A theoretical study of diffraction limit breaking via coherent control of the relative phase in coherent anti-Stokes Raman scattering microscopy

We present a theoretical investigation of how coherent control of the relative phase in coherent anti-Stokes Raman scattering (CARS) microscopy can break the diffraction limit. In quantum theory, it is found that the relative phase of the pump and Stokes pulses can be used to periodically tune the intensity of the anti-Stokes signal. Thus, by controlling the relative phase around the center of the pump and Stokes pulses, the anti-Stokes signal can be tuned to zero in this region. In turn, the useful spot-generating anti-Stokes signal is substantially suppressed to a much smaller dimension, and scanning of the spots renders CARS images with sub-diffraction resolutions. Such super-resolutions can greatly enhance the advantage of using CARS microscopy in many potential applications.