For developing diffraction-unlimited Raman microscopy, a three-beam femtosecond stimulated Raman scattering (SRS) is deviced for simultaneously inducing two different SRS processes associated with Raman-active modes in the same molecule. Two SR gains involving a common pump pulse and two separate Stokes beams are coupled and compete: one SRS is selectively suppressed as the other Stokes beam intensities increases. Our theoretical description and experimental evidence support that the selective suppression behavior is due to the limited number of pump photos used for both of the two SRS processes. We anticipate a potential of this new switching-off concept in super-resolution label-free microscopy.
Recent development of super-resolution fluorescence imaging technique such as stochastic optical reconstruction
microscopy (STORM) and photoactived localization microscope (PALM) has brought us beyond the diffraction limits. It
allows numerous opportunities in biology because vast amount of formerly obscured molecular structures, due to lack of
spatial resolution, now can be directly observed. A drawback of fluorescence imaging, however, is that it lacks complete
structural information. For this reason, we have developed a super-resolution multimodal imaging system based on
STORM and full-field optical coherence microscopy (FF-OCM). FF-OCM is a type of interferometry systems based on a
broadband light source and a bulk Michelson interferometer, which provides label-free and non-invasive visualization of
biological samples. The integration between the two systems is simple because both systems use a wide-field
illumination scheme and a conventional microscope. This combined imaging system gives us both functional
information at a molecular level (~20nm) and structural information at the sub-cellular level (~1μm). For thick samples
such as tissue slices, while FF-OCM is readily capable of imaging the 3D architecture, STORM suffer from aberrations
and high background fluorescence that substantially degrade the resolution. In order to correct the aberrations in thick
tissues, we employed an adaptive optics system in the detection path of the STORM microscope. We used our
multimodal system to obtain images on brain tissue samples with structural and functional information.