Ekstörm H, Kollberg E, Yagoubov P, Gol'tsman G, Gershenzon E, Yngvesson S. Gain and noise bandwidth of NbN hot-electron bolometric mixers. Appl Phys Lett. 1997;70(24):3296–8.
Abstract: We have measured the noise performance and gain bandwidth of 35 Å thin NbN hot-electron mixers integrated with spiral antennas on silicon substrate lenses at 620 GHz. The best double-sideband receiver noise temperature is less than 1300 K with a 3 dB bandwidth of ≈5 GHz. The gain bandwidth is 3.2 GHz. The mixer output noise dominated by thermal fluctuations is 50 K, and the intrinsic conversion gain is about −12 dB. Without mismatch losses and excluding the loss from the beamsplitter, we expect to achieve a receiver noise temperature of less than 700 K.
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Ekström H, Kollberg E, Yagoubov P, Gol'tsman G, Gershenzon E, Yngvesson S. Phonon cooled ultra thin NbN hot electron bolometer mixers at 620 GHz. In: Proc. 8th Int. Symp. Space Terahertz Technol.; 1997. p. 29–35.
Abstract: We have measured the noise performance and gain bandwidth of 35 A thin NbN hot-electron mixers integrated with spiral antennas on silicon substrate lenses at 620 GHz. A double-sideband receiver noise temperature less than 1300 K has been obtained with a 3 dB bandwidth of GHz. The gain bandwidth is 3.2 GHz. A lower noise temperature of 1100 K has been achieved with an improved set-up. The mixer output noise dominated by thermal fluctuations is about 50-60 K, and the SSB receiver and intrinsic conversion gain is about -18 and -12 dB, respectively. Without mismatch losses and excluding the loss from the beamsplitter, we expect to achieve a receiver noise temperature of less than 700 K.
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Ryabchun S, Tong C-YE, Blundell R, Kimberk R, Gol'tsman G. Study of the effect of microwave radiation on the operation of HEB mixers in the terahertz frequency range. IEEE Trans Appl Supercond. 2007;17(2):391–4.
Abstract: We have investigated the effect of injecting microwave radiation, with a frequency much lower than that corresponding to the energy gap of the superconductor, on the performance of the hot-electron bolometer mixer incorporated into a THz heterodyne receiver. More specifically, we show that exposing the mixer to microwave radiation does not cause a significant rise of the receiver noise temperature and fall of the mixer conversion gain so long as the microwave power is a small fraction of local oscillator power. The injection of a small, but controlled amount of microwave power therefore enables active compensation of local oscillator power and coupling fluctuations which can significantly degrade the gain stability of hot electron bolometer mixer receivers.
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Gol'tsman G, Kouminov P, Goghidze I, Gershenzon E. Nonequilibrium kinetic inductive response of YBCO thin films to low power laser pulses. IEEE Trans Appl Supercond. 1995;5(2):2591–4.
Abstract: We have discovered a transient nonequilibrium kinetic inductive voltage response of YBCO thin films to 20 ps pulses of YAG:Nd laser radiation with 0.63 /spl mu/m and 1.54 /spl mu/m wavelength. By increasing the sensitivity of the read-out system with 100 ps resolution time and diminishing the light intensity (fluence 0.1-2 /spl mu/J/cm/sup 2/) and transport current (density /spl les/10/sup 5/ A/cm/sup 2/) we were able to observe a peculiar bipolar signal form with nearly equal amplitudes for each sign. The integration of the kinetic inductive response over time gives the result which is qualitatively, of the same form as the response in the resistive and normal states: the nonequilibrium picosecond scale component is followed by the bolometric nanosecond component. The nonequilibrium response is interpreted as suppression of the order parameter by excess quasiparticles followed by a change both in resistance (for the resistive state) and in kinetic inductance (for the superconducting state).
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Meledin D, Tong CY-E, Blundell R, Kaurova N, Smirnov K, Voronov B, et al. The sensitivity and IF bandwidth of waveguide NbN hot electron bolometer mixers on MgO buffer layers over crystalline quartz. In: Harvard university, editor. Proc. 13th Int. Symp. Space Terahertz Technol. Cambridge, MA, USA; 2002. p. 65–72.
Abstract: We have developed and characterized waveguide phonon-cooled NbN Hot Electron Bolometer (FMB) mixers fabricated from a 3-4 nm thick NbN film deposited on a 200nm thick MgO buffer layer over crystalline quartz. Double side band receiver noise temperatures of 900-1050 K at 1.035 THz, and 1300-1400 K at 1.26 THz have been measured at an intermediate frequency of 1.5 GHz. The intermediate frequency bandwidth, measured at 0.8 THz LO frequency, is 3.2 GHz at the optimal bias point for low noise receiver operation.
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