Hyper-Raman microspectroscopy: A new approach to completing vibrational spectral and imaging information under a microscope

We have developed hyper-Raman scattering microspectroscopy and applied it to a microcrystal of all-trans-β-carotene. The hyper-Raman spectrum of all-trans-β-carotene exhibits a Raman-inactive but infrared-active vibrational mode at 1564 cm^-1. Hyper-Raman imaging of a microcrystal was performed with this band. Infrared-active vibrational imaging was achieved with a spatial resolution much higher than that of conventional infrared microscopy. The combination of Raman and hyper-Raman spectroscopy opens up a new scope for high-spatial-resolution vibrational microspectroscopy that is not restricted by the selection rule.