Baubert, J., Salez, M., Delorme, Y., Pons, P., Goltsman, G., Merkel, H., et al. (2003). Membrane-based HEB mixer for THz applications. In J. - C. Chiao, V. K. Varadan, & C. Cané (Eds.), Proc. SPIE (Vol. 5116, pp. 551–562). SPIE.
Abstract: We report in this paper a new concept for 2.7 THz superconducting Niobium nitride (NbN) Hot-Electron Bolometer mixer (HEB). The membrane process was developped for space telecommnunication applications a few years ago and the HEB mixer concept is now considered as the best choice for low-noise submillimeter-wave frequency heterodyne receivers. The idea is then to join these two technologies. The novel fabrication scheme is to fabricate a NbN HEB mixer on a 1 μm thick stress-less Si3N4/SiO2 membrane. This seems to present numerous improvements concerning : use at higher RF frequencies, power coupling efficiency, HEB mixer sensitivity, noise temperature, and space applications. This work is to be continued within the framework of an ESA TRP project, a 2.7 THz heterodyne camera with numerous applications including a SOFIA airborne receiver. This paper presents the whole fabrication process, the validation tests and preliminary results. Membrane-based HEB mixer theory is currently being investigated and further tests such as heterodyne and Fourier transform spectrometry measurement are planed shortly.
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Baeva, E. M., Titova, N. A., Veyrat, L., Sacépé, B., Semenov, A. V., Goltsman, G. N., et al. (2021). Thermal relaxation in metal films bottlenecked by diffuson lattice excitations of amorphous substrates. arXiv:2101.07071v1 [cond-mat.mtrl-sci].
Abstract: Here we examine the role of the amorphous insulating substrate in the thermal relaxation in thin NbN, InOx, and Au/Ni films at temperatures above 5 K. The studied samples are made up of metal bridges on an amorphous insulating layer lying on or suspended above a crystalline substrate. Noise thermometry was used to measure the electron temperature Te of the films as a function of Joule power per unit of area P2D. In all samples, we observe the dependence P2D∝Tne with the exponent n≃2, which is inconsistent with both electron-phonon coupling and Kapitza thermal resistance. In suspended samples, the functional dependence of P2D(Te) on the length of the amorphous insulating layer is consistent with the linear T-dependence of the thermal conductivity, which is related to lattice excitations (diffusons) for the phonon mean free path smaller than the dominant phonon wavelength. Our findings are important for understanding the operation of devices embedded in amorphous dielectrics.
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Varyukhin, S. V., Zakharov, A. A., Gershenzon, E. M., Gol'tsman, G. N., Ptitsyna, N. G., & Chulkova, G. M. (1990). AC losses and submillimeter absorption in single crystals La2CuO4. Phys. B Condens. Mat., 165-166, 1269–1270.
Abstract: The La2CuO4 single crystals were used to carry out the measurements of transmission spectra within the submillimeter range of wavelengths, as well as the capacitance C and conductivity G in the region of acoustic frequencies of the metal-dielectric-La2Cu04 system at low temperatures. The optical spectra display a threshold character. There takes place a sharp decreasing of transmission signal in the energy range of hυ>1.5meV. The C(ω,T) and G(ω,T) dependences have a universal form characteristic of relaxation processes of the Debye type. The relaxation time dependence displays a thermoactivation character τ(T)-exp(ξ/T) with a gap value of ξ≃2meV,coinciding with the optical one. It is assumed that there exist excitations with a characteristic energy ~ 2meV in La2Cu04.A possible nature of the revealed low-energy excitations is discussed.
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Varyukhin, S. V., Zakharov, A. A., Gershenzon, E. M., Gol'tsman, G. N., Ptitsina, N. G., & Chulkova, G. M. (1990). Low energy excitation in La2CuO4. Sverkhprovodimost': Fizika, Khimiya, Tekhnika, 3(5), 832–837.
Abstract: Measurements of transmission and photoconductivity spectra in submillimeter wave length range as well as of capacity C and conductivity G in the region of acoustic frequencies of metal-dielectric-La2CuO4 system at low temperatures are performed using La2CuO4 monocrystals. Optical spectra posses a threshold character, a sharp decrease of transmission and photocoductivity signal occurs in the energy region hν>1.5 MeV. C(ω,T) and G(ω, T) dependences have a universal form typical of Debye type relaxation processes. Relaxation time dependence is of thermoactivated character τ(T)∼exp(ξ/T) with the gap value ξ≅2 meV. It is assumed that excitations with characteristic energy of ∼2 meV exist in La2CuO4. A possible nature of the detected low-energy excitations is discussed.
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Elezov, M. S., Scherbatenko, M. L., Sych, D. V., & Goltsman, G. N. (2018). Active and passive phase stabilization for the all-fiber Michelson interferometer. In J. Phys.: Conf. Ser. (Vol. 1124, 051014 (1 to 5)).
Abstract: We put forward two methods for phase stabilization in the all-fiber Michelson interferometer. To perform passive phase stabilization, we use a heat bath for all fibers and electro-optical components, and put the interferometer in a hermetic case. To perform active phase stabilization, we monitor output power of the interferometer and develop an electronic feedback control. The phase stabilization methods enable stable interference pattern for several minutes, and can be helpful for the development of the optimal quantum receiver for coherent signals.
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