Heterodyne mixing of two far-infrared quantum cascade lasers by use of a point-contact Schottky diode

Barbieri, Stefano; Alton, Jesse; Beere, Harvey E.; Linfield, E. H.; Ritchie, D. A.; Withington, S.; Scalari, Giacomo; Ajili, Lassaad; Faist, Jérôme

doi:10.1364/ol.29.001632

Cited by 56 publications

(32 citation statements)

References 9 publications

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“…The measured full width half maximum (FWHM) of about 40 kHz is in good agreement with previous independent results 27,28 and with our previous measurements of the frequency-noise power spectral density of the same device 17 . It provides a quantitative estimation of the spectral purity of the laser emission over a 1 ms timescale, whereas on longer timescales the jitter of the QCL frequency obviously leads to broader signals.…”

Section: Terahertz Fcs Generationsupporting

confidence: 91%

Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers

Consolino

Taschin

Bartolini³

et al. 2012

Nat Commun

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113

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optical frequency comb synthesizers have represented a revolutionary approach to frequency metrology, providing a grid of frequency references for any laser emitting within their spectral coverage. Extending the metrological features of optical frequency comb synthesizers to the terahertz domain would be a major breakthrough, due to the widespread range of accessible strategic applications and the availability of stable, high-power and widely tunable sources such as quantum cascade lasers. Here we demonstrate phase-locking of a 2.5 THz quantum cascade laser to a free-space comb, generated in a Linbo 3 waveguide and covering the 0.1-6 THz frequency range. We show that even a small fraction ( < 100 nW) of the radiation emitted from the quantum cascade laser is sufficient to generate a beat note suitable for phase-locking to the comb, paving the way to novel metrological-grade terahertz applications, including high-resolution spectroscopy, manipulation of cold molecules, astronomy and telecommunications.

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Section: Terahertz Fcs Generationsupporting

confidence: 91%

Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers

Consolino

Taschin

Bartolini³

et al. 2012

Nat Commun

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113

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“…Thermal drift, in particular, can result in frequency drifts on the order of several MHz over time-scale of seconds [20,21]. In our system the ±100 mK instability of the heat-sink temperature corresponds to a maximum frequency drift of ~10 MHz.…”

mentioning

confidence: 85%

Three-dimensional terahertz imaging using swept-frequency feedback interferometry with a quantum cascade laser

Keeley¹,

Dean²,

Valavanis³

et al. 2015

Opt. Lett.

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Abstract:We demonstrate coherent three-dimensional terahertz imaging by frequency modulation of a quantum cascade laser in a compact and experimentally simple self-mixing scheme. Through this approach we can realize significantly faster acquisition rates compared to previous schemes employing longitudinal mechanical scanning of a sample. We achieve a depth resolution of better than 0.1 m with a power noise spectral density below −50 dB/Hz, for a sampling time of 10 ms/pixel.

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“…3 A LW as small as 20 kHz was observed. 7 When averaged for a longer time period, however, the single LWs in those experiments could exceed 1 MHz due to fluctuations of temperature and bias current, which affect the refractive index of the laser gain medium. Here we report the demonstration of phase locking of the beat signal of a two lateral-mode terahertz QCL to a microwave reference.…”

mentioning

confidence: 93%

“…5 were unstabilized and could be measured only for a short sweep time of ϳ3 ms. They were measured using roomtemperature Schottky diodes to mix signals from a terahertz QCL and a FIR gas laser, 6 two terahertz QCLs, 7 or two longitudinal emission modes of a single QCL. 3 A LW as small as 20 kHz was observed.…”

mentioning

confidence: 99%

Phase locking and spectral linewidth of a two-mode terahertz quantum cascade laser

Baryshev

Hovenier

Adam

et al. 2006

Applied Physics Letters

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We have studied the phase locking and spectral linewidth of an ϳ2.7 THz quantum cascade laser by mixing its two lateral lasing modes. The beat signal at about 8 GHz is compared with a microwave reference by applying conventional phase lock loop circuitry with feedback to the laser bias current. Phase locking has been demonstrated, resulting in a narrow beat linewidth of less than 10 Hz. Under frequency stabilization we find that the terahertz line profile is essentially Lorentzian with a minimum linewidth of ϳ6.3 kHz. Power dependent measurements suggest that this linewidth does not approach the Schawlow-Townes limit. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2227624͔ Significant progress has made terahertz quantum cascade lasers 1 ͑QCLs͒ promising coherent solid-state sources for various applications in spectroscopy, sensing, and imaging. As demonstrated at several frequencies, a terahertz QCL can be used as a local oscillator ͑LO͒ for a heterodyne receiver 2,3 which is a crucial instrument for astronomical and atmospheric high-resolution spectroscopy. For those applications a narrow emission linewidth ͑LW͒ from a QCL under frequency stabilization is essential. In the case of a heterodyne space interferometer, 4 phase locking to an external reference is also required.Ideally, phase locking of the terahertz QCL would take place with respect to a harmonic of a microwave reference signal; however, it has not yet been demonstrated. Recent work has demonstrated frequency locking of a QCL to a far-infrared ͑FIR͒ gas laser line at 3.105 THz. 5 This same work demonstrated a lasing LW of 65 kHz, which could be maintained indefinitely as a result of the frequency stabilization. The LWs of QCLs that were reported earlier than Ref. 5 were unstabilized and could be measured only for a short sweep time of ϳ3 ms. They were measured using roomtemperature Schottky diodes to mix signals from a terahertz QCL and a FIR gas laser, 6 two terahertz QCLs, 7 or two longitudinal emission modes of a single QCL. 3 A LW as small as 20 kHz was observed. 7 When averaged for a longer time period, however, the single LWs in those experiments could exceed 1 MHz due to fluctuations of temperature and bias current, which affect the refractive index of the laser gain medium. Here we report the demonstration of phase locking of the beat signal of a two lateral-mode terahertz QCL to a microwave reference. Additionally, under frequency stabilization conditions we are able to study the emission spectrum of the terahertz QCL as a function of the laser power, in order to investigate the nature of the limit to its LW.We use a terahertz QCL based on the resonant phonon design 8 with an active region containing 176 GaAs/ Al 0.15 Ga 0.85 As quantum-well modules and having a total thickness of 10 m. The cavity of the QCL is a doublesided metal waveguide, which is 40 m wide and 1 mm long. In order to facilitate the experiment described in this letter, we specifically selected a laser with two closely spaced lasing modes. When operated in cw mode ...

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Heterodyne mixing of two far-infrared quantum cascade lasers by use of a point-contact Schottky diode

Cited by 56 publications

References 9 publications

Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers

Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers

Three-dimensional terahertz imaging using swept-frequency feedback interferometry with a quantum cascade laser

Phase locking and spectral linewidth of a two-mode terahertz quantum cascade laser

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