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The origin and nature of ultra-high-energy cosmic rays (UHECRs) remain an open question in astroparticle physics. Motivated by the need for an unprecedented aperture for further advancements, the Fluorescence detector Array of Single-pixel Telescopes (FAST) is a prospective next-generation, ground-based UHECR observatory that aims to cover a huge area by deploying a large array of low-cost fluorescence detectors. The full-scale FAST prototype consists of four 20 cm photomultiplier tubes at the focus of a segmented mirror 1.6 m in diameter. Over the last five years, three prototypes have been installed at the Telescope Array Experiment in Utah, USA, and one prototype at the Pierre Auger Observatory in Mendoza, Argentina, commencing remote observation of UHECRs in both hemispheres. We report on the latest results of these FAST prototypes, including telescope calibrations, atmospheric monitoring, ongoing electronics upgrades, development of sophisticated reconstruction methods, and UHECR detections., Comment: 8 pages, 6 figures, Proceedings of the 37th International Cosmic Ray Conference (ICRC 2021)

Nowadays, the need for extended uniform light sources increases in many different areas of optics. Integrating spheres show one of the best properties among them. The paper is focused on verification of the practical use of so-called general purpose integrating spheres for the purpose of the calibration of highly sensitive detectors in the near-UV spectrum. To achieve this, the summarization of the theory of the integrating spheres is given, the methodology of the measurement is described and a universal experimental setup is designed. The setup is able to measure the real spatial and angular radiance uniformity of the exit port of selected representative of integrating spheres. The results of radiance uniformity measurements are graphically presented and discussed.

The origin and nature of ultra-high energy cosmic rays (UHECRs) are hot topics in the astroparticle physics community. The Fluorescence detector Array of Single-pixel Telescopes (FAST) is a design for a next-generation ground-based UHECR observatory, addressing the requirements for a large-area, low-cost detector suitable for measuring the properties of the highest energy cosmic rays with an unprecedented aperture. We have developed a full-scale prototype consisting of four 200 mm photomultiplier tubes at the focus of a segmented mirror of 1.6 m in diameter. Over the last three years, we have installed three prototypes at the Telescope Array Experiment in Utah, USA. These telescopes have been steadily taking data since installation. We report on preliminary results of the full-scale FAST prototypes, including measurements of UHECRs, and distant ultraviolet lasers used to study the atmospheric transparency. Furthermore, we discuss the installation of an additional identical FAST prototype at the Pierre Auger Observatory in Argentina. Possible benefits to the Telescope Array Experiment and the Pierre Auger Observatory include a comparison of the transparency of the atmosphere above both experiments, a study of the systematic uncertainty associated with their existing fluorescence detectors, and a cross-calibration of their energy and Xmax scales.

The Fluorescence detector Array of Single-pixel Telescopes (FAST) is a proposed large-area, next-generation experiment for the detection of ultra-high energy cosmic rays via the atmospheric fluorescence technique. The telescope’s large field-of-view (30 ×30) is imaged by four 200 mm photomultiplier-tubes at the focal plane of a segmented spherical mirror of 1.6 m diameter. Two prototypes are installed and taking data at the Black Rock Mesa site of the Telescope Array experiment in central Utah, USA. We present the process used for optimization of the optical performance of this compact and low-cost telescope, which is based on a simulation of the telescope’s optical point spread function.

We present the opto-mechanical design of a new generation fluorescence telescope for the de- tection of ultrahigh-energy cosmic rays (UHECRs). The Fluorescence detector Array of Single- pixel Telescopes (FAST) is a proposed low-cost, large-area, next-generation experiment for the detection of UHECRs via the atmospheric fluorescence technique. The telescope is of a simpli- fied Schmidt design, suitable for a camera consisting of only a few large pixels. The telescope has a 1 m2 entrance aperture, and a field-of-view of 30◦ × 30◦ . We present the optical design of the prototype telescope as well as the mirror alignment and pointing calibration procedures. The prototype of the FAST telescope is installed at the Black Rock Mesa site of the Telescope Array Experiment.

We present a concept for large-area, low-cost detection of ultrahigh-energy cosmic rays (UHECRs) with a Fluorescence detector Array of Single-pixel Telescopes (FAST), addressing the requirements for the next generation of UHECR experiments. In the FAST design, a large field of view is covered by a few pixels at the focal plane of a mirror or Fresnel lens. We report on the first results of a FAST prototype installed at the Telescope Array (TA) site, consisting of a single 200 mm photomultiplier tube (PMT) at the focal plane of a 1 m2 Fresnel lens system taken from the prototype of the JEM-EUSO experiment. We also report on the status of the full-scale FAST prototype soon to be installed at the TA site, comprising a segmented spherical mirror of 1.6 m diameter and a 2 × 2 PMT camera.

Two measuring techniques are presented in this paper. These techniques are able to measure and process the shape of the reflecting surfaces. In the first part of the paper the theory and modifications of the optical, mechanical and software design for the Hartmann wavefront analyzer are described. This new method is applied to the non-contact measurement of concave-mirrors shape and objectively defines the shape and specifies the difference of the segment shape from an ideal surface with micrometer accuracy. This difference determines essentially the mirrors image quality. In the second part of the paper attention is concentrated on the other main factor that affects image quality— surface roughness. Thereinafter, physical background and usage of the measuring system and results are presented.

This paper refers to the construction and utilization of the chamber that has been used for measurement of fluorescence yield within the frame of the project AIRFLY. The chamber was designed to simulate some physical conditions in high levels of the atmosphere, particularly pressure, temperature and humidity. The aim of the AIRFLY (AIR FLuorescence Yield) project is to simulate and to measure the process of the fluorescence and Cherenkov emission produced by impact of high-energy cosmic rays (UHECR) on molecules of nitrogen in high levels of the atmosphere. This is required for calibration of fluorescence detectors (FDs) dedicated for monitoring particles of these energies by means of fluorescence measurements.

The Fluorescence detector Array of Single-pixel Telescopes is a proposed low-cost, large-area, next-generation experiment for the detection of ultrahigh-energy cosmic rays via the atmospheric fluorescence technique. The proposed design involves the deployment of several hundred large field-of-view fluorescence telescopes on a regular grid of several thousand square kilometers in ground area. This paper describes the optical design of the prototype telescope, as well as its mechanical support structure.

The goal of the ELI (Extreme Light Infrastructure) project is to build a laser centre with the worlds highest power output pulsed laser in the locality of Dolni Břežany near Prague. Presented paper offers first glance to the insight into continuous and pulsed beam interaction with various optical systems which causes beam's spatial and temporal transformation. Complexity of this problem is illustrated in need of geometrical and physical optics knowledge, numerical simulations, material engineering and many others. This paper is focused on the field trace simulations in various software environments for both simple and more complex optical systems.

Water Cherenkov detectors are used for studying of high energy cosmic rays. The photomultiplier tubes observe the Cherenkov light generated by fast extensive air shower of charged particles in water. Material trade-named Tyvek is frequently used as the inner lining material of these Cherenkov detectors because a high diffuse reflectivity is required in order to improve light collection uniformity. The results of Tyvek surface microstructure measurement using optical (confocal microscopy) and mechanical (profilometry) methods are presented in this paper. Tyvek surface light scattering anisotropy is commented.

The Geant4 toolkit is important and popular software for simulation of physics processes in various areas. In spite of its primary application in high-energy particle physics and astrophysics, it is also widely used for studies in space and medical science. The accuracy of Geant4 simulations depends on the credibility of both models of physics processes and the description of materials involved in simulations. In this work, model of rough isotropic optical surfaces is extended to Geant4 providing with the knowledge of their in-plane BRDF scatter profile. We updated Geant4’s algorithm responsible for tracking photon on a boundary of two optical environments to reflect the scatter profile of isotropic optical surfaces. To examine reliability of models, we measured BRDF profile of Tyvek, mylar and glass mirror samples by means of CASI measurement systems. We used obtained BRDF profile to setup optical properties of model counterpart of measured samples. Then we compared scattered profile in simulation with real one.

The southern Pierre Auger Observatory has been detecting cosmic rays above 1018eV since 2004, exploiting a hybrid air shower detection technique, with 1660 water Cherenkov detectors together with 24 air fluorescence telescopes on a 3000 km2 site. As low energy enhancements to the observatory, 3 additional telescopes with elevated fields of view were built (HEAT). The detector density was increased in the HEAT fields of view by a factor of four in an area of about 25 km2. This setup enables unbiased hybrid data taking above 1017eV. The infilled area is also being equipped with large underground scintillator muon detectors (AMIGA). Finally, a prototype array of radio antenna stations (AERA), working from 30 to 80 MHz, has been installed in a part of the infill. Properties and status of AMIGA, HEAT, and AERA are presented.

The aim of the AIRFLY (air fluorescence yield) project is to simulate and to measure the process of the fluorescence and Cherenkov emission produced by impact of cosmic rays on molecules of nitrogen in high level atmosphere. Several setups were designed to measure fluorescent and Cherenkov light. We report the chamber with controlled atmosphere to simulate conditions in various levels of the Earth atmosphere. The chamber was designed in the Institute of Physics of Academy of Sciences of the Czech Republic in cooperation with the Faculty of Mechanical Engineering, Czech Technical University and the Joint Laboratory of Optics of Palacky University and Institute of Physics of Academy of Sciences in Olomouc.

We have used our experience in the production of ultralight glass mirrors for the realization of a segmented LIDAR mirror. For non-imaging type of LIDAR, which is meant for monitoring of optical properties of the atmosphere, we designed tessellated mirror from nine segments. The diameter of the whole mirrors system is 1000 mm.

Air fluorescence yield is defined as the number of photons, produced by a charged particle, per meter of travel in the air. The excited molecules emit light in the near UV and in the visible region between 300 nm and 400 nm. We describe the simple light collection system for analysis of the faint signal.

The fluorescence detector, a component of the AUGER project, is designed to observe fluorescent light generated in interactions of high energy cosmic rays with nitrogen atoms in the Earth's atmosphere. This article present several designs of optical filters transmitting in the range 300 nm- 420 nm, where the fluorescent light is emitted. Two approaches are proposed: a system of thin dielectric layers and a combination of suitable glass plate. Quality of different filters is determined according to the value of transmittance in the required wavelength range, the shape of the transmittance curve at the edge of the transmitting window, long-term stability as well as feasibility and cost of their mass production. Selected types of filters were prepared, their parameters measured and compared with predicted values.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Diffuse and specular characteristics of the Tyvek 1025-BL material are reported with respect to their implementation in the Geant4 Monte Carlo simulation toolkit. This toolkit incorporates the UNIFIED model. Coefficients defined by the UNIFIED model were calculated from the bidirectional reflectance distribution function (BRDF) profiles measured with a scatterometer for several angles of incidence. Results were amended with profile measurements made by a profilometer.

Joint Laboratory of Optics produce mirrors for fluorescence optical detector of the Pierre Auger Project placed in Argentina. We want resume our manufacturing quality measurements and compare first two made telescopes with the prototype one. We measure radius of curvature, spot size and reflectivity in ultra-violet region.

We describe an unusual optical layout of the fluorescence detector telescope what is a part of the Pierre Auger observatory. The fluorescence detector is a very fast telescope with the relative aperture fno ~ 0.77 and the large field of view 30 × 30 degrees. The primary objective for the Auger fluorescence telescope is to measure accurately the longitudinal development profiles of air showers of the cosmic rays above 10 EeV energy.

The next generation of Cherenkov telescope cameras feature Silicon Photo Multipliers (SiPM), which can guarantee excellent performance and allow for observation also under moonlight, increasing duty-cycle and therefore the physics reach. A 4 m-diameter Davies-Cotton prototype telescope with a 9-degree optical FoV and a 1296-pixel SiPM camera, has been designed to meet the requirements of the next generation of ground-based gamma-ray observatories at the highest energies. The large-scale production of the telescopes for array deployment has required the development of a fully automated calibration strategy which relies on a dedicated hardware, the Camera Test Setup (CTS). For each camera pixel, the CTS is equipped with two LEDs, one operated in pulsed mode to reproduce signal and one in continuous mode to reproduce night-sky background. In this contribution we will present the camera calibration strategy, from the laboratory measurement to the on-site monitoring with emphasis on the results obtained with the first camera prototype. In addition, key performances such as charge resolution, time resolution and trigger efficiencies and their degradation with increasing night-sky background level will be presented., PoS: Proceedings of Science, 358, ISSN:1824-8039, Proceedings of 36th International Cosmic Ray Conference (ICRC 2019)

The Fluorescence detector Array of Single-pixel Telescopes (FAST) is a design concept for the next generation of ultrahigh-energy cosmic ray (UHECR) observatories, addressing the requirements for a large-area, low-cost detector suitable for measuring the properties of the highest en- ergy cosmic rays. In the FAST design, a large field of view is covered by a few pixels at the focal plane of a mirror or Fresnel lens. Motivated by the successful detection of UHECRs using a prototype comprised of a single 200 mm photomultiplier-tube and a 1 m^2 Fresnel lens system [Astropart.Phys. 74 (2016) 64-72], we have developed a new full-scale prototype consisting of four 200 mm photomultiplier-tubes at the focus of a segmented mirror of 1.6 m in diameter. In October 2016 we installed the full-scale prototype at the Telescope Array site in central Utah, USA, and began steady data taking. We report on first results of the full-scale FAST prototype, including measurements of artificial light sources, distant ultraviolet lasers, and UHECRs.