Thermal broadening of the power spectra of laser-trapped particles in vacuum

TL;DR

This paper demonstrates that at low pressures, the spectral widths of laser-trapped particles are primarily determined by thermal distributions and trap nonlinearities, revealing insights into particle temperature and trap characteristics.

Contribution

The authors develop a theoretical model linking spectral widths to thermal energy and trap depth, explaining experimental observations for nanoparticles and extending to smaller particles.

Findings

Spectral widths are pressure-independent at low pressures.

Widths are broader along the optical lattice direction.

Larger nanoparticles exhibit narrower spectral widths.

Abstract

We show that at low pressures the spectral widths of the power spectra of laser-trapped particles are nearly independent from pressures and, due to the nonlinearities of the trap, reflect the thermal distribution of particles. In the experiments with nanoparticles trapped in an optical lattice, we identify two distinct features of the widths. First, the widths along an optical lattice are much broader than those in the other directions. Second, the spectral widths are narrower for larger nanoparticles. We develop a theory of thermal broadening and show that the spectral widths normalized by the frequencies of the center-of-mass motion directly reveal the ratio of the thermal energy to the trap depth. The presented model provides a good understanding of the observed features. Our model holds also for smaller particles such as atoms and molecules and can be readily extended to the general case with a single-beam optical trap.