Nonlinear optical characterization of porous carbon materials by CARS, SHG and TPEF

The Coherent anti-Stokes Raman scattering (CARS) microscopy is employed to characterize porous carbon materials. The slices of two dimensional (2D) CARS images are obtained, using Z-scan technology. Furthermore, the three dimensional (3D) image of CARS is reconstructed with the Z-scanned 2D CARS images. The visualizations of rotation for 3D CARS are also shown. The 2D and 3D CARS images with rotations can clearly characterize the structures and properties of porous carbon materials, including the surface and inner parts. Nonlinear optical second harmonic generation demonstrates the inversion symmetry breaking of porous carbon materials, which is not centrosymmetric material. The two-photon excitation fluorescence image reveals that porous carbon material is of weak auto-fluorescence. The clearly observed signal of two photon-excitation fluorescence provides direct evidence that photon momentum transfer to the electron system occurs. Experimental results demonstrate that the nonlinear optical microscopy is a great optical analysis method for the study of porous carbon materials, and can be potentially used for the optical characterization on the materials at micro-nano-scale.