Electronic Resonant Stimulated Raman Scattering Micro-Spectroscopy.

Recently we have reported electronic pre-resonance stimulated Raman scattering (epr-SRS) microscopy as a powerful technique for super-multiplex imaging ( Wei, L. ; Nature 2017 , 544 , 465 - 470 ). However, under rigorous electronic resonance, background signal, which mainly originates from pump-probe process, overwhelms the desired vibrational signature of the chromophores. Here we demonstrate electronic resonant stimulated Raman scattering (er-SRS) microspectroscopy and imaging through suppression of electronic background and subsequent retrieval of vibrational peaks. We observed a change of the vibrational band shapes from normal Lorentzian, through dispersive shapes, to inverted Lorentzian as the electronic resonance was approached, in agreement with theoretical prediction. In addition, resonant Raman cross sections have been determined after power-dependence study as well as Raman excitation profile calculation. As large as 10 cm of resonance Raman cross section is estimated in er-SRS, which is about 100 times higher than previously reported in epr-SRS. These results of er-SRS microspectroscopy pave the way for the single-molecule Raman detection and ultrasensitive biological imaging.