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Baselmans, J., Kooi, J., Baryshev, A., Yang, Z. Q., Hajenius, M., Gao, J. R., et al. (2005). Full characterization of small volume NbN HEB mixers for space applications. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 457–462). Göteborg, Sweden.
Abstract: NbN phonon cooled HEB’s are one of the most promising bolometer mixer technologies for (near) future (space) applications. Their performance is usually quantified by mea- suring the receiver noise temperature at a given IF frequency, usually around 1 – 2 GHz. However, for any real applications it is vital that one fully knows all the relevant properties of the mixer, including LO power, stability, direct detection, gain bandwidth and noise bandwidth, not only the noise temperature at low IF frequencies. To this aim we have measured all these parameters at the optimal operating point of one single, small volume quasioptical NbN HEB mixer. We find a minimum noise temperature of 900 K at 1.46 THz. We observe a direct detection effect indicated by a change in bias current when changing from a 300 K hot load to a 77 K cold load. Due to this effect we overestimate the noise temperature by about 22% using a 300 K hot load and a 77 K cold load. The LO power needed to reach the optimal operating point is 80 nW at the receiver lens front, 59 nW inside the NbN bridge. However, using the isothermal technique we find a power absorbed in the NbN bridge of 25 nW, a difference of about a factor 2. We obtain a gain bandwidth of 2.3 GHz and a noise bandwidth of 4 GHz. The system Allan time is about 1 sec. in a 50 MHz spectral bandwidth and a deviation from white noise integration (governed by the radiometer equation) occurs at 0.2 sec., which implies a maximum integration time of a few seconds in a 1 MHz bandwidth spectrometer.
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Bueno, J., Coumou, P. C. J. J., Zheng, G., de Visser, P. J., Klapwijk, T. M., Driessen, E. F. C., et al. (2014). Anomalous response of superconducting titanium nitride resonators to terahertz radiation. Appl. Phys. Lett., 105, 192601 (1 to 5).
Abstract: We present an experimental study of kinetic inductance detectors (KIDs) fabricated of atomic layer deposited TiN films and characterized at radiation frequencies of 350 GHz. The responsivity to radiation is measured and found to increase with the increase in radiation powers, opposite to what is expected from theory and observed for hybrid niobium titanium nitride/aluminium (NbTiN/Al) and all-aluminium (all-Al) KIDs. The noise is found to be independent of the level of the radiation power. The noise equivalent power improves with higher radiation powers, also opposite to what is observed and well understood for hybrid NbTiN/Al and all-Al KIDs. We suggest that an inhomogeneous state of these disordered superconductors should be used to explain these observations.
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Floet, D. W., Baselmans, J. J. A., Klapwijk, T. M., & Gao, J. R. (1998). Resistive transition of niobium superconducting hot-electron bolometer mixers. Appl. Phys. Lett., 73(19), 2826.
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Gao, G. R., Hovenier, J. N., Yang, Z. Q., Baselmans, J. J. A., Baryshev, A., Hajenius, M., et al. (2005). A novel terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 19–23). Göteborg, Sweden.
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Gao, J. R., Hovenier, J. N., Yang, Z. Q., Baselmans, J. J. A., Baryshev, A., Hajenius, M., et al. (2005). Terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer. Appl. Phys. Lett., (86).
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