The detection sensitivity of SRS microscopy is fundamentally limited by shot noise. To address this barrier, we revisit SRS from the perspective of energy deposition. The SRS process pumps molecules to their vibrational excited states. The thereafter relaxation heats up the surrounding and induces a change in refractive index, as suggested by simulation and fluorescence thermometer measurement. By introducing a CW laser beam to probe the refractive index change, we demonstrate stimulated Raman photothermal (SRPT) imaging of particles, cells, and tissues with high signal to noise ratio at the fingerprint region. SRPT microscopy opens a new way to vibrational spectroscopic imaging with ultrahigh sensitivity.
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