Abstract
Spectral fingerprints of molecules are mostly accessible in the terahertz (THz) and mid-infrared ranges, such that efficient molecular-detection technologies rely on broadband coherent light sources at such frequencies. If THz Quantum Cascade Lasers can achieve octave-spanning bandwidth, their tunability and wavelength selectivity are often constrained by the geometry of their cavity. Here we introduce an adaptive control scheme for the generation of THz light in Quantum Cascade Random Lasers, whose emission spectra are reshaped by applying an optical field that restructures the permittivity of the active medium. Using a spatial light modulator combined with an optimization procedure, a beam in the near infrared (NIR) is spatially patterned to transform an initially multi-mode THz random laser into a tunable single-mode source. Moreover, we show that local NIR illumination can be used to spatially sense complex near-field interactions amongst modes. Our approach provides access to new degrees of freedom that can be harnessed to create broadly-tunable sources with interesting potential for applications like self-referenced spectroscopy.
Highlights
Spectral fingerprints of molecules are mostly accessible in the terahertz (THz) and midinfrared ranges, such that efficient molecular-detection technologies rely on broadband coherent light sources at such frequencies
Transitions correspond to narrow absorption lines, which, in order to be probed, rely on carefully designed THz quantum cascade laser (QCL) sources that are manufactured through highprecision processes
Since gain competition and spatial hole burning are actively present in the selection or suppression of lasing modes in QCLs, quantum cascade random lasers (QCRLs) represent a promising playground to collect information about nonlinear interactions among modes
Summary
Spectral fingerprints of molecules are mostly accessible in the terahertz (THz) and midinfrared ranges, such that efficient molecular-detection technologies rely on broadband coherent light sources at such frequencies. We introduce an adaptive control scheme for the generation of THz light in Quantum Cascade Random Lasers, whose emission spectra are reshaped by applying an optical field that restructures the permittivity of the active medium. Harnessing the many degrees of freedom available in the spatial pattern of the NIR beam, our approach demonstrates an all-optical controllability in QCRLs, which enables the reshaping of THz light to realize unconventional spectral features like bi-color emission. We envision that this technique can be straightforwardly extended to tune other properties like lasing directivity
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