Electronic Preresonance Stimulated Raman Scattering Spectromicroscopy Using Multiple-Plate Continuum

Stimulated Raman scattering (SRS) spectromicroscopy isa powerfultechnique that enables label-free detection of chemical bonds withhigh specificity. However, the low Raman cross section due to typicalfar-electronic resonance excitation seriously restricts the sensitivityand undermines its application to bio-imaging. To address this bottleneck,the electronic preresonance (EPR) SRS technique has been developedto enhance the Raman signals by shifting the excitation frequencytoward the molecular absorption. A fundamental weakness of the previousdemonstration is the lack of dual-wavelength tunability, making EPR-SRSonly applicable to a limited number of species in the proof-of-conceptexperiment. Here, we demonstrate the EPR-SRS spectromicroscopy usinga multiple-plate continuum (MPC) light source able to examine a singlevibration mode with independently adjustable pump and Stokes wavelengths.In our experiments, the C UC vibration mode of Alexa 635 isinterrogated by continuously scanning the pump-to-absorption frequencydetuning throughout the entire EPR region enabled by MPC. The resultsexhibit 150-fold SRS signal enhancement and good agreement with theAlbrecht A-term preresonance model. Signal enhancement is also observedin EPR-SRS images of the whole Drosophila brain stainedwith Alexa 635. With the improved sensitivity and potential to implementhyperspectral measurement, we envision that MPC-EPR-SRS spectromicroscopycan bring the Raman techniques closer to a routine in bio-imaging.