. In this later under-damped regime, we excite parametric resonance by periodically modulating the trapping power at twice the resonant frequency. We also derive from Langevin dynamics an explicit numerical recipe for the fast computation of the power spectra of a Brownian parametric oscillator. The obtained numerical predictions are in excellent agreement with the experimental data.

Date Published: 5 September 2007
PDF: 9 pages
Proc. SPIE 6644, Optical Trapping and Optical Micromanipulation IV, 66441J (5 September 2007); doi: 10.1117/12.736448

Published in SPIE Proceedings Vol. 6644:
Optical Trapping and Optical Micromanipulation IV
Kishan Dholakia; Gabriel C. Spalding, Editor(s)