Sub-millimetre flexible fibre probe for background and fluorescence free Raman spectroscopy

We have developed a compact background and fluorescence free endoscopic Raman probe using shifted-excitation Raman difference spectroscopy (SERDS) with an optical fibre featuring a negative curvature excitation core and a coaxial ring of multimode collection cores. The probe consists of a single optical fibre with an outer diameter below 0.25 mm packaged in sub-millimetre tubing making it compatible with the working channels of standard endoscopic tools. The light in the fibre is guided in air and therefore interacts little with silica, enabling an almost background-free transmission of the excitation light and collection using a single optical fibre. In addition, we used the SERDS technique and a tunable 785 nm laser to separate the fluorescence and the Raman spectrum from highly fluorescence samples, demonstrating the suitability of the probe for biomedical applications.