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Author (up) Il'in, K. S.; Cherednichenko, S. I.; Gol'tsman, G. N.; Currie, M.; Sobolewski, R. url  openurl
  Title Comparative study of the bandwidth of phonon-cooled NbN hot-electron bolometers in submillimeter and optical wavelength ranges Type Conference Article
  Year 1998 Publication Proc. 9th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 9th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 323-330  
  Keywords NbN HEB mixers  
  Abstract We report the results of the bandwidth measurements of NbN hot-electron bolometers, perfomied in the terahertz frequency domain at 140 GHz and 660 GHz and in time domain in the optical range at the wavelength of 395 nm.. Our studies were done on 3.5-nm-thick NbN films evaporated on sapphire substrates and patterned into ilin-size microbridges. In order to measure the gain bandwidth, we used two identical BWOs (140 or 660 GHz), one functioning as a local oscillator and the other as a signal source. The bandwidth we achieved was 3.5-4 GHz at 4.2 K with the optimal LO and DC biases. Time-domain measurements with a resolution below 300 fs were performed using an electro-optic sampling system, in the temperature range between 4.2 K to 9 K at various values of the bias current and optical power. The obtained response time of the NbN hot-electron bolometer to —100- fs-wide Ti:sapphire laser pulses was about 27 ps, what corresponds to the 5.9 GHz gain bandwidth.  
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  Notes Approved no  
  Call Number Serial 1590  
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Author (up) Il'in, K. S.; Currie, M.; Lindgren, M.; Milostnaya, I. I.; Verevkin, A. A.; Gol'tsman, G. N.; Sobolewski, R. url  doi
openurl 
  Title Quantum efficiency and time-domain response of superconducting NbN hot-electron photodetectors Type Journal Article
  Year 1999 Publication IEEE Trans. Appl. Supercond. Abbreviated Journal IEEE Trans. Appl. Supercond.  
  Volume 9 Issue 2 Pages 3338-3341  
  Keywords NbN SSPD, SNSPD  
  Abstract We report our studies on the response of ultrathin superconducting NbN hot-electron photodetectors. We have measured the photoresponse of few-nm-thick, micron-size structures, which consisted of single and multiple microbridges, to radiation from the continuous-wave semiconductor laser and the femtosecond Ti:sapphire laser with the wavelength of 790 nm and 400 nm, respectively. The maximum responsivity was observed near the film's superconducting transition with the device optimally current-biased in the resistive state. The responsivity of the detector, normalized to its illuminated area and the coupling factor, was 220 A/W(3/spl times/10/sup 4/ V/W), which corresponded to a quantum efficiency of 340. The responsivity was wavelength independent from the far infrared to the ultraviolet range, and was at least two orders of magnitude higher than comparable semiconductor optical detectors. The time constant of the photoresponse signal was 45 ps, when was measured at 2.15 K in the resistive (switched) state using a cryogenic electro-optical sampling technique with subpicosecond resolution. The obtained results agree very well with our calculations performed using a two-temperature model of the electron heating in thin superconducting films.  
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  ISSN 1051-8223 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1566  
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Author (up) Il'in, K. S.; Verevkin, A. A.; Gol'tsman, G. N.; Sobolewski, R. url  doi
openurl 
  Title Infrared hot-electron NbN superconducting photodetectors for imaging applications Type Journal Article
  Year 1999 Publication Supercond. Sci. Technol. Abbreviated Journal Supercond. Sci. Technol.  
  Volume 12 Issue 11 Pages 755-758  
  Keywords NbN SSPD, SNSPD  
  Abstract We report an effective quantum efficiency of 340, responsivity >200 A W-1 (>104 V W-1) and response time of 27±5 ps at temperatures close to the superconducting transition for NbN superconducting hot-electron photodetectors (HEPs) in the near-infrared and optical ranges. Our studies were performed on a few nm thick NbN films deposited on sapphire substrates and patterned into µm-size multibridge detector structures, incorporated into a coplanar transmission line. The time-resolved photoresponse was studied by means of subpicosecond electro-optic sampling with 100 fs wide laser pulses. The quantum efficiency and responsivity studies of our photodetectors were conducted using an amplitude-modulated infrared beam, fibre-optically coupled to the device. The observed picosecond response time and the very high efficiency and sensitivity of the NbN HEPs make them an excellent choice for infrared imaging photodetectors and input optical-to-electrical transducers for superconducting digital circuits.  
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  ISSN 0953-2048 ISBN Medium  
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  Notes Approved no  
  Call Number Serial 1562  
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Author (up) Il’in, K. S.; Milostnaya, I. I.; Verevkin, A. A.; Gol’tsman, G. N.; Gershenzon, E. M.; Sobolewski, R. url  doi
openurl 
  Title Ultimate quantum efficiency of a superconducting hot-electron photodetector Type Journal Article
  Year 1998 Publication Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.  
  Volume 73 Issue 26 Pages 3938-3940  
  Keywords NbN SSPD, SNSPD  
  Abstract The quantum efficiency and current and voltage responsivities of fast hot-electron photodetectors, fabricated from superconducting NbN thin films and biased in the resistive state, have been shown to reach values of 340, 220 A/W, and 4×104 V/W,

respectively, for infrared radiation with a wavelength of 0.79 μm. The characteristics of the photodetectors are presented within the general model, based on relaxation processes in the nonequilibrium electron heating of a superconducting thin film. The observed, very high efficiency and sensitivity of the superconductor absorbing the photon are explained by the high multiplication rate of quasiparticles during the avalanche breaking of Cooper pairs.
 
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  ISSN 0003-6951 ISBN Medium  
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  Notes Approved no  
  Call Number Serial 1579  
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Author (up) Jukna, A.; Kitaygorsky, J.; Pan, D.; Cross, A.; Perlman, A.; Komissarov, I.; Sobolewski, R.; Okunev, O.; Smirnov, K.; Korneev, A.; Chulkova, G.; Milostnaya, I.; Voronov, B.; Gol'tsman, G. doi  openurl
  Title Dynamics of hotspot formation in nanostructured superconducting stripes excited with single photons Type Journal Article
  Year 2008 Publication Acta Physica Polonica A Abbreviated Journal Acta Physica Polonica A  
  Volume 113 Issue 3 Pages 955-958  
  Keywords SSPD, SNSPD  
  Abstract Dynamics of a resistive hotspot formation by near-infrared-wavelength single photons in nanowire-type superconducting NbN stripes was investigated. Numerical simulations of ultrafast thermalization of photon-excited nonequilibrium quasiparticles, their multiplication and out-diffusion from a site of the photon absorption demonstrate that 1.55 μm wavelength photons create in an ultrathin, two-dimensional superconducting film a resistive hotspot with the diameter which depends on the photon energy, and the nanowire temperature and biasing conditions. Our hotspot model indicates that under the subcritical current bias of the 2D stripe, the electric field penetrates the superconductor at the hotspot boundary, leading to suppression of the stripe superconducting properties and accelerated development of a voltage transient across the stripe.  
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  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1414  
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