Determining size of an optically trapped particle via modulated Raman spectroscopy

TL;DR

This paper presents a method to determine the size of optically trapped particles by analyzing the modulation-dependent Raman signal, linking hydrodynamic properties to optical measurements.

Contribution

It introduces a novel approach using modulated Raman spectroscopy and Langevin dynamics to estimate particle size in optical trapping.

Findings

Multiple minima in Raman signal at specific modulation frequencies.

Minima can reduce Raman signal to as low as 50%.

Method enables size estimation from Raman signal variations.

Abstract

The average Raman signal power obtained in a modulated optical trap is dependent on the Brownian motion - therefore hydrodynamic properties of the trapped particle. Hence, in addition to the molecular properties obtained from the Raman signal, it is possible to study hydrodynamic properties (e.g. size) of the particle by analyzing the change in the average Raman power as a function of modulation frequency. Our results, based on the over-damped Langevin equation, show that several minimas exist for the Raman signal at unique modulating frequencies for a given particle size and signal acquisition time. In typical experimental conditions, such minimas can be as low as 50% of the Raman signal in an unmodulated trap.