Optically pumped and matrix‐assisted anti‐Stokes Raman spectroscopy

Abstract

AbstractAnti‐Stokes Raman spectroscopy is an excellent method to suppress optical backgrounds from Raman scatters and surrounding materials, even in electronic resonance conditions. The upshift of scattered light can avoid the fluorescence or phosphorescence that is usually red‐shifted with respect to the excitation wavelength. However, this method's competence is circumscribed by its low scattering efficiency, which results from an insufficient population of upper vibrational states that obey temperature‐dependent Boltzmann statistics. To overcome this limitation, we propose that the mode‐selective absorption of overtone or combination vibrations leads to enhanced anti‐Stokes Raman scattering under simultaneous optical pumping and Raman excitation. In this work, we applied near‐infrared (NIR) pumping resonant with vibrational overtones of nonfluorescent systems. Vibrationally resonant pumping is efficient for population transfer, and the excess energy is thermodynamically distributed over all fundamental vibrations. Furthermore, we present that NIR absorbing molecules can be employed as matrices to amplify anti‐Stokes Raman signals of weak scattering targets.