Time-resolved scanning near-field optical microscopy with supercontinuum light pulses generated in microstructure fiber

A novel apparatus for time-resolved near-field optical microscopy is described. The apparatus consists of a mode-locked Ti:sapphire laser, a microstructure fiber, and a scanning near-field optical microscope equipped with an apertured optical fiber probe. The probe pulses in visible to near-infrared regions are generated by focusing laser pulses in the microstructure fiber. The broadband continuum can be used as a wavelength-tunable light source for fluorescence excitation as well as for probing absorption of excited states at arbitrary wavelengths by applying pump-probe scheme, in high spatial-resolution (∼100 nm) predominantly determined by the aperture size of the tip. Time resolution obtained with 740-830 nm probe pulses was in 1-2 ps range, while that with 570 nm pulses was 5 ps without precompensation of the group delay dispersion for the probe pulses. Results on the excited-state dynamics of molecular aggregates are presented.