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Semenov, A. D., Gousev, Y. P., Nebosis, R. S., Renk, K. F., Yagoubov, P., Voronov, B. M., et al. (1996). Heterodyne detection of THz radiation with a superconducting hot‐electron bolometer mixer. Appl. Phys. Lett., 69(2), 260–262.
Abstract: We report on the use of a superconducting hot‐electron bolometer mixer for heterodyne detection of terahertz radiation. Radiation with a wavelength of 119 μm was coupled to the mixer, a NbN microbridge, by a hybrid quasioptical antenna consisting of an extended hyperhemispherical lens and a planar logarithmic spiral antenna. We found, at an intermediate frequency of 1.5 GHz, a system double side band noise temperature of ≊40 000 K and conversion losses of 25 dB. We also discuss the possibilities of further improvement of the mixer performance.
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Trifonov, V. A., Karasik, B. S., Zorin, M. A., Gol’tsman, G. N., Gershenzon, E. M., Lindgren, M., et al. (1996). 9.6 μm wavelength mixing in a patterned YBa2Cu3O7‐δ thin film. Appl. Phys. Lett., 68(10), 1418–1420.
Abstract: Hot‐electron bolometric (HEB) mixing of 9.6 μm infrared radiation from two lasers in high‐quality YBa2Cu3O7−δ (YBCO) patterned thin film has been demonstrated. A heterodyne measurement showed an intermediate frequency (IF) bandwidth of 18 GHz, limited by our measurement system. An intrinsic limit of 100 GHz is predicted. Between 0.1 and 1 GHz intermediate frequency, temperature fluctuations with an equivalent output noise temperature Tfl up to ∼150 K, contributed to the mixer noise while Johnson noise dominated above 1 GHz. The overall conversion loss at 77 K at low intermediate frequencies was measured to be ∼25 dB, of which 13 dB was due to the coupling loss. The HEB mixer is very promising for use in heterodyne receivers within the whole infrared range.
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Lindgren, M., Trifonov, V., Zorin, M., Danerud, M., Winkler, D., Karasik, B. S., et al. (1994). Transient resistive photoresponse of YBa2Cu3O7−δ films using low power 0.8 and 10.6 μm laser radiation. Appl. Phys. Lett., 64(22), 3036–3038.
Abstract: Thin YBa2Cu3O7−δ laser deposited films were patterned into devices consisting of ten parallel 1 μm wide strips. Nonequilibrium picosecond and bolometric photoresponses were studied by the use of 17 ps full width at half‐maximum laser pulses and amplitude modulated radiation from an AlGaAs laser up to 10 GHz and from a CO2 laser up to 1 GHz. The time and frequency domain measurements were in agreement. The fast response can be explained by electron heating. The use of low optical power and a sensitive measurement system excluded any nonlinear transient processes and kinetic inductance changes in the superconducting state. At 1 GHz modulation frequency, the responsivity was ∼1.2 V/W both for 0.8 and 10.6 μm wavelengths. The sensitivity of a fast and spectrally broadband infrared detector is discussed.
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Semenov, A. D., Goghidze, I. G., Gol’tsman, G. N., Sergeev, A. V., & Gershenzon, E. M. (1993). Evidence for the spectral dependence of nonequilibrium picosecond photoresponse of YBaCuO thin films. Appl. Phys. Lett., 63(5), 681–683.
Abstract: The transient voltage photoresponse of current biased YBaCuO thin films to 20 ps laser pulses of 0.63 and 1.54 μm wavelengths is measured for temperatures around the superconducting transition region. The fast picosecond decay of the response is followed by a slow nanosecond relaxation which is associated with the bolometric effect. The magnitude of the fast component of the response varies in proportion to the square root of wavelength that plausibly reflects multiplication processes of photoexcited electrons via electron–electron scattering and interaction with high energy phonons.
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Semenov, A. D., Gol’tsman, G. N., Gogidze, I. G., Sergeev, A. V., Gershenzon, E. M., Lang, P. T., et al. (1992). Subnanosecond photoresponse of a YBaCuO thin film to infrared and visible radiation by quasiparticle induced suppression of superconductivity. Appl. Phys. Lett., 60(7), 903–905.
Abstract: We observed subnanosecond photoresponse of a structured superconducting YBa2Cu3O7−δ thin film to infrared and visible radiation. We measured the voltage response of a current biased film (thickness 700 Å) in a resistive state to radiation pulses. From our results we conclude a response time of about 90 ps and a responsivity of about 4×1010 Ω/J. We attribute the response to Cooper pair breaking and suppression of the superconducting energy gap induced by nonequilibrium quasiparticles.
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