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Kumar, Sushil; Chan, Chun Wang I.; Hu, Qing; Reno, John L. |
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A 1.8-THz quantum cascade laser operating significantly above the temperature of hw/k |
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2011 |
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Nature Physics |
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7 |
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166-171 |
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QCL, 2 mW at 155 K and 1.8 THz |
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Several competing technologies continue to advance the field of terahertz science; of particular importance has been the development of a terahertz semiconductor quantum cascade laser (QCL), which is arguably the only solid-state terahertz source with average optical power levels of much greater than a milliwatt. Terahertz QCLs are required to be cryogenically cooled and improvement of their temperature performance is the single most important research goal in the field. Thus far, their maximum operating temperature has been empirically limited to ~planckω/kB, a largely inexplicable trend that has bred speculation that a room-temperature terahertz QCL may not be possible in materials used at present. Here, we argue that this behaviour is an indirect consequence of the resonant-tunnelling injection mechanism employed in all previously reported terahertz QCLs. We demonstrate a new scattering-assisted injection scheme to surpass this limit for a 1.8-THz QCL that operates up to ~1.9planckω/kB (163 K). Peak optical power in excess of 2 mW was detected from the laser at 155 K. This development should make QCL technology attractive for applications below 2 THz, and initiate new design strategies for realizing a room-temperature terahertz semiconductor laser. |
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631 |
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Манова, Н.Н.; Корнеева, Ю.П.; Корнеев, А.А.; Слыш, В.; Воронов, Б.М.; Гольцман, Г.Н. |
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Сверхпроводниковый NbN однофотонный детектор, интегрированный с четвертьволновым резонатором |
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2011 |
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Письма в Журнал технической физики |
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ПЖТФ |
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37 |
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10 |
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7 |
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SSPD |
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Исследована спектральная зависимость квантовой эффективности сверхпроводниковых NbN однофотонных детекторов, интегрированных с оптическими четвертьволновыми резонаторами с использованием диэлектриков Si3N4, SiO2, SiO. |
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RPLAB @ gujma @ |
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637 |
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Tretyakov, Ivan; Ryabchun, Sergey; Finkel, Matvey; Maslennikova, Anna; Kaurova, Natalia; Lobastova, Anastasia; Voronov, Boris; Gol'tsman, Gregory |
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Low noise and wide bandwidth of NbN hot-electron bolometer mixers |
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2011 |
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Appl. Phys. Lett. |
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Appl. Phys. Lett. |
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98 |
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033507 (1 to 3) |
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NbN HEB mixer |
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We report a record double sideband noise temperature of 600 K (5hν/kB) offered by a NbN hot-electron bolometer receiver at 2.5 THz. Allowing for standing wave effects, this value was found to be constant in the intermediate frequency range 1–7 GHz, which indicates that the mixer has an unprecedentedly large noise bandwidth in excess of 7 GHz. The insight into this is provided by gain bandwidth measurements performed at the superconducting transition. They show that the dependence of the bandwidth on the mixer length follows the model for an HEB mixer with diffusion and phonon cooling of the hot electrons. |
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RPLAB @ gujma @ |
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638 |
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Beck, M.; Klammer, M.; Lang, S.; Leiderer, P.; Kabanov, V. V.; Gol'tsman, G. N.; Demsar, J. |
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Energy-gap dynamics of superconducting NbN thin films studied by time-resolved terahertz spectroscopy |
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2011 |
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Phys. Rev. Lett. |
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Phys. Rev. Lett. |
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107 |
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17 |
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4 |
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NbN thin film, energy gap dynamics |
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Using time-domain terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare quasiparticle recombination rate, the Cooper pair-breaking rate and the electron-phonon coupling constant, λ=1.1±0.1, which is in excellent agreement with theoretical estimates. |
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RPLAB @ gujma @ |
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641 |
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Korneeva, Y.; Florya, I.; Semenov, A.; Korneev, A.; Goltsman, G. |
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New generation of nanowire NbN superconducting single-photon detector for mid-infrared |
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2011 |
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IEEE Trans. Appl. Supercond. |
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IEEE Trans. Appl. Supercond. |
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21 |
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3 |
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323-326 |
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SSPD |
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We present a break-through approach to mid-infrared single-photon detection based on nanowire NbN superconducting single-photon detectors (SSPD). Although SSPD became a mature technology for telecom wavelengths (1.3-1.55 μm) its further expansion to mid-infrared wavelength was hampered by low sensitivity above 2 μm. We managed to overcome this limit by reducing the nanowire width to 50 nm, while retaining high superconducting properties and connecting the wires in parallel to produce a voltage response of sufficient magnitude. The new device exhibits 10 times better quantum efficiency at 3.5 μm wavelength than the “standard” SSPD. |
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644 |
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