Nebosis, R. S., Heusinger, M. A., Schatz, W., Renk, K. F., Gol’tsman, G. N., Karasik, B. S., et al. (1993). Ultrafast photoresponse of a structured YBa2Cu3O7-δ thin film to ultrashort FIR laser pulses. IEEE Trans. Appl. Supercond., 3(1), 2160–2162.
Abstract: The authors have investigated the photoinduced voltage response of a current-carrying structured YBa2Cu3O7-δ thin film to ultrashort far-infrared (FIR) laser pulses in the frequency range from 0.7 THz to 7 THz. The detector has shown an almost constant sensitivity of 1 mV/W and a noise equivalent power of less than 5*10/sup -7/ W/ square root Hz. The temperature dependence of the decay time of the detector signal was studied for temperatures around the transition temperature of the film ( approximately 80 K). For a detector temperature where dR/dT had its maximum, the authors observed bolometric signals with decay times of about 2 ns, and for lower temperatures they observed nonbolometric signals with decay times of approximately 120 ps; the duration of the nonbolometric signals was limited by the time resolution of the electronic registration equipment.
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Semenov, A. D., Goghidze, I. G., Gol’tsman, G. N., Sergeev, A. V., Aksaev, E. E., & Gershenzon, E. M. (1993). Non-equilibrium quasiparticle response to radiation and bolometric effect in YBaCuO films. IEEE Trans. Appl. Supercond., 3(1), 2132–2135.
Abstract: The voltage photoresponse of structured current biased YBCO films on different substrates to 20-ps laser pulses of 0.63- mu m and 1.54- mu m wavelengths and to continuously modulated radiation of 2-mm wavelength is measured to temperatures around Tc. Fast picosecond decay of the response to pulsed radiation is followed by slow exponential relaxation with a nanosecond characteristic time depending on the substrate material and film dimensions. The slow component does not depend on wavelength and is attributed to the bolometric effect, while the magnitude of the fast component associated with nonequilibrium response rises with wavelength. More than an order-of-magnitude increase of the nonequilibrium response is seen from near-infrared to millimeter-wave range. This dependence plausibly reflects the low efficiency of multiplication of photoexcited electrons in YBaCuO compared to conventional superconductors.
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Gershenzon, E. M., Gershenzon, M. E., Goltsman, G. N., Semenov, A. D., & Sergeev, A. V. (1991). Wide-band highspeed Nb and YBaCuO detectors. IEEE Trans. Magn., 27(2), 2836–2839.
Abstract: The physical limitations on the response time and the nature of nonequilibrium detection of radiation were investigated for Nb and YBCO film in a wide spectral range from millimeter to near-infrared wavelengths. In the case of ideal heat removal from the film, the detection mechanism is connected with an electron heating effect which is not selective over a wide spectral interval. For Nb, the dependence of the response time on the electron mean free path l and temperature T is tau varies as T/sup -2/l/sup -1/. The values of detectivity D* and tau are 3*10/sup 11/ W/sup -1/ Hz/sup 1/2/ cm and 5*10/sup -9/ s at T=1.6 K, respectively. For YBCO film the tau value of 1-2 ps at T=77 K was obtained; the NEP value of 3*10/sup -11/ W-Hz/sup -1/2/ can be obtained at T=77 K in the case of the optimal film matching to the radiation.
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Gershenzon, E. M., Gol’tsman, G. N., Gousev, Y. P., Elant’ev, A. I., & Semenov, A. D. (1991). Electromagnetic radiation mixer based on electron heating in resistive state of superconductive Nb and YBaCuO films. IEEE Trans. Magn., 27(2), 1317–1320.
Abstract: A theory of an electron-heating mixer which makes it possible to calculate all the characteristics of the device is developed. It is shown that positive conversion gain is possible for such a mixer in the millimeter to near-infrared wavelength range. The dynamic range and the optimum heterodyne power can be selected from a very wide interval by varying the mixing element volume. Measurements made for Nb within the frequency range of 120-750 GHz confirm the theory. The conversion loss obtained at T=1.6 K and normalized to the element reaches 0.3 dB in the intermediate frequency band of 40 MHz; the possible noise temperature is 50 K. The estimation of noise temperature and output band for YBaCuO at T=77 yields 200 K and more than 10 GHz, respectively.
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Gershenzon, E. M., Gol’tsman, G. N., Semenov, A. D., & Sergeev, A. V. (1991). Mechanism of picosecond response of granular YBaCuO films to electromagnetic radiation. IEEE Trans. Magn., 27(2), 1321–1324.
Abstract: Ultrafast mechanisms of radiation detection in granular YBaCuO films are studied in the wide wavelength range from millimeter waves to near infrared. With an increase in radiation frequency, the Josephson detection at the grain-boundary weak links is replaced by electron heating into the grains. This change occurs in the submillimeter wavelength range. The electron-phonon relaxation time tau /sub eph/ is determined from direct measurements, quasi-stationary electron heating measurements, and the frequency dependence of the current at which maximum voltage shift is observed. The temperature dependence of tau /sub eph/ at T<or=40 K was found to be tau /sub eph/ approximately T/sup -1/. The results show that detectors with a response time of a few picoseconds at nitrogen temperature are attainable.
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