Breaking the diffraction limit by saturation in stimulated-Raman-scattering microscopy: A theoretical study

We present a theoretical investigation on the saturation of stimulated Raman scattering (SRS) and propose an application of it to break the diffraction limit in SRS microscopy. In our proposed scheme, a donut-shaped Stokes beam is used to saturate SRS at the rim of a focused Gaussian pump beam; thus the addition of another Gaussian Stokes beam can only induce additional stimulated Raman loss to the pump beam in a small area inside the donut-shaped beam. Resembling stimulated-emission-depletion microscopy, this method can significantly improve the lateral imaging resolution. Compared with the diffraction-limited resolution, theoretical simulations show that it may be possible to double the spatial resolution with a few TW/cm² of laser intensity. Such super-resolution could greatly enhance the advantage of SRS microscopy for potential applications.