title: Scattering-type scanning near-field optical microscopy with low-repetition-rate pulsed light source through phase-domain sampling.
abstract: Scattering-type scanning near-field optical microscopy (s-SNOM) allows spectroscopic imaging with spatial resolution below the diffraction limit. With suitable light sources, s-SNOM is instrumental in numerous discoveries at the nanoscale. So far, the light sources have been limited to continuous wave or high-repetition-rate pulsed lasers. Low-repetition-rate pulsed sources cannot be used, due to the limitation of the lock-in detection mechanism that is required for current s-SNOM techniques. Here, we report a near-field signal extraction method that enables low-repetition-rate pulsed light sources. The method correlates scattering signals from pulses with the mechanical phases of the oscillating s-SNOM probe to obtain near-field signal, by-passing the apparent restriction imposed by the Nyquist-Shannon sampling theorem on the repetition rate. The method shall enable s-SNOM with low-repetition-rate pulses with high-peak-powers, such as femtosecond laser amplifiers, to facilitate investigations of strong light-matter interactions and nonlinear processes at the nanoscale.
authors.affiliation: Department of Chemistry, Lehigh University, 6 E Packer Avenue, Bethlehem, Pennsylvania 18015, USA.
authors.forename: Haomin
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Lehigh University, 6 E Packer Avenue, Bethlehem, Pennsylvania 18015, USA.
authors.forename: Le
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Lehigh University, 6 E Packer Avenue, Bethlehem, Pennsylvania 18015, USA.
authors.forename: Xiaoji G
authors.identifier: 0000-0003-0847-5871
authors.initials: XG
authors.lastname: Xu