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Baselmans JJA, Baryshev A, Reker SF, Hajenius M, Gao JR, Klapwijk TM, et al. Influence of the direct response on the heterodyne sensitivity of hot electron bolometer mixers. J Appl Phys. 2006;100(8):084510 (1 to 7).
Abstract: We present a detailed experimental study of the direct detection effect in a small volume (0.15μm×1μm×3.5nm) quasioptical NbN phonon cooled hot electron bolometer mixer at 673GHz. We find that the small signal noise temperature, relevant for an astronomical observation, is 20% lower than the noise temperature obtained using 300 and 77K calibration loads. In a separate set of experiments we show that the direct detection effect is caused by a combination of bias current reduction when switching from the 77 to the 300K
load in combination with the bias current dependence of the receiver gain. The bias current dependence of the receiver gain is shown to be mainly caused by the current dependence of the mixer gain.
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Hajenius M, Barends R, Gao JR, Klapwijk TM, Baselmans JJA, Baryshev A, et al. Local resistivity and the current-voltage characteristics of hot electron bolometer mixers. IEEE Trans Appl Supercond. 2005;15(2):495–8.
Abstract: Hot-electron bolometer devices, used successfully in low noise heterodyne mixing at frequencies up to 2.5 THz, have been analyzed. A distributed temperature numerical model of the NbN bridge, based on a local electron and a phonon temperature, is used to model pumped IV curves and understand the physical conditions during the mixing process. We argue that the mixing is predominantly due to the strongly temperature dependent local resistivity of the NbN. Experimentally we identify the origins of different transition temperatures in a real HEB device, suggesting the importance of the intrinsic resistive transition of the superconducting bridge in the modeling.
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Baselmans JJA, Baryshev A, Reker SF, Hajenius M, Gao JR, Klapwijk TM, et al. Direct detection effect in small volume hot electron bolometer mixers. Appl Phys Lett. 2005;86(16):163503 (1 to 3).
Abstract: We measure the direct detection effect in a small volume (0.15μm×1μm×3.5nm)(0.15μm×1μm×3.5nm) quasioptical NbN phonon cooled hot electronbolometermixer at 1.6THz1.6THz. We find that the small signal sensitivity of the receiver is underestimated by 35% due to the direct detection effect and that the optimal operating point is shifted to higher bias voltages when using calibration loads of 300K300K and 77K77K. Using a 200GHz200GHzbandpass filter at 4.2K4.2K the direct detection effect virtually disappears. This has important implications for the calibration procedure of these receivers in real telescope systems.
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Baselmans JJA, Hajenius M, Gao JR, Klapwijk TM, de Korte PAJ, Voronov B, et al. Doubling of sensitivity and bandwidth in phonon cooled hot electron bolometer mixers. Appl Phys Lett. 2004;84(11):1958–60.
Abstract: We demonstrate that the performance of NbN lattice cooled hot electron bolometer mixers depends strongly on the interface quality between the bolometer and the contact structure. We show experimentally that both the receiver noise temperature and the gain bandwidth can be improved by more than a factor of 2 by cleaning the interface and adding an additional superconducting interlayer to the contact pad. Using this we obtain a double sideband receiver noise temperature TN,DSB=950 K
at 2.5 THz and 4.3 K, uncorrected for losses in the optics. At the same bias point, we obtain an IF gain bandwidth of 6 GHz.
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Gao GR, Hovenier JN, Yang ZQ, Baselmans JJA, Baryshev A, Hajenius M, et al. A novel terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer. In: Proc. 16th Int. Symp. Space Terahertz Technol. Göteborg, Sweden; 2005. p. 19–23.
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Yates SJC, Baryshev AM, Baselmans JJA, Klein B, Güsten R. Fast Fourier transform spectrometer readout for large arrays of microwave kinetic inductance detectors. Appl Phys Lett. 2009;95(4):3.
Abstract: Microwave kinetic inductance detectors have great potential for large, very sensitive detector arrays for use in, for example, submillimeter imaging. Being intrinsically readout in the frequency domain, they are particularly suited for frequency domain multiplexing allowing ~1000 s of devices to be readout with one pair of coaxial cables. However, this moves the complexity of the detector from the cryogenics to the warm electronics. We present here the concept and experimental demonstration of the use of fast Fourier transform spectrometer readout, showing no deterioration of the noise performance compared to the low noise analog mixing while allowing high multiplexing ratios.
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Gao JR, Hovenier JN, Yang ZQ, Baselmans JJA, Baryshev A, Hajenius M, et al. Terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer. Appl Phys Lett. 2005;86:244104 (1 to 3).
Abstract: We report the first demonstration of an all solid-stateheterodyne receiver that can be used for high-resolution spectroscopy above 2THz suitable for space-based observatories. The receiver uses a NbN superconducting hot-electron bolometer as mixer and a quantum cascade laser operating at 2.8THz as local oscillator. We measure a double sideband receiver noise temperature of 1400K at 2.8THz and 4.2K, and find that the free-running QCL has sufficient power stability for a practical receiver, demonstrating an unprecedented combination of sensitivity and stability.
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Klapwijk TM, Barends R, Gao JR, Hajenius M, Baselmans JJA. Improved superconducting hot-electron bolometer devices for the THz range. In: Proc. SPIE. Vol 5498.; 2004. p. 129–39.
Abstract: Improved and reproducible heterodyne mixing (noise temperatures of 950 K at 2.5 THz) has been realized with NbN based hot-electron superconducting devices with low contact resistances. A distributed temperature numerical model of the NbN bridge, based on a local electron and a phonon temperature, has been used to understand the physical conditions during the mixing process. We find that the mixing is predominantly due to the exponential rise of the local resistivity as a function of electron temperature.
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