Fig. 8
a i Illustration of tip-enhanced dual-wavelength nanofocused CARS on a multi-walled carbon nanotube (MWCNT). a ii Energy diagram for ω-CARS and 2ω-CARS. When the difference frequency between pump and Stokes light matches the vibrational mode of the molecule, it is resonantly excited. When ω and 2ω-probe light is simultaneously incident within the dephasing time, ω- and 2ω-CARS photons are respectively generated. b i Simultaneous topographical 2ω-CARS imaging of a MWCNT. b ii Composite image of three 2ω-CARS images of the MWCNT using the 2ω-CARS spectrum from D- (red), G- (blue) and 2D- (green) bands. Reprinted with permission from [155]