Lithuanian scientific research – on the cover of a prestigious magazine: developed and tested a new generation of optical lenses | Business


From the article entitled “Light Engineering and Silicon Diffractive Optics Assisted Nonparaxial Terahertz Imaging” (lit. “Light engineering and silicon diffraction optics for non-paraxial terahertz imaging”), lead author – FTMC Fundamental Research Department researcher Dr. Sergey Orlov.

The cover illustration of the magazine was created (and she is one of the authors of the article) by Dr. Dr. Rusnė Ivaškevičiūtė-Povilauskienė.

FTMC photo/Rusnė Ivaškevičiūtė-Povilauskienė

What do we see here?

“My colleagues and I joke that we could compare our achievement to being on the cover of Cosmopolitan,” Rusnė smiles. – Laser & Photonics Reviews is a prestigious journal with a very high citation rate, which is great fun.

The editors of the magazine itself offered us to create a cover based on our article. It happens that several groups of scientists send their versions, and the editors choose a winner.”

“Usually, the works that the editors of those magazines consider to be exceptional end up on the cover,” Sergej observes. – In our case, we have seen from the beginning that this article is one of the editors’ favorites. When we sent the revised version, we received a response in record time – within a few hours – that the article had been accepted into the journal.”

Photo by Marius Linauskas/Sergejus Orlovas

What’s on the cover? These are four optical elements, silicon-created (and laser-etched) lenses, each of which uniquely forms the radiation of terahertz light invisible to the naked eye. The scientific work was aimed at comparing the effectiveness of these elements: theoretical physicists of the Fundamental Research Department of FTMC engaged in calculations, scientists of the Coherent Optics Laboratory of this department produced lenses, and then the specialists of the Optoelectronics Department conducted experiments with them.

Let’s examine R. Ivaškevičiūtė-Povilauskienė’s illustration more closely.

At the very top is the so-called Airy lens, which is characterized by the fact that the terahertz light passing through it is able to restore itself, even when it encounters an obstacle. In other words, such a bent light beam allows you to study and observe specimens “around the corner”.

Publisher's photo/Magazine cover

Publisher’s photo/Magazine cover

By the way, this was one of the topics in Rusnė’s recently defended doctoral thesis. Airy’s lens research has already received international attention: she and her colleagues published an article in the prestigious Nature group journal Light: Science & Applications. “And the funnest thing is to tell people about it – because they are immediately “hooked”: how is it possible to see things “around the corner”?”, the physicist recalls.

What do we see below? The first from the left is a Fresnel lens that focuses the terahertz image to a single point; in the middle we find the Bessel lens: it forms a straight, long needle-shaped beam of light, so it allows a fairly bright image to be seen in the deeper layers of the sample; while on the right is a Fibonacci lens that is able to focus light to two different points at the same time!

All of these optical elements, as clearly illustrated on the cover, can be useful in one way or another to scientists testing the possibilities of terahertz imaging.

The science and art of a single pixel

The main author of the article is dr. Sergey Orlov explains in more detail about the essence of this research. In order to better understand experiments with terahertz light, let’s remember a much more common activity for each of us – photography:

“People who do photography professionally use cameras. It uses lenses or lens systems inside the lens that project an image made up of millions of pixels onto a dedicated matrix. It’s called one-shot imaging: you aim, you shoot, and you get a picture.”

According to the scientist, there are certain laws that indicate at what distance the photographed object should be from the lens of the photo lens, and also at what distance from the lens the pixel matrix of the camera should be. Sometimes you have to rotate the lens – zoom in or out – to get sharp and contrasty images.

“The problem with terahertz imaging is that it’s difficult and expensive to build something like a camera in this wavelength range of light. Therefore, another concept is used – single pixel representation. Various tricks are used to make one image out of many one-pixel images,” says S. Orlovas.

At FTMC’s Optoelectronics Department, objects illuminated by terahertz light are imaged using so-called raster scanning. What is it? A small sensor slowly moves across the sample and registers an image on the computer by “reacting” to the terahertz waves reflected back. The sensor collects information from each scanned pixel, and all these individual dots are finally combined into a single image of the object. It’s like using a flashlight in a dark room and moving it around to see different parts of the room.

“In principle, the work is about such a methodology, only we raised the question of whether it exists in such a representation, as a colleague prof. Gintaras Valušis joked, “Orlov’s laws” help to determine the positions where the pixel, sensor, object should be and with what light that object should be illuminated.

We have already established that it is not necessary to use only standard optical lenses for single-pixel imaging. It turns out that exotic elements that people don’t use in “one-shot” imaging can also be suitable here – and these are non-standard Airy, Fresnel, Bessel and Fibonacci lenses,” Sergejus says.

Thus, the authors of the article raised the question of whether it is possible to use these elements qualitatively for experiments with terahertz light.

“To our surprise, it turned out that we could do it. We managed to digitally assess ourselves and experimentally confirm which combination of illuminating and light-collecting elements ensures the best image contrast, resolution and depth of field,” says the physicist.

You can get acquainted with the scientific article of the FTMC team by clicking on this link.

The article is in Lithuanian

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