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Kroug, M., Cherednichenko, S., Choumas, M., Merkel, H., Kollberg, E., Hübers, H. - W., et al. (2001). HEB quasi-optical heterodyne receiver for THz frequencies. In Proc. 12th Int. Symp. Space Terahertz Technol. (pp. 244–252). San Diego, CA, USA.
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Kroug, M., Cherednichenko, S., Merkel, H., Kollberg, E., Voronov, B., Gol'tsman, G., et al. (2001). NbN hot electron bolometric mixers for terahertz receivers. IEEE Trans. Appl. Supercond., 11(1), 962–965.
Abstract: Sensitivity and gain bandwidth measurements of phonon-cooled NbN superconducting hot-electron bolometer mixers are presented. The best receiver noise temperatures are: 700 K at 1.6 THz and 1100 K at 2.5 THz. Parylene as an antireflection coating on silicon has been investigated and used in the optics of the receiver. The dependence of the mixer gain bandwidth (GBW) on the bias voltage has been measured. Starting from low bias voltages, close to operating conditions yielding the lowest noise temperature, the GBW increases towards higher bias voltages, up to three times the initial value. The highest measured GBW is 9 GHz within the same bias range the noise temperature increases by a factor of two.
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Kroug, M., Yagoubov, P., Gol'tsman, G., & Kollberg, E. (1997). NbN quasioptical phonon cooled hot electron bolometric mixers at THz frequencies. In Inst. Phys. Conf. Ser. (Vol. 1, pp. 405–408). Bristol.
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Lang, P. T., Knott, W. J., Leipold, I., Renk, K. F., Semenov, A. D., & Gol'tsman, G. N. (1992). Generation and detection of tunable ultrashort infrared and far-infrared radiation pulses of high intensity. Int. J. of Infrared and Millimeter Waves, 13(3), 373–380.
Abstract: We report on generation and detection of intense pulsed radiation with frequency tunability in the infrared and far-infrared spectral regions. Infrared radiation is generated with a transversally electrically excited high pressure CO2 laser. A laser pulse of a total duration of about 300 ns consisted, due to self mode locking, of a series of single pulses, some with pulse durations of less than 450 ps and peak powers larger than 20 MW. Using these pulses for optical with durations less than 400 ps were obtained. For detection a new ultrafast superconducting detector was used.
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Lang, P. T., Leipold, I., Knott, W. J., Semenov, A. D., Gol'tsman, G. N., & Renk, K. F. (1991). New far-infrared laser lines from CH3Cl and CH3Br optically pumped with a continuously tunable high pressure CO2 laser. Appl. Phys. B, 53(4), 207–212.
Abstract: In this paper we report on the detection of new far-infrared laser lines from CH3Cl and CH3Br optically pumped with a continuously tunable high pressure CO2 laser. We found 80 new lines for CH3Cl and 9 new lines for CH3Br in the frequency region between 16 cm−1 and 41 cm−1, all due to stimulated Raman scattering. For the Raman gain regions bandwidths up to about 700 MHz were found. We also observed high intensity short far-infrared laser pulses of durations in the nanosecond regime.
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Lindgren, M., Currie, M., Zeng, W. - S., Sobolewski, R., Cherednichenko, S., Voronov, B., et al. (1998). Picosecond response of a superconducting hot-electron NbN photodetector. Appl. Supercond., 6(7-9), 423–428.
Abstract: 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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Lindgren, M., Zorin, M. A., Trifonov, V., Danerud, M., Winkler, D., Karasik, B. S., et al. (1994). Optical mixing in a patterned YBa2Cu3O7-δ thin film. Appl. Phys. Lett., 65(26), 3398–3400.
Abstract: Mixing of 1.56 µm infrared radiation from two lasers in a high quality YBa2Cu3O7-δ thin film, patterned to parallel strips, was demonstrated. A mixer bandwidth of 18 GHz, limited by the measurement system, was obtained. A model based on nonequilibrium electron heating gives a good fit to the data and predicts an intrinsic mixer bandwidth in excess of 100 GHz, operating in the whole infrared spectrum. Reduction of bolometric effects and ways to decrease the conversion loss of the mixer is discussed. The minimum conversion loss is expected to be ~10 dB.
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Lipatov, A., Okunev, O., Smirnov, K., Chulkova, G., Korneev, A., Kouminov, P., et al. (2002). An ultrafast NbN hot-electron single-photon detector for electronic applications. Supercond. Sci. Technol., 15(12), 1689–1692.
Abstract: We present the latest generation of our superconducting single-photon detector (SPD), which can work from ultraviolet to mid-infrared optical radiation wavelengths. The detector combines a high speed of operation and low jitter with high quantum efficiency (QE) and very low dark count level. The technology enhancement allows us to produce ultrathin (3.5 nm thick) structures that demonstrate QE hundreds of times better, at 1.55 μm, than previous 10 nm thick SPDs. The best, 10 × 10 μm2, SPDs demonstrate QE up to 5% at 1.55 μm and up to 11% at 0.86 μm. The intrinsic detector QE, normalized to the film absorption coefficient, reaches 100% at bias currents above 0.9 Ic for photons with wavelengths shorter than 1.3 μm.
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Lobanov, Y. V., Tong, C. - Y. E., Hedden, A. S., Blundell, R., & Gol'tsman, G. N. (2010). Microwave-assisted슠measurement슠of the슠frequency슠response슠of슠terahertz슠HEB슠mixers슠with a슠fourier슠transform슠spectrometer. In 21st International Symposium on Space Terahertz Technology (pp. 420–423).
Abstract: We describe a novel method of operation of the HEB direct detector for use with a Fourier Transform Spectrometer. Instead of elevating the bath temperature, we have measured the RF response of waveguide HEB mixers by applying microwave radiation to select appropriate bias conditions. In our experiment, a microwave signal is injected into the HEB mixer via its IF port. By choosing an appropriate injection level, the device can be operated close to the desired operating point. Furthermore, we have shown that both thermal biasing and microwave injection can reproduce the same spectral response of the HEB mixer. However, with the use of microwave injection, there is no need to wait for the mixer to reach thermal equilibrium, so characterisation can be done in less time. Also, the liquid helium consumption for our wet cryostat is also reduced. We have demonstrated that the signalto-noise ratio of the FTS measurements can be improved with microwave injection.
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Lobanov, Y., Shcherbatenko, M., Finkel, M., Maslennikov, S., Semenov, A., Voronov, B. M., et al. (2015). NbN hot-electron-bolometer mixer for operation in the near-IR frequency range. IEEE Trans. Appl. Supercond., 25(3), 2300704 (1 to 4).
Abstract: Traditionally, hot-electron-bolometer (HEB) mixers are employed for THz and “super-THz” heterodyne detection. To explore the near-IR spectral range, we propose a fiber-coupled NbN film based HEB mixer. To enhance the incident-light absorption, a quasi-antenna consisting of a set of parallel stripes of gold is used. To study the antenna effect on the mixer performance, we have experimentally studied a set of devices with different size of the Au stripe and spacing between the neighboring stripes. With use of the well-known isotherm technique we have estimated the absorption efficiency of the mixer, and the maximum efficiency has been observed for devices with the smallest pitch of the alternating NbN and NbN-Au stripes. Also, a proper alignment of the incident Eâƒ<2014>-field with respect to the stripes allows us to improve the coupling further. Studying IV-characteristics of the mixer under differently-aligned Eâƒ<2014>-field of the incident radiation, we have noticed a difference in their shape. This observation suggests that a difference exists in the way the two waves with orthogonal polarizations parallel and perpendicular Eâƒ<2014>-field to the stripes heat the electrons in the HEB mixer. The latter results in a variation in the electron temperature distribution over the HEB device irradiated by the two waves.
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Lobanov, Y., Shcherbatenko, M., Semenov, A., Kovalyuk, V., Kahl, O., Ferrari, S., et al. (2017). Superconducting nanowire single photon detector for coherent detection of weak signals. IEEE Trans. Appl. Supercond., 27(4), 1–5.
Abstract: Traditional photon detectors are operated in the direct detection mode, counting incident photons with a known quantum efficiency. Here, we have investigated a superconducting nanowire single photon detector (SNSPD) operated as a photon counting mixer at telecommunication wavelength around 1.5 μm. This regime of operation combines excellent sensitivity of a photon counting detector with excellent spectral resolution given by the heterodyne technique. Advantageously, we have found that low local oscillator (LO) power of the order of hundreds of femtowatts to a few picowatts is sufficient for clear observation of the incident test signal with the sensitivity approaching the quantum limit. With further optimization, the required LO power could be significantly reduced, which is promising for many practical applications, such as the development of receiver matrices or recording ultralow signals at a level of less-than-one-photon per second. In addition to a traditional NbN-based SNSPD operated with normal incidence coupling, we also use detectors with a travelling wave geometry, where a NbN nanowire is placed on the top of a Si 3 N 4 nanophotonic waveguide. This approach is fully scalable and a large number of devices could be integrated on a single chip.
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Lobanov, Y., Tong, C., Blundell, R., & Gol'tsman, G. (2009). A study of direct detection effect on the linearity of hot electron bolometer mixers. In Proc. 20th Int. Symp. Space Terahertz Technol. (pp. 282–287).
Abstract: We have performed a study of how direct detection affects the linearity and hence the calibration of an HEB mixer. Two types of waveguide HEB devices have been used: a 0.8 THz HEB mixer and a 1.0 THz HEB mixer which is ~5 times smaller than the former. Two independent experimental approaches were used. In the ΔG/G method, the conversion gain of the HEB mixer is first measured as a function of the bias current for a number of bias voltages. At each bias setting, we carefully measure the change in the operating current when the input loads are switched. From the measured data, we can derive the expected difference in gain between the hot and cold loads. In the second method (injection method [1]), the linearity of the HEB mixer is independently measured by injecting a modulated signal for different input load temperatures. The results of both approaches confirm that there is gain compression in the operation of HEB mixers. Based on the results of our measurements, we discuss the impact of direct detection effects on the operation of HEB mixers.
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Lobanov, Y., Tong, E., Blundell, R., Hedden, A., Voronov, B., & Gol'tsman, G. (2011). Large-signal frequency response of an HEB mixer: from 300 MHz to terahertz. IEEE Trans. Appl. Supercond., 21(3), 628–631.
Abstract: We present a study of the large signal frequency response of an HEB mixer over a wide frequency range. In our experiments, we have subjected the HEB mixer to incident electromagnetic radiation from 0.3 GHz to 1 THz. The mixer element is an NbN film deposited on crystalline quartz. The mixer chip is mounted in a waveguide cavity, coupled to free space with a diagonal horn. At microwave frequencies, electromagnetic radiation is applied through the coaxial bias port of the mixer block. At higher frequencies the input signal passes via the diagonal horn feed. At each frequency, the incident power is varied and a family of I-V curves is recorded. From the curves we identify 3 distinct regimes of operation of the mixer separated by the phonon relaxation frequency and the superconducting energy gap frequency observed at about 3 GHz and 660 GHz respectively. In this paper, we will present observed curves and discuss the results of our experiment.
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Lobanov, Y. V., Tong, C. - Y. E., Hedden, A. S., Blundell, R., Voronov, B. M., & Gol'tsman, G. N. (2011). Direct measurement of the gain and noise bandwidths of HEB mixers. IEEE Trans. Appl. Supercond., 21(3), 645–648.
Abstract: The intermediate frequency (IF) bandwidth of a hot electron bolometer (HEB) mixer is an important parameter of the mixer, in that it helps to determine its suitability for a given application. With the availability of wideband low noise amplifiers, it is simple to measure the performance of an HEB mixer over a wide range of IF at a fixed LO frequency using the standard Y-factor method. This in-situ method allows us to measure both the gain and noise bandwidths simultaneously. We have also measured mixer output impedance with a vector network analyser. Intrinsic time constant has been extracted from the impedance data and compared to the mixer's bandwidths determined from receiver Y-factor measurement.
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Loudkov, D., Khosropanah, P., Cherednichenko, S., Adam, A., MerkeI, H., Kollberg, E., et al. (2002). Broadband fourier transform spectrometer (FTS) measurements of spiral and double-slot planar antennas at THz frequencies. In Proc. 13th Int. Symp. Space Terahertz Technol. (pp. 373–369).
Abstract: The direct responses of NbN phonon-cooled hot electron bolometer (HEB) mixers, integrated with different planar antennas, are measured, using Fourier Transform Spectrometer (F1S). One spiral antenna and several double slot antennas, designed for 0.6, 1.4, 1.6, 1.8 and 2.5 THz central frequencies, are investigated. The Optimization of the measurement set-up is discussed in terms of the beam splitter and the F11S-to-HEB coupling. The result shows that the spiral antenna is circular polarized and has a bandwidth of about 2 THz. The frequency bands of double slot antennas show some shift from the design values and their relative bandwidth increases by increasing the design frequency. The antenna responses do not depend on the HEB bias point and temperature, as long as the device is in the resistive state.
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