Neural-network based approach to optimize THz computer generated holograms

Terahertz (THz) optics often encounters the problem of small f number values (elements have relatively small diameters comparing to focal lengths). The need to redirect the THz beam out of the optical axis or form particular intensity distributions resulted in the application of iterative holographic methods to design THz diffractive elements. Elements working on-axis do not encounter significant improvement while using iterative holographic methods, however, for more complicated distributions the difference becomes meaningful. Here, we propose a totally different approach to design THz holograms, utilizing a neural network based algorithm, suitable also for complicated distributions. Full Text: PDF ReferencesY. Tao, A. Fitzgerald and V. Wallace, "Non-Contact, Non-Destructive Testing in Various Industrial Sectors with Terahertz Technology", Sensors, 20(3), 712 (2020). CrossRef J. O'Hara, S. Ekin, W. Choi and I. Song, "A Perspective on Terahertz Next-Generation Wireless Communications", Technologies, 7(2), 43 (2019). CrossRef L. Yu et al., "The medical application of terahertz technology in non-invasive detection of cells and tissues: opportunities and challenges", RSC Advances, 9(17), 9354 (2019). CrossRef A. Siemion, "The Magic of Optics—An Overview of Recent Advanced Terahertz Diffractive Optical Elements", Sensors, 21(1), 100 (2020). CrossRef A. Siemion, "Terahertz Diffractive Optics—Smart Control over Radiation", J. Infrared Millim. Terahertz Waves, 40(5), 477 (2019). CrossRef M. Surma, I. Ducin, P. Zagrajek and A. Siemion, "Sub-Terahertz Computer Generated Hologram with Two Image Planes", Appl. Sci., 9(4), 659 (2019). CrossRef S. Banerji and B.Sensale-Rodriguez, "A Computational Design Framework for Efficient, Fabrication Error-Tolerant, Planar THz Diffractive Optical Elements", Sci. Rep., 9(1), 5801 (2019). CrossRef J. Sun and F. Hu, "Three-dimensional printing technologies for terahertz applications: A review", Int. J. RF. Microw. C. E., 30(1) (2020). CrossRef E. Castro-Camus, M. Koch and A. I. Hernandez-Serrano, "Additive manufacture of photonic components for the terahertz band", J. Appl. Phys., 127(21), 210901 (2020). CrossRef https://community.wolfram.com/groups/-/m/t/2028026?p_%20479%20p_auth=blBtLb5d DirectLink P. Komorowski, et al., "Three-focal-spot terahertz diffractive optical element-iterative design and neural network approach", Opt. Express, 29(7), 11243-11253 (2021) CrossRef M. Sypek, "Light propagation in the Fresnel region. New numerical approach", Opt. Commun., 116(1-3), 43 (1995). CrossRef

The Application of Microplasma in the Terahertz Field: A Review

Terahertz functional devices are essential to the advanced applications of terahertz radiation in biology and medicine, nanomaterials, and wireless communications. Due to the small size and high plasma frequency of microplasma, the interaction between terahertz radiation and microplasma provides opportunities for developing functional terahertz devices based on microplasma. This paper reviews the applications of microplasma in terahertz sources, terahertz amplifiers, terahertz filters, and terahertz detectors. The prospects and challenges of the interdisciplinary research between microplasma and terahertz technology are discussed.

Distribution Characteristics of Ground Echo Amplitude and Recognition of Signal Grazing Angle

With the continuous advancement of electronic technology, terahertz technology has gradually been applied on radar. Since short wavelength causes severe ground clutter, this paper studies the amplitude distribution statistical characteristics of the terahertz radar clutter based on the measured data, and provides technical support for the radar clutter suppression. Clutter distribution is the function of the radar glancing angle. In order to achieve targeted suppression, in this paper, selected axial integral bispectrum (selected AIB) feature is selected as deep belief network (DBN)input to complete the radar glancing angle recognition and the network structure, network training method, robustness are analyzed also. The ground clutter amplitude distribution can follow normal distribution at 0~45° grazing angles. The Weibull distribution and G0 distribution can describe the amplitude probability density function of ground clutter at grazing angles 85° and 65°. The recognition rate of different signal grazing angles can reach 91% on three different terrains. At the same time, the wide applicability of the selected AIB feature is verified. The analysis results of ground clutter amplitude characteristics play an important role in the suppression of radar ground clutter.

THz Super-Resolution Imaging in Transmission Technology by Using Butterfly and Pattern Device Samples

Recently there has been an increasing demand for terahertz technology especially in imaging. In the past few decades, the applications of terahertz (THz) imaging technology have seen significant developments in the fields of biology, medical diagnosis, food safety, and nondestructive testing. The medical and semiconductor industry has always attracted significant attention worldwide. In particular, the importance of real and perfect inspection technologies has been growing due to an increasing demand for improving the quality of life and developing industries. This paper presents the research of THz technology with super-resolution THz imaging in transmission mode on four types of different samples. We have reported transmission measurement at different THz frequency of each sample. The butterfly sample used super-resolution THz imaging. The THz super-resolution is obtained excellent at 1.8 THz, it is near about 1 micrometer. A good resolution images have been obtained. This new THz super-resolution techniques can apply in medical and security purposes. Further applications will be reported in coming papers.

A Contactless Liquor Level Detection Method Using Terahertz Time-Domain Spectroscopy

In this paper, we proposed the terahertz technique to measure the liquid level of Chinese liquor in sealed pots. We analyzed the transmission process of terahertz pulse in the sealed pots and established a model of the relationship between terahertz pulse interval and liquor level. The measurement results are in good agreement with the theoretical model. The results show that the terahertz technique can realize the high precision measurement of liquor level. The absolute and relative errors are less than ±40 μm and 0.014%, respectively. In addition, we also evaluated the influence of dewdrop on the measurement accuracy. The results show that dewdrop only leads to a deviation of 18 μm. The results prove the value of terahertz technology in the field of liquid level monitoring.

A Review of THz Technologies for Rapid Sensing and Detection of Viruses including SARS-CoV-2

Virus epidemics such as Ebola virus, Zika virus, MERS-coronavirus, and others have wreaked havoc on humanity in the last decade. In addition, a coronavirus (SARS-CoV-2) pandemic and its continuously evolving mutants have become so deadly that they have forced the entire technical advancement of healthcare into peril. Traditional ways of detecting these viruses have been successful to some extent, but they are costly, time-consuming, and require specialized human resources. Terahertz-based biosensors have the potential to lead the way for low-cost, non-invasive, and rapid virus detection. This review explores the latest progresses in terahertz technology-based biosensors for the virus, viral particle, and antigen detection, as well as upcoming research directions in the field.

Terahertz absorption characteristics of guar gum determined via microfluidic technology

The vibrational energy levels of many biomolecules correspond to the terahertz band; thus, terahertz technology can be used to identify these substances. Moreover, as the biological activity of most biomolecules can be observed only in aqueous solution, the characteristics of such biomolecules must be studied in aqueous solution. In this study, a simple microfluidic chip, a temperature control device and a strong electric field device were designed to study the terahertz absorption characteristics of guar gum for different temperatures, concentrations and electric field exposure durations, thus enabling the use of terahertz technology to analyse the characteristics of guar gum.