We have observed the photon noise by measuring a response to the black body 350 GHz radiation and noise of the cold-electron bolometers (CEBs). The experimental results have been fit to the theoretical model of CEBs with two heat-balance equations. The measured noise has been decomposed into several terms with the help of theory. It is demonstrated that the photon noise exceeds any other noise components, which allows us to conclude that the bolometers measure the photon noise. Moreover, a peculiar shape of the noise dependence on the absorbed power originates completely from the photonic component according to the theory. In the additional experiment on heating of the cryostat plate together with the sample holder, we have observed the near independence of the noise on the electron temperature of the absorber, which has provided another proof of the presence of the photon noise in the first experiment. The least ratio between internal and photon noise equivalent powers, observed in our experiments, is 1.1 for the absorbed power of 1–2 pW.

We fabricated and experimentally studied a wideband metamaterial comprising a 2D array of annular antennas with Superconductor-Insulator-Normal metal-Insulator-Superconductor (SINIS) bolometers. The annular antenna array metamaterial was designed for a frequency range of 300–450 GHz and consists of periodically arranged electrically small rings, each containing two or four SINIS bolometers connected in series or parallel. These periodic structures with a unit cell size of about one-tenth of a wavelength act as a distributed absorber and receive two orthogonal polarizations. The unit’s small cell size provides a higher density of bolometers and therefore increases the bandwidth and the dynamic range of a single pixel. Theoretical estimates at a central frequency of 345 GHz yield absorption efficiencies of over 80% of the incident RF power within the 300–450 GHz frequency range. The average absorption by the metamaterial matrix in the given frequency band is at least twice as high in comparison to the half-wave circle matrix. We measured the optical response at sample temperatures as low as 100 mK using a quasi-optical setup that consisted of an immersion sapphire lens, bandpass mesh filters, and a variable temperature cryogenic blackbody radiation source. The measured series array voltage responsivity was 1.3 × 10⁹ V/W for radiation temperatures ranging from 2 K to 7.5 K. The current responsivity for the parallel array was 2.4 × 10⁴ A/W at a bath temperature of 100 mK. The spectral response was measured in a 240–370 GHz range with a Backward Wave Oscillator radiation source. The measured equivalent temperature sensitivity could be reduced to 100 μK/Hz^1/2 at a 2.7 K radiation temperature level, a value that is suitable for anisotropy measurements in cosmic microwave background radiation.

Current progress in the development of new subterahertz instruments discussed in this paper, including antennas, high-power gyrotrons, and low-noise receivers, provides a wide range of possible applications. Atmospheric absorption has now become a major limitation in the application of such high-performance subTHz systems, and the choice of the optimal location of antennas for astronomical, radar, and communication systems is important. The latest results of studying the microwave astroclimate in northern Eurasia are presented. Based on these studies, new perspectives and corrected plans for installing new antennas at the Suffa Plateau and in the Caucasus are formulated, and possible applications of new instruments such as radars for locating space debris and communication hubs for deep space communications, which are based on extremely-high-power gyrotrons and low-noise superconducting receivers, are discussed.

For improving the dynamic range and sensitivity at high power load we have integrated Superconductor-Insulator-Normal metal-Insulator-Superconductor (SINIS) bolometers with a Frequency Selective Surface (FSS) based distributed absorber formed by a series and parallel array consisting of 25 annular antenna elements, each containing two SINIS bolometers. By using a design with 50 bolometers we reduce incident power load on each bolometer, increase sensitivity and saturation power which is important for ground-based and balloon-borne telescopes with high background power loads. Our main detector pixel is optimized for a frequency band centered at 345 GHz. The detectors are matched to incoming telescope beam by a back-to-back horn with a back reflector. Such a configuration improves both the efficiency and the bandwidth of the receiver. Measured voltage responsivity approaches 2*109 V/W with an amplifier-limited voltage noise of 20 nV/Hz1/2, which corresponds to a NEP=10-17 W/Hz1/2. The linear voltage response for incoming power is observed for absorbed power of about 5 pW. The current responsivity for parallel array is 2*104 A/W and the shot noise limited intrinsic noise equivalent power is NEP=5*10-18 W/Hz1/2. The noise equivalent temperature difference is NETD=100 μK/Hz1/2 at 2.7 K background radiation temperature.

The article presents a brief review of cooling systems that ensure various temperature levels (from 0.1 K to 230 K) for radio astronomical receivers of photonic and electronic (or optical and radio) devices. The features of various cooling levels and the requirements for the design of the cooling systems are considered in detail, as well as the approaches to designing interfaces for cooled receivers: vacuum, cryogenic, electrical, mechanical, optical, and other interfaces required for effective operation. The presented approaches to design are illustrated by a series of joint developments of the authors carried out over the past 45 years, including those produced over the past year.

This review presents the main characteristics and mechanisms of operation of superconductor–insulator–normal metal–insulator–superconductor (SINIS) microwave detectors. An analysis of the detectors’ performance against a quantum detector and a photon counter is given. Methods for cooling a superconductor using normal metal traps and the role of electron cooling in optimizing the current response to terahertz radiation are discussed. Fabrication methods using shadow evaporation as well as magnetron sputtering are described.