Recent progress in terahertz difference-frequency quantum cascade laser sources

Kazuue Fujita, Seungyong Jung, Yifan Jiang, Jae Hyun Kim, Atsushi Nakanishi, Akio Ito, Masahiro Hitaka, Tadataka Edamura, Mikhail A. Belkin

Research output: Contribution to journalArticlepeer-review

74 Scopus citations


Terahertz quantum cascade laser (QCL) sources based on intra-cavity difference frequency generation are currently the only electrically pumped monolithic semiconductor light sources operating at room temperature in the 1-6-THz spectral range. Relying on the active regions with the giant second-order nonlinear susceptibility and the Cherenkov phase-matching scheme, these devices demonstrated drastic improvements in performance in the past several years and can now produce narrow-linewidth single-mode terahertz emission that is tunable from 1 to 6 THz with power output sufficient for imaging and spectroscopic applications. This paper reviews the progress of this technology. Recent efforts in wave function engineering using a new active region design based on a dual-upper-state concept led to a significant enhancement of the optical nonlinearity of the active region for efficient terahertz generation. The transfer of Cherenkov devices from their native semi-insulating InP substrates to high-resistivity silicon substrates resulted in a dramatic improvement in the outcoupling efficiency of terahertz radiation. Cherenkov terahertz QCL sources based on the dual-upper-state design have also been shown to exhibit ultra-broadband comb-like terahertz emission spectra with more than one octave of terahertz frequency span. The broadband terahertz QCL sources operating in continuous-wave mode produces the narrow inter-mode beat-note linewidth of 287 Hz, which indicates frequency comb operation of mid-infrared pumps and thus supports potential terahertz comb operation. Finally, we report the high-quality terahertz imaging obtained by a THz imaging system using terahertz QCL sources based on intra-cavity difference frequency generation.

Original languageEnglish
Pages (from-to)1795-1817
Number of pages23
Issue number11
StatePublished - 1 Nov 2018
Externally publishedYes


  • difference frequency generation
  • integrated optics devices
  • intersubband transitions
  • quantum cascade laser
  • terahertz


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