Raman imaging through multimode sapphire fiber.

Sunan Deng,Demetri Psaltis,Christophe Moser,Damien Loterie,Georgia Konstantinou

doi:10.1364/oe.27.001090

Abstract

We report on a sapphire fiber Raman imaging probe's use for challenging applications where access is severely restricted. Small-dimension Raman probes have been developed previously for various clinical applications because they show great capability for diagnosing disease states in bodily fluids, cells, and tissues. However, applications of these sub-millimeter diameter Raman probes were constrained by two factors: first, it is difficult to incorporate filters and focusing optics at such small scale; second, the weak Raman signal is often obscured by strong background noise from the fiber probe material, especially the most commonly used silica, which has a strong broad background noise in low wavenumbers (<500-1700 cm-1). Here, we demonstrate the thinnest-known imaging Raman probe with a 60 μm diameter Sapphire multimode fiber in which both excitation and signal collection pass through. This probe takes advantage of the low fluorescence and narrow Raman peaks of Sapphire, its inherent high temperature and corrosion resistance, and large numerical aperture (NA). Raman images of Polystyrene beads, carbon nanotubes, and CaSO4 agglomerations are obtained with a spatial resolution of 1 μm and a field of view of 30 μm. Our imaging results show that single polystyrene bead (~15 µm diameter) can be differentiated from a mixture with CaSO4 agglomerations, which has a close Raman shift.

Highlights

Raman spectroscopy is a powerful analytical tool to detect the frequency shift in the inelastic light scattering due to the molecular vibrational modes in a sample [1,2]
Small dimension Raman probes have been developed for various clinical applications as they show great potential for diagnosing disease states in bodily fluids, cells, and tissues [11]
We demonstrate the capability of our approach for a Raman imaging probe by imaging and detecting polystyrene beads, carbon nanotube (CNT) paper, and CaSO4 agglomerations

Summary

Introduction

Raman spectroscopy is a powerful analytical tool to detect the frequency shift in the inelastic light scattering due to the molecular vibrational modes in a sample [1,2]. Small scale probes enable new applications, either adapting to endoscopy [15] or working as needle probe [16], their optical design are constrained by the difficulty of incorporating filters and lenses at this scale. Another challenge in the development of small Raman probes is the weak signal from the sample that is often obscured by fluorescence and Raman background from the probe material [17]. We propose and demonstrate a very thin Raman imaging probe based on a 60 μm diameter multimode sapphire optical fiber (air cladding) for both the excitation and collection of Raman signal, without any additional focusing optics. Our results show that single polystyrene bead (~15 μm diameter) can be differentiated from a mixture with CaSO4 agglomerations, which has a close Raman shift

Experimental setup

Summary and conclusions