Frequency-modulation stimulated Raman scattering microscopy with an acousto-optic tunable filter

Stimulated Raman scattering (SRS) microscopy is increasingly employed for highly specific, label-free, and high-speed bioimaging. Despite its benefits, SRS is susceptible to spurious background signals caused by competing effects, which lower the possible imaging contrast and sensitivity. An efficient approach to suppress these undesired background signals is frequency-modulation (FM) SRS, which exploits the competing effects’ weak spectral dependence compared to the SRS signal’s high spectral specificity. We propose an FM-SRS scheme realized with an acousto-optic tunable filter, which presents a few advantages compared to other solutions presented in the literature. In particular, it can perform automated measurements from the fingerprint to the CH-stretching region of the vibrational spectrum without any manual adjustment of the optical setup. Moreover, it allows simple all-electronic control of the spectral separation and relative intensities of the pair of probed wavenumbers.