Bessel-beam illumination Raman microscopy.

We demonstrate the use of Bessel beams for side illumination slit-scanning Raman imaging for label-free and hyperspectral analysis of cell spheroids. The background elimination by the side illumination and the aberration-resistant Bessel beam drastically improves the image contrast in Raman observation, allowing label-free investigation of intracellular molecules in thick biological samples. Live cell spheroids were observed to confirm the improvement in image contrast and background reduction with Bessel illumination compared to conventional epi-line illumination.