Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: All-Optical Adaptive Control of Quantum Cascade Random Lasers   Spectral fingerprints of molecules are mostly accessible in the terahertz and
mid-infrared ranges, such that efficient molecular-detection technologies rely
on broadband coherent light sources at such frequencies. THz Quantum Cascade
Lasers can achieve octave-spanning bandwidths. However, their tunability and
wavelength selectivity is often constrained by the geometry of their cavity.
The recently introduced Quantum Cascade Random Lasers represent alternative
sources of THz light, in which random scattering provides the required field
confinement. The random resonator geometry greatly relaxes wavelength
selectivity, thus producing radiation that is both spectrally broadband and
collimated in the far-field. Yet, the intrinsic randomness of these devices'
spectral emission strongly restricts the scope of their potential applications.
In this work, we demonstrate the all-optical adaptive control and tuning of
Quantum Cascade Random Lasers. The specificity of our random-laser sources is
exploited to locally modify the system's permittivity with a near-infrared
(NIR) laser beam and thereby substantially reconfigure the distribution of
disorder. Using a spatial light modulator combined with an optimization
procedure, the NIR illumination is spatially modulated to reshape the spectral
emission and transform the initially multimode laser into a single mode source,
which could be harnessed to perform self-referenced spectroscopic measurements.
Moreover, we show that local NIR perturbations can be used to sense linear and
nonlinear interactions amongst modes in the near field. Our work points the way
towards the design of broadly tunable THz sources with greatly relaxed
fabrication constraints.

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The categories of this paper are: acc-phys
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The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
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The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
32
The categories of this paper are: atom-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-th
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The categories of this paper are: chem-ph
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The categories of this paper are: supr-con
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The categories of this paper are: cond-mat
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The categories of this paper are: econ
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The categories of this paper are: ao-sci
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The categories of this paper are: funct-an
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The categories of this paper are: stat