Terahertz laser frequency combs


Terahertz light can be used to identify numerous complex molecules, but has traditionally remained unexploited due to the lack of powerful broadband sources. Pulsed lasers can be used to generate broadband radiation, but such sources are bulky and produce only microwatts of average power. Conversely, although terahertz quantum cascade lasers are compact semiconductor sources of high-power terahertz radiation, their narrowband emission makes them unsuitable for complex spectroscopy. In this work, we demonstrate frequency combs based on terahertz quantum cascade lasers, which combine the high power of lasers with the broadband capabilities of pulsed sources. By fully exploiting the quantum-mechanically broadened gain spectrum available to these lasers, we can generate 5 mW of terahertz power spread across 70 laser lines. This radiation is sufficiently powerful to be detected by Schottky-diode mixers, and will lead to compact terahertz spectrometers.

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Figure 1: GVD of laser gain medium.
Figure 2: Continuous-wave spectrum and beat notes.
Figure 3: Results of SWIFT measurement.
Figure 4: Bias dependence of beat-note and SWIFT spectra.
Figure 5: Heterodyne beat note between single-mode laser and comb.


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The work at MIT was supported by NASA and the NSF. The work in the Netherlands was supported by NWO, NATO SFP and RadioNet. This work was performed, in part, at the Center for Integrated Nanotechnologies, a US Department of Energy, Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multi-programme laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration (contract no. DE-AC04-94AL85000). The authors thank D. Levonian for his help in setting up the FTIR.

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D.B. conceived the strategy, designed the devices, performed the measurements and completed the analysis. D.B. and N.H. performed electromagnetic simulations. T.-Y.K., N.H. and C.W.I.C. fabricated the devices. D.B., X.C. and Y.Y. performed the heterodyne beat-note measurements. D.J.H. and J.-R.G. provided the hot electron bolometer mixer. J.L.R. provided the material growth. All work was performed under the supervision of Q.H.

Corresponding author

Correspondence to David Burghoff.

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The authors declare no competing financial interests.

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Burghoff, D., Kao, T., Han, N. et al. Terahertz laser frequency combs. Nature Photon 8, 462–467 (2014). https://doi.org/10.1038/nphoton.2014.85

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