Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photon-driven broadband emission and RF injection locking of THz quantum
  cascade laser frequency combs   We present homogeneous quantum cascade lasers (QCLs) emitting around 3 THz
which display bandwidths up to 950 GHz with a single stable beatnote. Devices
are spontaneously operating in a harmonic comb state, and when in a dense mode
regime they can be injection locked at the cavity roundtrip frequency with very
small RF powers down to -55 dBm. When operated in the electrically unstable
region of negative differential resistance, the device displays ultra-broadband
operation exceeding 1.83 THz ($\Delta f/f=50\%$) with high phase noise,
exhibiting self-sustained, periodic voltage oscillations. The low CW threshold
(115 A$\cdot$ cm$^{-2}$) and broadband comb operation ($\Delta f/f=25\%$) make
these sources extremely appealing for on-chip frequency comb applications.

36
The categories of this paper are: cmp-lg
23
The categories of this paper are: solv-int
2
The categories of this paper are: math
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
7
The categories of this paper are: hep-th