Rapid large-area multiphoton microscopy for characterization of graphene.

Single- and few-layer graphene was studied with simultaneous third-harmonic and multiphoton-absorption-excited fluorescence microscopy using a compact 1.55 μm mode-locked fiber laser source. Strong third-harmonic generation (THG) and multiphoton-absorption-excited fluorescence (MAEF) signals were observed with high contrast over the signal from the substrate. High contrast was also achieved between single- and bilayer graphene. The measurement is straightforward and very fast compared to typical Raman mapping, which is the conventional method for characterization of graphene. Multiphoton microscopy is also proved to be an extremely efficient method for detecting certain structural features in few-layer graphene. The accuracy and speed of multiphoton microscopy make it a very promising characterization technique for fundamental research as well as large-scale fabrication of graphene. To our knowledge, this is the first time simultaneous THG and MAEF microscopy has been utilized in the characterization of graphene. This is also the first THG microscopy study on graphene using the excitation wavelength of 1.55 μm, which is significant in telecommunications and signal processing.