Raman imaging through multimode sapphire fiber

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 CaSO 4 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 CaSO 4 agglomerations, which has a close Raman shift.

Observing distant objects with a multimode fibre-based holographic endoscope

“…The far-field modality can thus be used to guide the insertion of the probe while providing organ-or tissue-scale imagery, which can then be promptly converted into an instrument imaging at the subcellular scale. Combined with spectroscopic imaging methods [30][31][32], the technology has potential for in situ diagnostics at the cellular level.…”

Fabrication and Application of Single Crystal Fiber: Review and Prospective

“…In Section 5.5, we have shown that sapphire has much weaker and narrower Raman peaks. Such Raman background with high transparency provides a clean spectrum and high imaging quality, [ 194 ] with the system illustrated in Figure . A sapphire fiber (Micromaterials, Inc. 5 cm long with 60 µm core) is used to deliver the excitation laser and collect the Raman scattering from the sample simultaneously.…”

A Miniature Fibre-Optic Raman Probe Fabricated by Ultrafast Laser-Assisted Etching

“…However, the fibre material itself, commonly silica, produces a Raman signal as the pump light propagates along it (referred to as the fibre background, FB) which can be several orders of magnitude greater than the tissue Raman signal. Recent advances in fibre manufacturing have opened up new avenues to address this; notably, non-standard fibre materials such as sapphire [28] and microstructured, hollow-core fibres [29,30] have been shown to dramatically reduce the fibre background signal. Single-fibre probes still exhibit limited collection efficiency and so instead multicore fibres or fibre bundles are sometimes used to improve signal collection without increasing the complexity of manufacture significantly [31,32].…”