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Schwaab, G. W.; Hübers, H.-W.; Schubert, J.; Erichsen, Patrik; Gol'tsman, G.; Semenov, A.; Verevkin, A.; Cherednichenko, S.; Gershenzon, E. |
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A high resolution spectrometer for the investigation of molecular structures in the THZ range |
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1999 |
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Proc. 10th Int. Symp. Space Terahertz Technol. |
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Proc. 10th Int. Symp. Space Terahertz Technol. |
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530-538 |
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antireflection coatings, dielectric mirrors |
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A status report on the design study of a novel tunable far-infrared (TuFTR) spectrometer for the investigation of the structure of weakly bound molecular complexes is given. The goal is a sensitive TuFIR spectrometer with full frequency coverage from 1-6 THz. To hit the goal, advanced sources (e.g. p-Ge lasers) and detectors (e.g. superconducting hot electron bolometric (HEB) mixers) shall be employed to extend the technique of cavity ringdown spectroscopy, that is currently used at optical and infrared frequencies to the FIR spectral range. Critical for such a system are high-Q resonators that still allow good optical coupling, and wideband antireflection coatings to increase detector sensitivity and decrease optical path losses. 2 nd order effective media theory and an iterative multilayer algorithm have been employed to design wideband antireflection coatings for dielectrics with large dielectric constants like Ge or Si. Taking into account 6 layers, for Si bandwidths of 100% of the center frequency could be obtained with power reflectivities below 1% for both polarizations simultaneously. Wideband dielectric mirrors including absorption losses were also studied yielding a bandwidth of about 50% with reflectivities larger than 99.5%. |
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1577 |
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Schubert, J.; Semenov, A.; Hübers, H.-W.; Gol'tsman, G.; Schwaab, G.; Voronov, B.; Gershenzon, E. |
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Broad-band terahertz NbN hot-electron bolometric mixer |
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1999 |
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Inst. Phys. Conf. |
Abbreviated Journal |
Inst. Phys. Conf. |
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167 |
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663-666 |
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NbN HEB mixers |
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4th Europ. Conf. on Appl. Superconductivity, Barcelona, Spain, 14-17 September 1999 |
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1578 |
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Lindgren, M.; Currie, M.; Zeng, W.-S.; Sobolewski, R.; Cherednichenko, S.; Voronov, B.; Gol'tsman, G. N. |
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Picosecond response of a superconducting hot-electron NbN photodetector |
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1998 |
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Appl. Supercond. |
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Appl. Supercond. |
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6 |
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7-9 |
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423-428 |
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NbN SSPD, SNSPD |
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The ps optical response of ultrathin NbN photodetectors has been studied by electro-optic sampling. The detectors were fabricated by patterning ultrathin (3.5 nm thick) NbN films deposited on sapphire by reactive magnetron sputtering into either a 5×10 μm2 microbridge or 25 1 μm wide, 5 μm long strips connected in parallel. Both structures were placed at the center of a 4 mm long coplanar waveguide covered with Ti/Au. The photoresponse was studied at temperatures ranging from 2.15 K to 10 K, with the samples biased in the resistive (switched) state and illuminated with 100 fs wide laser pulses at 395 nm wavelength. At T=2.15 K, we obtained an approximately 100 ps wide transient, which corresponds to a NbN detector response time of 45 ps. The photoresponse can be attributed to the nonequilibrium electron heating effect, where the incident radiation increases the temperature of the electron subsystem, while the phonons act as the heat sink. The high-speed response of NbN devices makes them an excellent choice for an optoelectronic interface for superconducting digital circuits, as well as mixers for the terahertz regime. The multiple-strip detector showed a linear dependence on input optical power and a responsivity =3.9 V/W. |
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0964-1807 |
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1584 |
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Svechnikov, S.; Verevkin, A.; Voronov, B.; Menschikov, E.; Gershenzon, E.; Gol'tsman, G. |
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Quasioptical phonon-cooled NbN hot electron bolometer mixers at 0.5-1.1 THz |
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1998 |
Publication |
Proc. 9th Int. Symp. Space Terahertz Technol. |
Abbreviated Journal |
Proc. 9th Int. Symp. Space Terahertz Technol. |
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45-51 |
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NbN HEB mixers |
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The noise performance of a receiver incorporating spiral antenna coupled NbN phonon-cooled superconducting hot electron bolometric mixer is measured from 450 GHz to 1200 GHz. The mixer element is thin (thickness nm) NbN 1.5 pm wide and 0.2 i.um long film fabricated by lift-off e-beam lithography on high-resistive silicon substrate. The noise of the receiver temperature is 1000 K at 800-900 GHz, 1200 K at 950 GHz, and 1600 K at 1.08 THz. The required (absorbed) local-oscillator power is —20 nW. |
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1586 |
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Gousev, Yu. P.; Olsson, H. K.; Gol'tsman, G. N.; Voronov, B. M.; Gershenzon, E. M. |
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NbN hot-electron mixer at radiation frequencies between 0.9 THz and 1.2 THz |
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1998 |
Publication |
Proc. 9th Int. Symp. Space Terahertz Technol. |
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Proc. 9th Int. Symp. Space Terahertz Technol. |
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121-129 |
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NbN HEB mixers |
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We report on noise temperature measurements for a NbN phonon-cooled hot-electron mixer at radiation frequencies between 0.9 THz and 1.2 THz. Radiation was coupled to the mixer, placed in a vacuum chamber of He cryostat, by means of a planar spiral antenna and a Si immersion lens. A backward-wave oscillator, tunable throughout the spectral range, delivered an output power of few 1.1W that was enough for optimum operation of the mixer. At 4.2 K ambient temperature and 1.025 THz radiation frequency, we obtained a receiver noise temperature of 1550 K despite of using a relatively noisy room-temperature amplifier at the intermediate frequency port. The noise temperature was fairly constant throughout the entire operation range and for intermediate frequencies from 1 GHz to 2 GHz. |
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1588 |
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