Chip-scale, electrically-pumped terahertz (THz) quantum cascade lasers (QCLs) can be employed in scattering-type scanning near-field optical microscopy (s-SNOM) to image the response of organic and inorganic materials with nanometer spatial resolution and tomographic sensitivity, overcoming the diffraction limit. By exploiting the self-mixing mechanism, QCLs can work as both sources and detectors, being sensitive to the radiation that is re-injected in the laser cavity after interaction with the tip of the s-SNOM microscope. Interestingly, broadband THz QCL frequency combs (FCs) provide hyperspectral sensitivity to THz s-SNOM systems.
The developed technique can be used to perform fundamental investigations at the nanoscale, spanning from inspecting the carrier density distribution in two-dimensional materials, to monitoring the propagation of plasmon–polariton, and phonon–polariton modes with a ~10 nm spatial resolution and over a broad bandwidth. We applied this method to thin films of topological insulators grown by molecular beam epitaxy (MBE), revealing the presence of Dirac surface states by mapping the propagation of surface polaritons.
KEYWORDS: Imaging spectroscopy, Near field, Terahertz radiation, Quantum cascade lasers, Sensors, Near field optics, Hyperspectral imaging, Image sensors, Frequency combs, Super resolution microscopy
We demonstrate the first-ever hyperspectral s-SNOM imaging system, providing 160nm spatial resolution, coherent detection of multiple phase-locked modes and mapping of the THz optical response of nanoscale materials such as topological insulators in the 2.29-3.60 THz range with noise-equivalent-power ~400pW/√Hz, relying on a 6mW comb-emitting THz QCL. We provide near-field images of Bi2Se3 and Bi2Te3 and their spectroscopic characterization in a >1 THz optical bandwidth extracting their optical contrast response through the application of the synthetic optical holography technique.
We report the polarization, the interference far-filed pattern, the multimodal spectral emission and the power extraction of the emitted beam from a set of electrically-pumped random quantum cascade lasers in the terahertz range. By integrating, on chip, a non-linear multilayer graphene stack with the laser gain medium, we demonstrate self-induced phase-coherence between the naturally incoherent random modes. We then employ the devised random laser in a detectorless near-field imaging system, exploiting the intracavity reinjection of the laser field via self-mixing interferometry in a confocal microscope for speckle-free tomography with nm-size resolution
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.