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| Author |
Tong, C. Edward; Trifonov, Andrey; Blundell, Raymond; Shurakov, Alexander; Gol’tsman, Gregory |
| Title |
A digital terahertz power meter based on an NbN thin film |
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Abstract |
| Year |
2014 |
Publication |
Proc. 25th Int. Symp. Space Terahertz Technol. |
Abbreviated Journal |
Proc. 25th Int. Symp. Space Terahertz Technol. |
| Volume |
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Pages |
170 |
| Keywords |
waveguide NbN HEB mixers |
| Abstract |
We have further studied the effect of subjecting a superconducting Hot Electron Bolometer (HEB) element made from an NbN thin film to microwave radiation. Since the photon energy is weak, the microwave radiation does not simply heat the film, but generates a bi-static state, switching between the superconducting and normal states, upon the application of a small voltage bias. Indeed, a relaxation oscillation of a few MHz has previously been reported in this regime [1]. Switching between the superconducting and normal states modulates the reflected microwave pump power from the device. A simple homodyne setup readily recovers the spontaneous switching waveform in the time domain. The switching frequency is a function of both the bias voltage (DC heating) and the applied microwave power. In this work, we use a 0.8 THz HEB waveguide mixer for the purpose of demonstration. The applied microwave pump, coupled through a directional coupler, is at 1 GHz. Since the pump power is of the order of a few μW, a room temperature amplifier is sufficient to amplify the reflected pump power from the HEB mixer, which beats with the microwave source in a homodyne set-up. After further amplification, the switching waveform is passed onto a frequency counter. The typical frequency of the switching pulses is 3-5 MHz. It is found that the digital frequency count increases with higher microwave pump power. When the HEB mixer is subjected to additional optical power at 0.8 THz, the frequency count also increases. When we vary the incident optical power by using a wire grid attenuator, a linear relationship is observed between the frequency count and the applied optical power, over at least an order of magnitude of power. This phenomenon can be exploited to develop a digital power meter, using a very simple electronics setup. Further experiments are under way to determine the range of linearity and the accuracy of calibration transfer from the microwave to the THz regime. References 1. Y. Zhuang, and S. Yngvesson, “Detection and interpretation of bistatic effects in NbN HEB devices,” Proc. 13 th Int. Symp. Space THz Tech., 2002, pp. 463–472. |
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1366 |
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Beck, Matthias; Leiderer, Paul; Kabanov, Viktor V.; Gol'tsman, Gregory; Helm, Manfred; Demsar, Jure |
| Title |
Energy-gap dynamics of a superconductor NbN studied by time-resolved terahertz spectroscopy |
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Abstract |
| Year |
2012 |
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INIS |
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INIS |
| Volume |
45 |
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12 |
Pages |
1-3 |
| Keywords |
NbN energy gap |
| Abstract |
Using time-resolved terahertz (THz) spectroscopy we performed direct studies of the photoinduced suppression and recovery of the SC gap in a conventional SC 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 important microscopic constants: the Cooper pair-breaking rate via phonon absorption and the bare quasiparticle recombination rate. From the latter we were able to extract the dimensionless electron-phonon coupling constant, λ=1.1±0.1, in excellent agreement with theoretical estimates. The technique also allowed us to determine the absorbed energy required to suppress SC, which in NbN equals the thermodynamic condensation energy (in cuprates the two differ by an order of magnitude). Finally, we present the first studies of dynamics following resonant excitation with intense narrow band THz pulses tuned to above and below the superconducting gap. These suggest an additional process, particularly pronounced near Tc, that could be attributed to amplification of SC via effective quasiparticle cooling. |
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1383 |
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Pentin, I. V.; Smirnov, A. V.; Ryabchun, S. A.; Gol’tsman, G. N.; Vaks, V. L.; Pripolzin, S. I.; Paveliev, D. G. |
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Heterodyne source of THz range based on semiconductor superlattice multiplier |
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Conference Article |
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2011 |
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IRMMW-THz |
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IRMMW-THz |
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1-2 |
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NbN HEB mixer, superlattice |
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We present the results of our studies of the possibility of developing a heterodyne receiver incorporating a hot-electron bolometer mixer as the detector and a semiconductor superlattice multiplier driven by a reference synthesizer as the local oscillator. We observe that such a local oscillator offers enough power in the terahertz range to pump the HEB into the operating state. |
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6105209 |
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1384 |
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Ryabchun, S.; Smirnov, A.; Pentin, I.; Vakhtomin, Yu.; Smirnov, K.; Kaurova, N.; Voronov, B.; Goltsman, G. |
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Superconducting single photon detector integrated with optical cavity |
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Conference Article |
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2011 |
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Proc. MLPLIT |
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Proc. MLPLIT |
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143-145 |
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NbN SSPD, cavity |
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Suzdal / Vladimir (Russia) |
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Modern laser physics and laser-information technologies for science and manufacture |
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1st international russian-chinese conference / youthschool-workshop |
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September 23-28, 2011 |
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1385 |
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Maslennikova, A.; Larionov, P.; Ryabchun, S.; Smirnov, A.; Pentin, I.; Vakhtomin, Yu.; Smirnov, K.; Kaurova, N.; Voronov, B.; Goltsman, G. |
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Noise equivalent power and dynamic range of NBN hot-electron bolometers |
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Conference Article |
| Year |
2011 |
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Proc. MLPLIT |
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Proc. MLPLIT |
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146-148 |
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NbN HEB |
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Suzdal / Vladimir (Russia) |
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Modern laser physics and laser-information technologies for science and manufacture |
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1st international russian-chinese conference / youthschool-workshop |
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September 23-28, 2011 |
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1386 |
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