Distinguishing chemically similar particles in a complex environment via modulated field spectrometry

Abstract

Distinguishing chemically similar particles in a complex environment has been a challenging problem in spectroscopy, such as micro-Raman spectroscopy. Here, we show that it is possible to distinguish particles from their spectroscopic signals in a modulated optical trap, where the trapping field also acts as an excitation source. Using the overdamped Langevin equation, we report that spectroscopic signals averaged over a certain signal acquisition time exhibit several discrete minimas at unique modulating frequencies dependent on their drag coefficient, exemplified herein as a function of the particle size. In typical experimental conditions, such minimas can be as low as ∼50% of the signal of an unmodulated trap.