In-situ background-free Raman endoscope using double-cladding anti-resonant hollow-core fibers

This paper presents the development of an in-situ background-free Raman fiber endoscope, employing two customized double-cladding anti-resonant hollow-core fibers (AR-HCFs). The Raman background noise measured in the AR-HCF probe is lower than that of a conventional multi-mode silica fiber by two orders of magnitude. A plug-in device of fiber coupling optics is designed that is compatible with the commercially available confocal Raman microscope, enabling in-situ Raman detection. The numerical aperture (NA) of both AR-HCF claddings exceeds 0.2 which substantially enhances the collection efficiency of Raman signals at the distal end of the fiber probe. The performance of our Raman fiber endoscope is demonstrated by characterizing samples of acrylonitrile–butadiene–styrene (ABS) plastics, alumina ceramics, and ethylene glycol solution.