Using complementary optical microscopy techniques provides more detailed insight into biological samples. However, misinterpretation can occur by temporal discrepancies due to differences in temporal resolution and switching imaging modalities. Here, we demonstrated multimodal imaging of cryofixed cells using Raman and fluorescence structured illumination microscopy (SIM). Cryofixation preserves structures and chemical states of samples in their near-native states, allowing multimodal imaging without artifacts caused by temporal discrepancy. We demonstrated multimodal imaging of cryofixed HeLa cells stained with an actin probe, where Raman microscope visualized cytochromes, proteins and lipids, and SIM visualized fluorescence-labelled actin filaments.
Through the combination of nanoscale Mie-resonance and photothermal/thermo-optical effect, the nonlinear index n2 of both plasmonic and metal nanostructure can be enhanced by more than three orders of magnitude. We discovered various types of nonlinearity that include saturation, suppression, and reverse saturation in nanostructures. Through a similar mechanism, we also achieved optical bistability in a nanoscale resonator with a record-low Q-factor (<10) and observed large nonlinearity with hysteretic behavior. These tunable optical nonlinearities with low requirements on sample size and shape open new possibilities for the design of photonic devices and metal/semiconductor super-resolution.
We unraveled a novel optical bistable state in amorphous silicon nanocuboids, featuring an abrupt super-linear jump of scattering intensity during hysteretic switching. The effective intensity dependency reaches 19th power, leading to an nonlinear index n2 as large as 5 μm2/mW, 7-order larger than the bulk value and well explained through coupled electromagnetic and photothermal simulation. Combining the ultralarge super-linear response with dark-field laser scanning microscopy, 3.5-times resolution enhancement was achieved, without any need of temporal/spatial excitation modulation. This hysteresis scattering not only sets a benchmark in optical super-resolution technique, but also suggests further optical signal processing potentials.
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