Scientists find simple method to enhance responsivity of terahertz radiation detectors by 3.5 folds

 

https://www.eurekalert.org/pub_releases/2021-06/tpu-sfs062421.php

Scientists of Tomsk Polytechnic University jointly with colleagues from Spanish universities have offered a simple method how to enhance the responsivity of terahertz radiation detectors by 3.5 folds using a small Teflon cube. The 1 mm cube must be put on the surface of the detector without changing the inner design of the detector.

Such detectors are applied, for instance, in a full-body scanner, spectrometer, in medical devices for diagnosing skin cancer, burn injuries, pathological changes in blood. The research findings are published in the Optics Letters academic journal (IF: 3,714; Q1).

Terahertz range lies between microwave and infrared ranges in the electromagnetic spectrum. Waves shorter than 1 mm refer to the terahertz range. Their feature lies in that they are capable to percolate various materials and at the same time, they do not lead to atomic ionization of matter alternatively to X-rays.

"Terahertz radiation detectors are, as a rule, rather compact devices. Nowadays, researchers from different countries are interested in the enhancement of their responsivity and other parameters. The higher responsivity, the weaker signals can be received and more precise measurements can be carried out. Most researchers are trying to solve this problem by changing the design of the detector and the materials it is made from. It is complicated and often very expensive. Meanwhile, our solution is plain to see," Oleg Minin, Professor of the Division for Electronic Engineering of the TPU School of Non-Destructive Testing, one of the authors of the article, says.

In their experiments, the scientists used a microparticle in the form of the Teflon cube, an available dielectric material through which electromagnetic waves of the terahertz range are capable to percolate. The cube was put on the surface of the detector.

"There is a responsive site inside of the detector. The site can be made from various materials but its typical scale is always less than the wavelength. It is the area responsible for trapping electromagnetic waves and transferring them. Due to the form and material, our cube possesses a capability to focalize radiation well, falling on the responsive site of the detector, in the scale limited to or smaller than a diffraction-limited system. The experiments conducted jointly with the Spanish colleagues proved it: the particle focalized the radiation and the emitted radiation fell into the responsive area," Oleg Minin explains.

According to the scientists, the developed method of detector responsivity enhancement without changing its design is applied to almost any detectors of various ranges.

During the experiments, the scientists fixed responsivity enhancement by 11 decibels, which is 3.5 folds higher than the standard parameters of the detector.

The researchers from University of Salamanca (Spain), Polytechnic University of Valencia (Spain), Institute of High-Pressure Physics of the Polish Academy of Sciences (Poland) and Imperial College London (England) took part in the research. The research was conducted with the support of the TPU Competitiveness Enhancement Program.

Scientists verify a way of how to improve resolution of most powerful microscopes

Simulated near-field E 2 field enhancement distribution on xz plane with the amplitude mask apodization. Credit: Tomsk Polytechnic University
 https://phys.org/news/2018-04-scientists-resolution-powerful-microscopes.html#jCp

Researchers from Tomsk Polytechnic University (Russia) and Bangor University (UK) have experimentally verified anomalous amplitude apodization for non-spherical particles for the first time. This phenomenon makes it possible to boost the magnifying power of microscopes and to record molecules and viruses more effectively. The study results were reported in Journal of Infrared, Millimeter, and Terahertz Waves.

"If we mask part of an ordinary lens surface with an optical filter, it will increase the magnifying power of the lens. But peak field intensity drops dramatically. The same effect is typical of spherical particle-lenses in nanoscopes or high-definition optical microscopes with a magnifying power of 50 nanometers. If we use non-spherical particles, including cylinders with illuminated butt-ends, as lenses, and if we mask part of the surface, it will simultaneously boost their magnifying power and peak field intensity. This is called the amplitude mask apodization effect," Professor Igor Minin from Tomsk Polytechnic University's faculty of electronic engineering noted.

Non-spherical particles function as super-lenses accumulating evanescent (damp) waves that can form an image with unprecedentedly high definition levels.

In their work, scientists cite experimental data confirming the existence of the amplitude mask apodization effect in the millimeter waveband. During their experiments, cuboid dielectric particles, part of whose surfaces (about 45 percent) are covered with a copper amplitude mask, showed a 36-percent increase in magnifying power, with peak field intensity levels increasing by over 30 percent.

You could say that spherical particle-lenses boost the magnifying power of nano-scopes only through the loss of energy. But when we use non-spherical particles, the magnifying power increases at a rate commensurate with the greater peak field intensity levels," Minin added.The long-term development of this technique will make it possible to obtain images of large biological molecules, viruses and the internal elements of living cells using non-spherical particles.

Experts will no longer have to painstakingly prepare various samples. For example, this is an important aspect of fluorescent microscopy. The amplitude mask apodization effect has a wide range of applications where sub-wavelength focusing is required. These are medicine, non-destructive testing, flaw detection, on chip processing and data transfer systems, etc.