Self-mixing interferometry and near-field nanoscopy in quantum cascade random lasers at terahertz frequencies

• Published in: Nanophotonics (Berlin, Germany) Vol. 10; no. 5; pp. 1495 - 1503
• Main Authors: Reichel, Kimberly S., Pogna, Eva Arianna Aurelia, Biasco, Simone, Viti, Leonardo, Di Gaspare, Alessandra, Beere, Harvey E., Ritchie, David A., Vitiello, Miriam S.
• Format: Journal Article
• Language: English
• Published: Berlin De Gruyter 01.03.2021; Walter de Gruyter GmbH
• Subjects: Heterostructures; Holes; Interference fringes; Lasers; Microscopes; near field nanoscopy; Near fields; Optical feedback; Optical microscopy; Quantum cascade lasers; random lasers; self-mixing interferometry; Spatial resolution; Spectral emission; Terahertz frequencies; terahertz quantum cascade lasers
• ISSN: 2192-8606; 2192-8614
• DOI: 10.1515/nanoph-2020-0609

We demonstrate that electrically pumped random laser resonators, operating at terahertz (THz) frequencies, and comprising a quantum cascade laser heterostructure, can operate as sensitive photodetectors through the self-mixing effect. We devise two-dimensional cavities exploiting a disordered arrangement of surface holes that simultaneously provide optical feedback and allow light out-coupling. By reflecting the emitted light back onto the surface with random holes pattern, and by varying the external cavity length, we capture the temporal dependence of the laser voltage, collecting a rich sequence of interference fringes that follow the bias-dependent spectral emission of the laser structure. This provides a visible signature of the random laser sensitivity to the self-mixing effect, under different feedback regimes. The latter effect is then exploited, in the near-field, to demonstrate detectorless scattering near-field optical microscopy with nanoscale (120 nm) spatial resolution. The achieved results open up possibilities of detectorless speckle-free nano-imaging and quantum sensing applications across the far-infrared.