Raman scattering microscopy offering a label-free, chemical-specific contrast mechanism based on the intrinsic vibrations of chemical bonds or groups is limited in spatial resolution by the optical diffraction limit. We aim to develop a new method for super-resolution Raman imaging by implementing the depletion strategy of STED (Stimulated Emission Depletion) microscopy to a stimulated Raman scattering (SRS) technique. In order to reduce the effective focal spot of a SRS signal, we overlap the focal spot with a donut shaped beam that eliminates SRS signal at the periphery of the focal spot. In order to achieve resolution &lt;100 nm, it is required to device a way to suppress SRS signal with efficiency &gt;40%. Our depletion principle is based on the competition of two different stimulated Raman processes on the same molecule. When two SR gains shares the same pump pulse, the two processes become coupled and complete. We obtained up to 70% efficiency for the depletion of the ring breathing mode of benzene by using the CH stretching mode with 2.1 TW/cm2 of 1026.5 nm. At the biological damage threshold of 1 TW/cm2, the depletion efficiency is 40 % and the expected resolution is 6-fold enhanced from the diffraction limit. As an application of super-resolution SRS microscopy, we are aiming to characterize the distribution of defects and disorder in graphene using the peak shape and intensity of G and D band at 1580 cm-1 and 1350 cm-1, respectively. The ratio of the intensity of D and G peak is closely related to the distance between the defects. We anticipate that super-resolution Raman microscopy can precisely map both the density and doping of graphene defects.

Super-resolution stimulated Raman scattering microscopy

2019 Fall National Meeting

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