FAST telescopes have opened the way to the emergence of observatories with hundreds of individual telescopes

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It is not a common thing that a new telescope for detecting cosmic rays is introduced to the world. The feat of our colleagues from the Joint Laboratory of Optics in Olomouc can thus be seen as unique. Their new fluorescence FAST (Fluorescence Detector Array of Single-pixel Telescopes) telescope is really compact, can be loaded into a container, shipped to the final site and installed there. It is also fully equipped with a photovoltaic system including batteries, so it does not require an established power infrastructure. In addition, it is significantly cheaper than competing systems. More information about the telescope and other projects at the Joint Laboratory of Optics in Olomouc was provided by Dušan Mandát.

Last summer, the inauguration of the new FAST telescope took place in Olomouc, which also Dr. Schovánek from the Joint Laboratory of Optics spoke about it in an interview. I am glad that it can be an opening point of our interview. You are one of its authors – how do you see its use?

The idea is to build a huge observatory, which should reduce the cost of one detector in a fundamental way. In the FAST project we are talking about an area of 150,000 km2, which is really hundreds of telescopes of this type. But this means that we need to reduce the price so that we can cover everything with a reasonable grant. Such an observatory would work in a slightly different way from the Pierre Auger Observatory, because a large area would be covered. The telescopes would just exchange the times when a signal was detected, and since the probability of detecting high-energy particles is small, we expect to detect perhaps dozens of such particles per year.

Whose idea was it to come up with this new type of fluorescence telescope?

As part of the Pierre Auger Observatory upgrade, Professor Paulo Privitera proposed this as a general concept to simplify the detector. Everything was based on calculations so that the background night sky would not interfere with the detected signal. The project was first taken up by the Japanese, who wanted to use a Fresnel lens. From the Czech team, it was Miroslav Palatka who first got involved in the project, but he did not agree with the Japanese method. We did some measurements, calculations and simulations to show them that their model would not work. Miroslav Palatka then came up with the idea of using the mirror telescope concept, which successfully passed all the tests. So, this is how we came into the limelight and I would already dare to say that we are the leaders of the whole project.

How does this telescope work?

The telescope works similarly to standard fluorescence telescopes (Pierre Auger Observatory, Telescope Array experiment), i.e. it displays the fluorescence signal generated by a shower of secondary particles in the atmosphere on a camera in the image plane of the telescope. The fluorescence telescope camera signals are then used to reconstruct the energy and direction of the primary particle impact. Existing observatories also use a network of ground-based detectors for the reconstruction. In the case of the FAST project, we will work only with fluorescence telescopes and "drive" the detection statistics by means a huge area with inexpensive telescopes.

What other projects are you involved in?

For example, we have made optics for CERN, and recently we have produced a fluorescence and Cherenkov telescope for EUSO-SPB2; the call for this project came directly from NASA. The idea was to make a helium high-altitude balloon that would take two telescopes to an altitude of about 20 kilometres. We made the two telescopes for them, but unfortunately, it didn't work out.
 The balloon went up, but there was a hole in it, so it crashed within a day and all the equipment got destroyed.

Are there any specifics about collaborating with NASA? Or was that your only project so far?

This has been our only project with NASA so far. They, of course, approached several different companies that produce optics, but it turned out that we were able to deliver the technology under conditions that no one else was able to. EUSO-SPB2 is a Pathfinder project for the future POEMMA orbital project.  It's extremely expensive to carry something up into space, not long ago it was $5,000 per kilogram. With what we can do, with glass optics, we won't get to a weight that is suitable for other potential projects, so we need to develop new technologies, like some composite mirrors using lightweight materials.

One last question: what are the mirrors of the future? Where is all this going? Will the new technologies be more environmentally friendly?

For imaging equipment, you have to have the exact shape of the mirror, which is why glass has been used for a very long time. Ceramics have also started to be used, but the process requires a lot of energy. For composite mirrors, only a thin layer of glass is used, which means that it is not as energy-intensive as casting a huge substrate. The Olomouc and Prague sections of the Division of Optics are working together to develop a 3D-printed structure that the glass would adhere well to, currently using 3D-printed titanium. Considering the environment, glass is an ideal recyclable raw material. What we use, for example, in the Cherenkov Telescope Array project, is aluminium, glass, and glue. Aluminium is recyclable, glass is recyclable. On the other hand, the Chinese are pushing it quite far, using 3D printing for plastic lenses, so it's possible that in the near future we will be making plastic composite mirrors.  Or we'll send a printer to orbit that will print everything right there. Who knows?