Fig. 1. Principle of SIMIP. (a) Schematic of the SIMIP system. (b) Schematic diagram of illumination pattern on the imaging plane. (c) Isotropic extension of OTF by varying the phase and the orientation of the illumination pattern. The red dot represents the projection of the sample in the reciprocal space. (d) Simulated PSF for widefield imaging and SIM imaging, respectively. (e) Modulation of the fluorophore emission intensity by the IR pulse vibrational absorption of nearby molecules. (f) Chemical information obtained using SIMIP.

Fig. 2. Setup and data acquisition process of SIMIP. (a) Setup of SIMIP. SMF, single-mode fiber; SLM, spatial light modulator; HWP, half-wave plate; PBS, polarizing beam splitter; L, lens; M, mirrors; OAP, off-axis parabolic mirror; OBJ, objective; DM, dichroic mirror; sCMOS, scientific complementary metal-oxide semiconductor; QCL, quantum cascade laser. (b) The time scheme of SIMIP. (c) The process of obtaining SIMIP spectra.

Fig. 3. SIMIP imaging performance. (a) SIMIP images of 200-nm PMMA beads at 1730cm−1. (b) Spectra of PMMA film measured by FTIR (blue) and PMMA beads measured by SIMIP (red). int., intensity; abs. absorption; a.u., arbitrary units. (c), (d) SIMIP images of 200-nm PMMA beads at different wavenumbers. (e), (f) The enlarged images of the selected region in panel (a) using SIMIP (e) and F-MIP/F-PTIR (f), respectively. (g) The intensity profiles of a single bead using SIMIP (red) and F-MIP/F-PTIR (black), respectively. (h) The intensity profiles of the PMMA beads images indicated by the white arrows in panels (e) and (f). (i), (j) The frequency domain amplitude images of the same beads using SIMIP (i) and F-MIP/F-PTIR (j). The yellow boxes in panels (i) and (j) highlight the same region.

Fig. 4. Fluorescence and SIMIP images of the mixture of PS beads and PMMA beads. (a), (b) Fluorescence (a) and SIMIP (b) images from the same position in the sample. (c), (d) The enlarged images of the selected region in panels (a) and (b). (e), (f) Standard FTIR spectra of PS (e) and PMMA samples (f), respectively. Vertical lines indicate the selected wavelengths.