  Using the shifted-excitation Raman difference spectroscopy technique and an
optical fibre featuring a negative curvature excitation core and a coaxial ring
of high numerical aperture collection cores, we have developed a portable,
background and fluorescence free, endoscopic Raman probe. The probe consists of
a single fibre with a diameter of less than 0.25 mm packaged in a
sub-millimetre tubing, making it compatible with standard bronchoscopes. The
Raman excitation light in the fibre is guided in air and therefore interacts
little with silica, enabling an almost background free transmission of the
excitation light. In addition, we used the shifted-excitation Raman difference
spectroscopy technique and a tunable 785 nm laser to separate the fluorescence
and the Raman spectrum from highly fluorescent samples, demonstrating the
suitability of the probe for biomedical applications. Using this probe we also
acquired fluorescence free human lung tissue data.
