Optical design for laser tweezers Raman spectroscopy setups for increased sensitivity and flexible spatial detection

Abstract

We demonstrate a method to double the collection efficiency in laser tweezers Raman spectroscopy (LTRS) by collecting both the forward-scattered and backscattered light in a single-shot multitrack measurement. Our method can collect signals at different sample volumes, granting both the pinpoint spatial selectivity of confocal Raman spectroscopy and the bulk sensitivity of non-confocal Raman spectroscopy simultaneously. Further, we display that our approach allows for reduced detector integration time and laser power. To show this, we measure the Raman spectra of both polystyrene beads and bacterial spores. For spores, we can trap them at 2.5 mW laser power and acquire a high signal-to-noise ratio power spectrum of the calcium-dipicolinic acid peaks using an integration time of ${2} \times {30}\;{\rm s}$. Thus, our method will enable the monitoring of biological samples sensitive to high intensities for longer times. Additionally, we demonstrate that by a simple modification, we can add polarization sensitivity and retrieve extra biochemical information.