Phase-resolved terahertz self-detection nearfield microscopy
M. C. Giordano, S. Mastel, C. Liewald, L. L. Columbo, M. Brambilla, L. Viti, A. Politano, K. Zhang, L. Li, A. G. Davies, E. H. Linfield, R. Hillenbrand, F. Keilmann, G. Scamarcio and M, S. Vitiello
Optics Express 26, 18423 (2018)
At terahertz (THz) frequencies, scattering-type scanning near-field optical
microscopy (s-SNOM) based on continuous wave sources mostly relies on cryogenic and
bulky detectors, which represents a major constraint for its practical application. Here, we
devise a THz s-SNOM system that provides both amplitude and phase contrast and achieves
nanoscale (60-70nm) in-plane spatial resolution. It features a quantum cascade laser that
simultaneously emits THz frequency light and senses the backscattered optical field through a
voltage modulation induced inherently through the self-mixing technique. We demonstrate its
performance by probing a phonon-polariton-resonant CsBr crystal and doped black
phosphorus flakes.