Terahertz heterodyne receiver with quantum cascade laser and hot electron bolometer mixer in a pulse tube cooler

Richter, Heiko; Semenov, A. D.; Pavlov, S.G.; Mahler, L.; Tredicucci, Alessandro; Beere, Harvey E.; Ritchie, D. A.; Ilin, K.; Siegel, M.; Hübers, Heinz‐Wilhelm

doi:10.1063/1.2988896

Cited by 71 publications

(30 citation statements)

References 19 publications

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“…Emission is then highly polarized, as both the selection rules of the intersubband transitions and the surface-plasmon waveguide design strongly select only TM polarization for lasing. Even if they require cooling to low temperatures, this can easily be achieved by low vibration, cryogen-free devices, like pulse tube and Sterling coolers [16,17]. This is a crucial aspect as it allows the deployment of a self-contained compact source weighing less than 15 kg overall, with a total power consumption of no more than 240 W, requiring no further connections beyond the electrical one, and producing a reasonably Gaussian collimated beam with no external optics [17].…”

Section: Beamshapementioning

confidence: 99%

“…In ref. [16] the M2 of a 2.5 THz laser was determined by measuring the beam profile scanning a Golay cell detector with a 0.4-mm diameter aperture in a plane orthogonal to the emission direction of the QCL at different positions in front and behind the position of the beam On the other side, as mentioned previously, double-metal waveguides allow the highest operating temperatures and also represent by far the best choice for frequencies below 2 THz. From an application point of view, though, such strong sub-wavelength waveguides radiate into the entire semi-sphere above the device, more similar to an antenna than to a conventional semiconductor ridge waveguide, and often present very irregular profiles.…”

Section: Beamshapementioning

confidence: 99%

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Quantum cascade laser: a compact, low cost, solid-state source for plasma diagnostics

2012

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Quantum cascade lasers (QCL) are unipolar injection lasers based on intersubband transitions in a modular semiconductor heterostructure. The first THz QCL, operating at 67 µm (4.3 THz), was demonstrated in 2002; the wavelength range now extends beyond 250 µm (1.2 THz) and is entering the sub-terahertz frequency range for devices operated in external magnetic field. Although a number of different quantum designs have been demonstrated, increasing the operating temperature remains a major challenge: the maximum temperature is still ∼195 K, and recently approached 225 K in high magnetic fields. Nevertheless, compact continuous wave systems operating within Sterling coolers already ensure ample portability and turn-key operation and QCLs represent then the THz solid-state radiation source that actually shows the best performance in terms of optical output power, which can reach more than 100 mW average, and linewidth, typically in the tens of kHz for single mode devices. THz QCLs have then a realistic chance to deeply impact technological applications such as process monitoring, security controls, and bio-medical diagnostics. They are ideally suited though for plasma polarimetry and interferometry, thanks to their high polarization selectivity, excellent stability and ruggedness, and ease of high-speed modulation. Their compact size and monolithic cavity arrangement allows placement in the very proximity of the plasma to be monitored, easing requirements of stability against vibrations etc. Furthermore, the long coherence lengths should be easily compatible with interferometric arms of even very different lengths, a geometry ideal for coupling to a plasma reactor. The possibility of direct current modulation at MHz if not GHz frequencies ensures then an excellent temporal resolution of the meaurements, and a large low-frequency noise rejection. New analysis schemes also become feasible, for instance employing two-color lasers, operating at the same time at two appropriately

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Section: Beamshapementioning

confidence: 99%

Section: Beamshapementioning

confidence: 99%

Quantum cascade laser: a compact, low cost, solid-state source for plasma diagnostics

2012

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“…In the free running mode, the observed low frequency fluctuations and drift in the lock-in signal are a result of the frequency noise of the laser due to external contributions mainly from the temperature variations of the cryocooler. The contribution of the cryocooler also induces amplitude instability, 15 reflected by the fluctuations of the HEB mixer current and of the IF output power. In the second operating mode when the frequency stabilization loop is enabled, the lock-in signal becomes well stabilized and is maintained at the set point of zero, which implies that the QCL frequency is fully stabilized.…”

Section: -mentioning

confidence: 99%

Frequency and amplitude stabilized terahertz quantum cascade laser as local oscillator

Ren

Hayton

Hovenier

et al. 2012

Applied Physics Letters

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We demonstrate an experimental scheme to simultaneously stabilize the frequency and amplitude of a 3.5 THz third-order distributed feedback quantum cascade laser as a local oscillator. The frequency stabilization has been realized using a methanol absorption line, a power detector, and a proportional-integral-derivative (PID) loop. The amplitude stabilization of the incident power has been achieved using a swing-arm voice coil actuator as a fast optical attenuator, using the direct detection output of a superconducting mixer in combination with a 2nd PID loop. Improved Allan variance times of the entire receiver, as well as the heterodyne molecular spectra, are demonstrated. A terahertz (THz) quantum cascade laser (QCL) is the most promising solid-state source as the local oscillator (LO) for a high resolution heterodyne receiver operating at frequencies above 2 THz and, in particular, for a multi-pixel array receiver because of its high output power (typically mW). 1,2 Among different types of applications, a super-THz heterodyne receiver plays a vital role in astronomical observations, for instance to map a large number of fine structures and molecular lines associated with the formation of stars and planets in the Milky Way and nearby galaxies. 3 Those spectral lines at high frequencies are typically narrow ( a few MHz). Furthermore, the signals are, in general, very weak and deeply embedded within the noise. 3 The narrow spectral lines require either frequency or phase stabilization of a local oscillator. Since the intrinsic linewidth of a THz QCL is much narrower (

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“…Owing to the reduced overlap of the waveguide mode with doped semiconductor and metallic layers, the SP waveguide exhibits lower waveguide losses compared to MM waveguides. More significantly, though, is the far superior beam quality and lower beam divergence demonstrated [38]. The majority of THz QCLbased systems developed to date have consequently employed the SP waveguide .…”

Section: Introductionmentioning

confidence: 99%

Resonant-phonon depopulation terahertz quantum cascade lasers and their application in spectroscopic imaging

Dean¹,

Salih²,

Khanna³

et al. 2012

Semicond. Sci. Technol.

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The terahertz (THz) frequency quantum cascade laser (QCL) is a semiconductor heterostructure laser that has attracted much research interest over the past decade. We report on the high performance of THz QCLs based on a three-well resonant-phonon (RP) depopulation active region (AR) and operating in the frequency range 2.7 THz to 4.0 THz. Devices, processed into surface-plasmon waveguides, lased up to 116 K in pulsed mode with threshold current densities as low as 840 Acm -2 . The effects of the design frequency and laser cavity length on performance are discussed. We also report on the operation of QCLs with reduced AR thicknesses, and show, for the first time, that the AR thickness of RP QCLs processed in a surface plasmon waveguide can be reduced to as little as 5 m. Finally, we demonstrate the use of an electrically tuneable THz QCL, based on a heterogeneous AR, for spectroscopic imaging of the high-explosive pentaerythritol tetranitrate.

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Terahertz heterodyne receiver with quantum cascade laser and hot electron bolometer mixer in a pulse tube cooler

Cited by 71 publications

References 19 publications

Quantum cascade laser: a compact, low cost, solid-state source for plasma diagnostics

Quantum cascade laser: a compact, low cost, solid-state source for plasma diagnostics

Frequency and amplitude stabilized terahertz quantum cascade laser as local oscillator

Resonant-phonon depopulation terahertz quantum cascade lasers and their application in spectroscopic imaging

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