Differential imaging in coherent anti-Stokes Raman scattering microscopy with LaguerreGaussian excitation beams

We propose a new differential imaging technique to visualize the fine structures and the edges of a sample in coherent anti-Stokes Raman Scattering (CARS) microscopy. Both the pump and Stokes excitation fields are modulated simultaneously with a spiral phase mask which transforms them from Gaussian modes into Laguerre-Gaussian modes of LG0l for CARS excitation. With an accurate three dimensional finite-difference timedomain (FDTD) method, the intensity and phase distributions of focused input fields, the scattering pattern of generated CARS signal as well as the formation of differential images are studied detailedly, and by simulating the sensitivity range and reliability of this method, we have verified that it is much suitable for visualizing structures with a scale comparable to the excitation wavelength and has higher reliability in retrieving chemical structural information of the sample compared to common CARS microscopy.