Microwave Receiving System Based on Cryogenic Sensors for the Optical Big Telescope Alt-Azimuth.

This article presents the results of evaluating the possibility of conducting radio astronomy studies in the windows of atmospheric transparency ~100, ~230, and ~350 GHz using the optical Big Telescope Alt-Azimuthal (BTA) of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). A list of some promising astronomical tasks is proposed. The astroclimat conditions at the BTA site and possible optical, cryogenic, and mechanical interfaces for mounting a superconducting radio receiver at the focus of the optical telescope are considered. As a receiving system, arrays of detectors cooled to ~0.3 K based on the superconductor-insulator-normal metal-insulator-superconductor (SINIS) structure are proposed. The implementation of the project will make it possible to use the BTA site of the SAO RAS not only to solve some astronomical problems (it is possible to consider the implementation of a single observatory, the VLBI (very-long-baseline interferometry) mode in the Suffa, EHT (Event Horizon Telescope), and Millimetron projects), but it will also be used to test various cryogenic detectors in a real observatory.

High-resolution astronomical spectrograph design method with a single echelle grating.

The paper presents a method for calculation of the main paraxial and energy parameters of a high-resolution astronomical spectrograph with a single echelle grating in a wide spectral range, without cross-dispersion elements. We consider two variants of the system design, namely, with a fixed grating (spectrograph) and with a movable grating (monochromator). Based on the analysis of the spectral resolution dependence on the echelle grating characteristics and the collimated beam diameter, the limits of the achievable maximum spectral resolution of the system are determined. The results obtained in this work can simplify the choice of the starting point for spectrograph designing. As an example of the presented method application design of the spectrograph for the Large Solar Telescope-coronagraph LST-3, operating in the spectral range of 390-900 nm, with spectral resolving power of R=200,000 and minimum diffraction efficiency of the echelle grating I g>0.68, is considered.

Advanced modeling of a moderate-resolution holographic spectrograph.

In the present article we consider an accurate modeling of a spectrograph with a cascade of volume-phase holographic gratings. The proposed optical scheme allows us to detect spectra in an extended wavelength range without gaps, providing relatively high spectral resolution and high throughput. However, modeling and minimization of possible cross-talk between gratings and stray light in such a scheme represents a separate task. We use analytical equations of the coupled-wave theory together with rigorous coupled-wave analysis to optimize the gratings parameters and further apply the latter together with a non-sequential ray-tracing algorithm to model propagation of beams through the spectrograph. The results show relatively high throughput up to 53% and the absence of any significant cross-talk or ghost images, even for ordinary holograms recorded on dichromated gelatin.