Single Pulse Coherent Anti-Stokes Raman Super-Resolved Image Scanning Microscopy

We demonstrate super-resolved coherent vibrational imaging based on single-pulse Coherent Anti-Stokes Raman Scattering (CARS) combined with Image Scanning Microscopy (ISM), enabling label-free vibrational imaging beyond the diffraction limit. As required for coherent imaging, and unlike conventional ISM applied to fluorescence or spontaneous Raman signals, we perform pixel reassignment on the complex optical field rather than the intensity, accounting for the interference-based nature of coherent imaging. In contrast with previous implementations of coherent ISM, here we do not rely on the use of interferometry with an external reference, but rather utilize the intrinsic nonresonant background as reference, while a programmable pulse shaper enables spectral-phase interferometry between the resonant and nonresonant components of the CARS field. After retrieving both the amplitude and the phase of the resonant CARS signal, we apply coherent ISM to achieve resolution enhancement in chemically specific imaging. This technique opens new avenues for high-speed, label-free super-resolved vibrational microscopy and especially for its extension to the low-frequency spectral range and to an implementation in a backscattering geometry.