4.7 Article

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

Journal

NANOPHOTONICS
Volume 10, Issue 5, Pages 1495-1503

Publisher

WALTER DE GRUYTER GMBH
DOI: 10.1515/nanoph-2020-0609

Keywords

near field nanoscopy; random lasers; self-mixing interferometry; terahertz quantum cascade lasers

Funding

  1. ERC Project [681379]

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This study demonstrates the use of electrically pumped random laser resonators as sensitive photodetectors through the self-mixing effect, and shows the laser sensitivity to self-mixing under different feedback conditions. By utilizing two-dimensional cavities and reflecting emitted light back onto the surface, a near-field optical microscope with 120 nm spatial resolution is achieved, opening up possibilities for speckle-free nano-imaging and quantum sensing applications in the far-infrared region.
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 farinfrared.

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