Raman imaging through multimode sapphire fiber.

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 mu m 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 CaSO(4 )agglomerations are obtained with a spatial resolution of 1 tun and a field of view of 30 mu m. Our imaging results show that single polystyrene bead (similar to 15 mu m diameter) can be differentiated from a mixture with CaSO(4 )agglomerations. which has a close Raman shift. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement