Ultrashort pulse characterization via scanning ultrafast near-field second harmonic optical microscopy

Probing nanomaterials and nanostructures on the nanometer-femtosecond spatiotemporal scale requires characterizations of ultrashort pulses in the near field. Here we report the measurement of ultrashort pulses at the tip of an apertured fiber probe of a custom-developed near-field scanning optical microscope (NSOM). We show that sub-diffraction limited second harmonic imaging resolution is attainable in the near field while femtosecond pulses are characterized using the collinear frequency resolved optical gating. We compared both near-field and far-field measurements and explored polarized optical response at both the fundamental and the second harmonic frequencies, revealing the NSOM tip has minimal perturbation on ultrafast studies in the near field.