Stimulated Raman scattering microscopy with spectral focusing of 2-ps laser pulses for higher spectral resolution and signal-to-background ratio

We propose the use of 14 ps chirped laser pulses in stimulated Raman scattering (SRS) microscopy to improve the spectral resolution and signal-to-background ratio (SBR) in SRS imaging. We developed a single-grating-based pulse chirper and implemented it into an intensity-modulation SRS microscope to stretch the excitation pulse width from 2 to 14 ps. We confirmed that the 14 ps pulses provide a spectral resolution of 2 cm-1 by measuring the SRS spectra of diamond crystals. We found that the 14 ps pulses have smaller nonlinear background signals and improve SBR in SRS imaging of various samples due to the instantaneous narrow-band excitation and low peak power. Our technique can broaden the application of the 2 ps intensity modulation SRS microscopy by improving the spectral resolution and sensitivity.