Picosecond hyperspectral stimulated Raman scattering microscopy below 400 wavenumbers

The low-frequency Raman region below 400 wavenumbers has rich chemical information to identify elements and compounds with low vibrational energies. Such low-frequency vibrational modes are usually probed by spontaneous Raman scattering which has low acquisition speed or femtosecond impulsive Raman scattering that requires ultrashort laser pulse and interferometry. High-speed hyperspectral stimulated Raman scattering (hSRS) microscopy has been developed based on spectral focusing but cannot detect low-frequency vibrational transitions. We extended the frequency range of picosecond hSRS microscopy to measure vibrational transitions below 400 cm-1. Using spectral focusing, we can perform hSRS imaging for a ~200 cm-1 spectral window tunable from 200-4000 cm-1.