Heterogeneous, terahertz quantum cascade lasers with thermally tunable frequency comb operation

We report on the engineering of broadband quantum cascade lasers (QCLs) emitting at Terahertz (THz) frequencies, which exploit a heterogeneous active region scheme and have a current density dynamic range (Jdr) of 3.2, significantly larger than the state of the art, over a 1.3 THz bandwidth. We demonstrate that the devised broadband lasers operate as THz optical frequency comb synthesizers in continuous-wave, with a maximum optical output power of 4 mW. Measurement of the intermode beatnote map reveals a clear dispersion-compensated frequency comb regime with a corresponding emission bandwidth of ≈ 1.05 THz and a stable and narrow (4.15 KHz) beatnote. Analysis of the electrical and thermal beatnote tuning reveals a current-tuning coefficient ranging between 5 MHz/mA and 2.1 MHz/mA and a temperature-tuning coefficient of –4 MHz/K. The ability to tune the THz QCL combs over their full dynamic range by temperature and current paves the way for their use as a powerful spectroscopy tool that can provide broad frequency coverage combined with high
precision spectral accuracy.

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