Fig. 1. Design of SR-SRS microscopy. (a) Optical layout of SR-SRS; (b) spatial profiles of the visible beam before and after VR; (c) PSF of donut-shaped visible beam and UV beam; and (d) schematic diagram of the depleted and activated SRS at the detection frequency (Ω0) of the closed-ring isomer. Scale bar: 2 mm in (b) and 1μm in (c). VR, vortex retarder; EOM, electro-optical modulator; LIA, lock-in amplifier; OB, objective; Con, condenser; DM, dichroic mirror; SM, single-mode fiber; PD, photodiode; F, filter; PC, personal computer; DS, delay stage; SU, scanning unit; SL, scan lens; and TL, tube lens.

Fig. 2. Properties of photoswitchable Raman probe and SR-SRS imaging of native probe molecules. (a) SRS spectra of DTE-Ph in the open- and closed-ring isomers upon visible and UV light; (b) SRS signal of DTE-Ph acquired at the UV-induced Raman frequency (2194cm−1) shows on/off switching behavior under UV/visible pulsed irradiations; (c) relationship of on-switching transition time under different powers of the UV beam; (d) SRS signal depletion under different visible laser powers and fixed 20μW UV power; (e) SRS and (f) SR-SRS images of the probe powder; and (g), (h) normalized intensity profiles along the line cuts in (e) and (f). Scale bar: 1μm.

Fig. 3. SR-SRS imaging of synthesized DTE-Ph NPs. (a) Schematics of NP synthesis; (b) size distribution of NPs determined by DLS; (c) SRS and SR-SRS images of the NPs spread on glass slide; (d) zoom-in images of the labeled rectangle regions in (c) and data fitted by Gaussian function of the single dots pointed with green arrowheads; (e) SRS and SR-SRS images of the NPs; (f) intensity profile along the lines marked in (e); and (g) statistical analysis of multiple particles (n=10). Scale bar: 2μm in (c), (e) and 500 nm in (d).

Fig. 4. SR-SRS imaging of live cells. (a), (c) SRS images of NPs treated HeLa cells at different Raman frequencies: CH2 symmetric stretch (2850cm−1), CH3 symmetric stretch (2930cm−1), alkyne stretches of the closed-ring (2194cm−1) isomers, and corresponding SR-SRS at the activate frequency (2194cm−1). (b), (d) Data fitted by Gaussian function of the dots pointed with green arrowheads in (a) and (b). Scale bar: 20μm in zoom-out images and 2μm in zoom-in images.