Tip-enhanced broadband CARS spectroscopy and imaging using a photonic crystal fiber based broadband light source

We report tip-enhanced broadband coherent anti-Stokes Raman scattering (CARS) spectroscopy and imaging based on a broadband light source using a photonic crystal fiber. Multiplexing from 900 cm^-1 to 2200 cm ^-1 is achieved by optimizing the supercontinuum generation process at a high numerical aperture focus. By combining this system with a shear-force microscope, semiconducting carbon nanotubes are imaged with a spatial resolution of 60 nm. Our results show that tip-enhanced broadband CARS image exhibits a positive contrast even though the enhancement effect has not been fully optimized. Analyses of delay-dependent tip-enhanced broadband CARS spectra suggest the possibilities of multiple carrier interactions that uniquely occur at high intensities within the nanotubes.