Scattering type scanning near field optical microscopy with low repetition rate pulsed light source through phase domain sampling
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.
Nature communications