Chirp modulation stimulated Raman scattering microscopy

Coherent Raman microscopy, a rapid, chemical-specific, label-free imaging method, can be plagued by non-Raman background signals. Existing modulation schemes mitigate these but none remove all background signals. Here we demonstrate what we believe to be a novel scheme, chirp modulation stimulated Raman scattering (CM-SRS), based upon modulating uniquely the relative sign of the quadratic phase (linear chirp) of the input lasers. CM-SRS removes all non-Raman signals and is linear in both Raman oscillator strength and concentration. We demonstrate that CM-SRS is highly sensitive, quantitative, and background-free via imaging of traditionally challenging samples and the small molecule pharmacokinetics of single living cells.