Efficiency enhancement of Raman microspectroscopy at long working distance by parabolic reflector

Raman microspectroscopy is well suited for readily revealing information about bio-samples. As such, this technique has been applied to a wide range of areas, especially in bio-medical diagnosis. However, bio-samples typically suffer from low Raman signal level due to the nature of inelastic scattering of photons, To achieve a decent signal level, usually a high numerical aperture is employed. One drawback with these objectives is that their working distance is very short. In many cases of clinic diagnosis, a long working distance is always desired which limits the usage of these objectives. We propose a practical solution to this problem by enhancing the Raman/fluorescence signal by a parabolic reflector. On one hand, the high signal level is achieved by the large solid angle of collection of the parabolic reflector. On the other hand, the long working distance is guaranteed by the novel design of our microscope. The enhancement-capability is demonstrated through five types of samples among which we found the method is most applicable for turbid samples.