Electronic pre-resonance stimulated Raman scattering spectromicroscopy driven by a supercontinuum laser source

Stimulated Raman scattering (SRS) techniques enable label-free detection of the vibrational modes of molecules with high chemical specificity. However, its practical application to material characterization and bioimaging has been limited by sensitivity accompanied with the low Raman cross-section issue, resulting from typical far electronic resonance excitation. To address this limitation, the electronic pre-resonance (EPR) SRS technique has been developed to enhance Raman signals through bringing the excitation frequency close enough to the absorption peaks of examined molecules. However, a significant weakness of previous demonstrations was the lack of dual-wavelength tunability, restricting EPR-SRS to only a limited number of species in a proof-of-concept experiment. In this study, we present EPR-SRS spectromicroscopy driven by a multiple-plate continuum (MPC) light source. The MPC light source enables the examination of a single vibration mode with independent adjustment of both pump and Stokes wavelengths. As a proof-of-concept experiment, we interrogated the C=C vibration mode of Alexa 635 by continuously scanning the pump-to-absorption frequency detuning across the entire EPR region. The results exhibit a remarkable 150-fold enhancement in SRS signal and demonstrate good agreement with the Albrecht A-term pre-resonance model. Moreover, we observed signal enhancement in EPR-SRS bioimages of Drosophila brains stained with Alexa 635. Leveraging the improved sensitivity and potential to implement hyperspectral measurement, we envision that this technique holds great promise for advancing our understanding of biological systems and facilitating multiplex chemical characterization.