Evidence for frequency comb emission from a Fabry-Pérot terahertz quantum-cascade laser

Wienold, Martin; Röben, Benjamin; Schrottke, L.; Grahn, H. T.

doi:10.1364/oe.22.030410

Cited by 51 publications

(47 citation statements)

References 29 publications

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“…However, small amounts of light can perturb the laser bias. 21,26,27 The ultrafast dynamics allows the THz QCL to act as an efficient ultrafast detector, bypassing the need for an integrated Schottky diode as was done in Ref. 28.…”

mentioning

confidence: 99%

“…26,34,35 In an other experiment, the feedback from a Fourier-Transform Interferometer (FTIR) was used to probe the comb characteristics of a THz QCL. 21 In our case, we are not relying on self-mixing, but the radiation of the neighbor laser (sample laser) is coupled in the detector laser which acts also as LO for the multi-heterodyne signal (Figure 1(a)). The multiheterodyne mixing of the two laser signals is then visible as a fast modulation on the laser bias of the LO laser.…”

mentioning

confidence: 99%

“…In addition, also the intermode beating signal of both lasers corresponding to their repetition frequencies is captured. As self-mixing due to reflections would reduce the stability of the combs, [18][19][20][21]36 we avoided reflections by blocking the optical beam of the combs with absorbing cardboard.…”

mentioning

confidence: 99%

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On-chip, self-detected terahertz dual-comb source

Rösch

Scalari

Villares

et al. 2016

Applied Physics Letters

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We present a directly generated on-chip dual-comb source at terahertz (THz) frequencies. The multi-heterodyne beating signal of two free-running THz quantum cascade laser frequency combs is measured electrically using one of the combs as a detector, fully exploiting the unique characteristics of quantum cascade active regions. Up to 30 modes can be detected corresponding to a spectral bandwidth of 630 GHz, being the available bandwidth of the dual comb configuration. The multi-heterodyne signal is used to investigate the equidistance of the comb modes showing an accuracy of 10−12 at the carrier frequency of 2.5 THz.

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confidence: 99%

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confidence: 99%

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On-chip, self-detected terahertz dual-comb source

Rösch

Scalari

Villares

et al. 2016

Applied Physics Letters

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“…This second coherence property is linked to the comb offset frequency fceo. , PDI [73], Harvard [37], ENS [50], MIT [70].…”

Section: Comb Coherencementioning

confidence: 99%

“…Another technique has been proposed to assess the degree of coherence of THz QCL combs. It is based on self-mixing of the laser output which is fed back into the laser cavity after being filtered by a FTIR [73].…”

Section: Intermode Beat Spectroscopy and Swiftsmentioning

confidence: 99%

Quantum Cascade Laser Frequency Combs

Faist

Villares²,

Scalari³

et al. 2016

Nanophotonics

193

137

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It was recently demonstrated that broadband quantum cascade lasers can operate as frequency combs. As such, they operate under direct electrical pumping at both mid-infrared and THz frequencies, making them very attractive for dual-comb spectroscopy. Performance levels are continuously improving, with average powers over 100 mW and frequency coverage of 100 cm −1 in the midinfrared region. In the THz range, 10 mW of average power and 600 GHz of frequency coverage are reported. As a result of the very short upper state lifetime of the gain medium, the mode proliferation in these sources arises from four-wave mixing rather than saturable absorption. As a result, their optical output is characterized by the tendency of small intensity modulation of the output power, and the relative phases of the modes to be similar to the ones of a frequency modulated laser. Recent results include the proof of comb operation down to a metrological level, the observation of a Schawlow-Townes broadened linewidth, as well as the first dual-comb spectroscopy measurements. The capability of the structure to integrate monothically nonlinear optical elements as well as to operate as a detector shows great promise for future chip integration of dual-comb systems.

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Self‐Induced Phase Locking of Terahertz Frequency Combs in a Phase‐Sensitive Hyperspectral Near‐Field Nanoscope

et al. 2022

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Chip-scale, electrically-pumped terahertz (THz) frequency-combs (FCs) rely on nonlinear four-wave-mixing processes, and have a nontrivial phase relationship between the evenly spaced set of emitted modes. Simultaneous monitoring and manipulation of the intermode phase coherence, without any external seeding or active modulation, is a very demanding task for which there has hitherto been no technological solution. Here, a self-mixing intermode-beatnote spectroscopy system is demonstrated, based on THz quantum cascade laser FCs, in which light is back-scattered from the tip of a scanning near-field optical-microscope (SNOM) and the intracavity reinjection monitored. This enables to exploit the sensitivity of FC phase-coherence to optical feedback and, for the first time, manipulate the amplitude, linewidth and frequency of the intermode THz FC beatnote using the feedback itself. Stable phase-locked regimes are used to construct a FC-based hyperspectral, THz s-SNOM nanoscope. This nanoscope provides 160 nm spatial resolution, coherent detection of multiple phase-locked modes, and mapping of the THz optical response of nanoscale materials up to 3.5 THz, with noise-equivalent-power (NEP) ≈400 pW √Hz −1 . This technique can be applied to the entire infrared range, opening up a new approach to hyper-spectral near-field imaging with wide-scale applications in the study of plasmonics and quantum science, inter alia.

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Evidence for frequency comb emission from a Fabry-Pérot terahertz quantum-cascade laser

Cited by 51 publications

References 29 publications

On-chip, self-detected terahertz dual-comb source

On-chip, self-detected terahertz dual-comb source

Quantum Cascade Laser Frequency Combs

Self‐Induced Phase Locking of Terahertz Frequency Combs in a Phase‐Sensitive Hyperspectral Near‐Field Nanoscope

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