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Richter H, Semenov A, Hubers H-W, Smirnov K, Gol’tsman G, Voronov B. Phonon cooled hot-electron bolometric mixer for 1-5 THz. In: Proc. 29th IRMMW / 12th THz.; 2004. p. 241–2.
Abstract: Heterodyne receivers for applications in astronomy and planetary research need quantum limited sensitivity. In instruments which are currently built for SOFIA and Herschel, superconducting hot electron bolometers (HEB) are used to achieve this goal at frequencies above 1.4 THz. In order to optimize the performance for this frequency of hot electron bolometer mixers with different in-plane dimensions and logarithmic-spiral feed antennas have been investigated. Their noise temperatures and beam patterns were measured. Above 3 THz the best performance was achieved with a superconducting bridge of 2.0/spl times/0.2 /spl mu/m/sup 2/ incorporated in a logarithmic spiral antenna. The DSB noise temperatures were 2700 K, 4700 and 6400 K at 3.1 THz, 4.3 THz and 5.2 THz, respectively. The results demonstrate that the NbN HEB is very well suited as a mixer for THz heterodyne receivers up to at least 5 THz.
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Rubtsova I, Korneev A, Matvienko V, Chulkova G, Milostnaya I, Goltsman G, et al. Spectral sensitivity, quantum efficiency, and noise equivalent power of NbN superconducting single-photon detectors in the IR range. In: Proc. 29th IRMMW / 12th THz.; 2004. p. 461–2.
Abstract: We have developed nanostructured NbN superconducting single-photon detectors capable of GHz-rate photon counting in the 0.4 to 5 /spl mu/m wavelength range. Quantum efficiency of 30%, dark count rate 3/spl times/10/sup -4/ s/sup -1/, and NEP=10/sup -20/ W/Hz/sup -1/2/ have been measured at the 1.3-/spl mu/m wavelength for the device operating at 2.0 K.
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Baselmans JJA, Hajenius M, Gao J, de Korte P, Klapwijk TM, Voronov B, et al. Doubling of sensitivity and bandwidth in phonon-cooled hot-electron bolometer mixers. In: Zmuidzinas J, Holland WS, Withington S, editors. Proc. SPIE. Vol 5498. SPIE; 2004. p. 168–76.
Abstract: NbN hot electron bolometer (HEB) mixers are at this moment the best heterodyne detectors for frequencies above 1 THz. However, the fabrication procedure of these devices is such that the quality of the interface between the NbN superconducting film and the contact structure is not under good control. This results in a contact resistance between the NbN bolometer and the contact pad. We compare identical bolometers, with different NbN – contact pad interfaces, coupled with a spiral antenna. We find that cleaning the NbN interface and adding a thin additional superconductor prior to the gold contact deposition improves the noise temperature and the bandwidth of the HEB mixers with more than a factor of 2. We obtain a DSB noise temperature of 950 K at 2.5 THz and a Gain bandwidth of 5-6 GHz. For use in real receiver systems we design small volume (0.15x1 micron) HEB mixers with a twin slot antenna. We find that these mixers combine good sensitivity (900 K at 1.6 THz) with low LO power requirement, which is 160 – 240 nW at the Si lens of the mixer. This value is larger than expected from the isothermal technique and the known losses in the lens by a factor of 3-3.5.
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Hajenius M, Baselmans JJA, Gao JR, Klapwijk TM, de Korte PAJ, Voronov B, et al. Low noise NbN superconducting hot electron bolometer mixers at 1.9 and 2.5 THz. Supercond Sci Technol. 2004;17(5):S224–S228.
Abstract: NbN phonon-cooled hot electron bolometer mixers (HEBs) have been realized with negligible contact resistance between the bolometer itself and the contact structure. Using a combination of in situ cleaning of the NbN film and the use of an additional superconducting interlayer of a 10 nm NbTiN layer between the Au of the contact structure and the NbN film superior noise temperatures have been obtained as low as 950 K at 2.5 THz and 750 K at 1.9 THz. Here we address in detail the DC characterization of these devices, the interface transparencies between the bolometers and the contacts and the consequences of these factors on the mixer performance.
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Martin슠Harwit. The Herschel mission. Advances in Space Research. 2004;34(3):568–72.
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Semenov A, Richter H, Smirnov K, Voronov B, Gol'tsman G, Hübers H-W. The development of terahertz superconducting hot-electron bolometric mixers. Supercond Sci Technol. 2004;17(5):436–9.
Abstract: We present recent advances in the development of NbN hot-electron bolometric (HEB) mixers for flying terahertz heterodyne receivers. Three important issues have been addressed: the quality of the source NbN films, the effect of the bolometer size on the spectral properties of different planar feed antennas, and the local oscillator (LO) power required for optimal operation of the mixer. Studies of the NbN films with an atomic force microscope indicated a surface structure that may affect the performance of the smallest mixers. Measured spectral gain and noise temperature suggest that at frequencies above 2.5 THz the spiral feed provides better overall performance than the double-slot feed. Direct measurements of the optimal LO power support earlier estimates made in the framework of the uniform mixer model.
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Baselmans JJA, Hajenius M, Gao JR, Klapwijk TM, de Korte PAJ, Voronov B, et al. Doubling of sensitivity and bandwidth in phonon cooled hot electron bolometer mixers. Appl Phys Lett. 2004;84(11):1958–60.
Abstract: We demonstrate that the performance of NbN lattice cooled hot electron bolometer mixers depends strongly on the interface quality between the bolometer and the contact structure. We show experimentally that both the receiver noise temperature and the gain bandwidth can be improved by more than a factor of 2 by cleaning the interface and adding an additional superconducting interlayer to the contact pad. Using this we obtain a double sideband receiver noise temperature TN,DSB=950 K
at 2.5 THz and 4.3 K, uncorrected for losses in the optics. At the same bias point, we obtain an IF gain bandwidth of 6 GHz.
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Yu B, Zeng F, Yang Y, Xing Q, Chechin A, Xin X, et al. Torsional vibrational modes of tryptophan studied by terahertz time-domain spectroscopy. Biophys. J.. 2004;86(3):1649–54.
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Ciulin V, Carter SG, Sherwin MS. Terahertz optical mixing in biased GaAs single quantum wells. Phys Rev B. 2004;70(11):115312–(1.
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Korneev A, Kouminov P, Matvienko V, Chulkova G, Smirnov K, Voronov B, et al. Sensitivity and gigahertz counting performance of NbN superconducting single-photon detectors. Appl Phys Lett. 2004;84(26):5338–40.
Abstract: We have measured the quantum efficiencysQEd, GHz counting rate, jitter, and noise-equivalentpowersNEPdof nanostructured NbN superconducting single-photon detectorssSSPDsdin thevisible to infrared radiation range. Our 3.5-nm-thick and 100- to 200-nm-wide meander-typedevices(total area 10310mm2), operating at 4.2 K, exhibit an experimental QE of up to 20% inthe visible range and,10% at 1.3 to 1.55mm wavelength and are potentially sensitive up tomidinfrareds,10mmdradiation. The SSPD counting rate was measured to be above 2 GHz withjitter,18 ps, independent of the wavelength. The devices’ NEP varies from,10−17W/Hz1/2for1.55mm photons to,10−20W/Hz1/2for visible radiation. Lowering the SSPD operatingtemperature to 2.3 K significantly enhanced its performance, by increasing the QE to,20% andlowering the NEP level to,3310−22W/Hz1/2, both measured at 1.26mm wavelength.
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