Флуктуационная чувствительность сверхпроводящего болометрического смесителя на эффекте разогрева электронного газа
Interest in research in the terahertz range is driven by a great number of various applications, where terahertz instruments may play a leading role. To name just a few, such applications include study of the cosmic microwave background radiation and the distribution of the dark matter, medicine, navigation, fire alarm, security systems and environmental monitoring. The paper discusses the possibility of using a receiver based on the hot-electron effect in superconducting films as an imaging system. We present the results of the noise equivalent temperature difference (NETD) measurements performed with a hot-electron bolometer mixer made from a thin superconducting film. The receiver with a noise temperature of ~ 3800 K at a local oscillator frequency of 300 GHz a bandwidth of 500 MHz and an integration time of 1 s has offered an NETD of 0.5 K. We have also developed a technique that enabled us to reduce the contribution of the mixer gain fluctuations to the overall system instability. As of this writing, the above value of the NETD is the lowest value offered for this type of receiver, which indicates the possibility to use such receivers in real-time imaging systems. The technique offered in the paper for achieving the limiting value of the NETD offers an alternative to the phase-locking scheme.
In this paper, the dispersion characteristics of slow-wave structures suitable for use in devices in the terahertz range are calculated. Slow-wave structures of “winding waveguide” and “counter pins” types can be considered as suitable systems. Analysis of dispersion characteristics of slow-wave structure was carried out by a waveguide-resonator model, which is built for the slow-wave structure of “winding waveguide”-type taking into account a channel for the electron beam. Waveguide-resonator model is consisted of quadripoles which describe the waveguide segments. This model is most accurately reflects the structure of the field in the winding waveguide. Dispersion characteristics were calculated according to the program stated in this paper. These characteristics are used to construct model of millimeter traveling-wave tube, which is in this case the chain of quadripoles. The most common in the solution of these problems is the discrete approach . The difference form of electrodynamic theory of excitation is used to justify the use of a mathematical model of the discrete interaction description .
We characterize superconducting antenna-coupled NbN hot-electron bolometer (HEB) for direct detection of THz radiation operating at a temperature of 9.0 K. At signal frequency of 2.5 THz, the measured value of the optical noise equivalent power is 2.0×10-13 W-Hz-0.5. The estimated value of the energy resolution is about 1.5 aJ. This value was confirmed in the experiment with pulsed 1.55-μm laser employed as a radiation source. The directly measured detector energy resolution is 2 aJ. The obtained risetime of pulses from the detector is 130 ps. This value was determined by the properties of the RF line. These characteristics make our detector a device-of-choice for a number of practical applications associated with detection of short THz pulses.
We report on the development of a highly sensitive optical receiver for heterodyne IR spectroscopy at the communication wavelength of 1.5 μm (200 THz) by use of a superconducting hot-electron bolometer. The results are important for the resolution of narrow spectral molecular lines in the near-IR range for the study of astronomical objects, as well as for quantum optical tomography and fiber-optic sensing. Receiver configuration as well as fiber-to-detector light coupling designs are discussed. Light absorption of the superconducting detectors was enhanced by nano-optical antennas, which were coupled to optical fibers. An intermediate frequency (IF) bandwidth of about 3 GHz was found in agreement with measurements at 300 GHz, and a noise figure of about 25 dB was obtained that was only 10 dB above the quantum limit.
In this paper, dispersion characteristics of "serpentine”-type slow-wave structures, which are promising for the terahertz range use, are calculated. For 3D-modeling, HFSS was used. Program described in work was used in the calculation. Using the obtained characteristics, octopole chain model of the slow-wave structure is constructed. Discrete approach is advisable in solving these problems. Justification of the applied mathematical model for the discrete interaction follows from the difference form of electrodynamic theory of excitation . Requirements to coefficients of the resulting finite-difference equation are high, because their accuracy determines how close the mathematical model of the discrete interaction to the physical laws is. These coefficients have a certain electrodynamic sense and are obtained through the octopole transmission matrix coefficients. In turn, this octopole is a mathematical model of the resonator slow-wave structure cell.
The problem of designing stabilizing resonator (SR) for a 4-mm wavelengths range coaxial magnetron with low level of output power has been considered. The recommendations for choosen the coaxial resonator external to internal diameter relations depending on technical project requirements are developed.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.