Directed rotational motion of birefringent particles by randomly changing the barrier height at the threshold in a washboard potential

Basudev Roy, Erik Schaffer

This communication presents a simulation study of the directed rotational motion of a birefringent spherical particle trapped in optical tweezers with randomly varying ellipticity of a trapping light at the point of threshold. When noise is not applied, the potential barrier due to the linear component of the polarization is simulated to be sufficient to prevent directed rotation till a certain threshold value of ellipticity. Random variations to the ellipticity cause random variations in the barrier height, including instants when the barrier is lower than the threshold energy level. It is due to this that the particle exhibits directed rotational motion at ellipticity lower than the threshold value. We also examine the rotational velocity of the birefringent particle as a function of the extent of zero-mean random noise applied to the ellipticity.

DOI

Two-photon fluorescence diagnostics of femtosecond laser tweezers

Arijit Kumar De, Debjit Roy and Debabrata Goswami

We show how two-photon fluorescence signal can be used as an effective detection scheme for trapping particles of any size in comparison to methods using back-scattered light. Development of such a diagnostic scheme allows us a direct observation of trapping a single nanoparticle, which shows new directions to spectroscopy at the single-molecule level in solution.

DOI