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THz spectroscopy has reached imaging capability with a spatial resolution of a few micrometres. This property enables measurements and imaging of biological samples like cells. THz photons have very low photon energies in the…

In part I we introduced modified Landweber-Kaczmarz methods and have established a convergence analysis. In the present work we investigate three applications: an inverse problem related to thermoacoustic tomography, a nonlinear inverse…

Numerical Analysis · Mathematics 2020-11-20 M. Haltmeier , R. Kowar , A. Leitao , O. Scherzer

Thermal tomography is an imaging technique for deducing information about the internal structure of a physical body from temperature measurements on its boundary. This work considers time-dependent thermal tomography modeled by a parabolic…

Numerical Analysis · Mathematics 2017-07-25 Nuutti Hyvönen , Lauri Mustonen

The purpose of this report is a study of the algebraic approach possibilities to reconstruct images. This approach is reduced to solution of the large system of linear algebraic equations. We also point out some possible further…

General Physics · Physics 2016-01-01 E. E. Libin , S. V. Chakhlov , D. Trinca

In this paper, the problem of terahertz pulsed imaging and reconstruction is addressed. It is assumed that an incomplete (subsampled) three dimensional THz data set has been acquired and the aim is to recover all missing samples. A…

Computer Vision and Pattern Recognition · Computer Science 2015-06-17 Vahid Abolghasemi , Hao Shen , Yaochun Shen , Lu Gan

We study an inverse boundary value problem for the nonlinear wave equation in $2 + 1$ dimensions. The objective is to recover an unknown potential $q(x, t)$ from the associated Dirichlet-to-Neumann map using real-valued waves. We propose a…

Numerical Analysis · Mathematics 2025-11-18 Markus Harju , Suvi Anttila , Teemu Tyni

Measuring terahertz waveforms in terahertz spectroscopy often relies on electrooptic sampling employing a ZnTe crystal. Although the nonlinearities in such zincblende semiconductors induced by intense terahertz pulses have been studied at…

Terahertz microscopy has attracted attention owing to distinctive characteristics of the THz frequency region, particularly non-ionizing photon energy, spectral fingerprint, and transparency to most nonpolar materials. Nevertheless, the…

Tomographic investigations are a central tool in medical applications, allowing doctors to image the interior of patients. The corresponding measurement process is commonly modeled by the Radon transform. In practice, the solution of the…

Numerical Analysis · Mathematics 2025-10-17 Richard Huber

Compact terahertz (THz) functional devices are greatly sought after for high-speed wireless communication, biochemical sensing, and non-destructive inspection. However, conventional devices to generate and guide THz waves are afflicted with…

Terahertz single-pixel imaging (THz SPI) has garnered widespread attention for its potential to overcome challenges associated with THz focal plane arrays. However, the inherently long wavelength of THz waves limits imaging resolution,…

Image and Video Processing · Electrical Eng. & Systems 2025-08-05 Yongsheng Zhu , Shaojing Liu , Ximiao Wang , Runli Li , Haili Yang , Jiali Wang , Hongjia Zhu , Yanlin Ke , Ningsheng Xu , Huanjun Chen , Shaozhi Deng

Terahertz (THz) communication is a promising technology for future wireless communications, offering data rates of up to several terabits-per-second (Tbps). However, the range of THz band communications is often limited by high pathloss and…

Signal Processing · Electrical Eng. & Systems 2024-01-29 Muddasir Rahim , Thanh Luan Nguyen , Georges Kaddoum , Tri Nhu Do

Deformable image registration is a standard engineering problem used to determine the distortion experienced by a body by comparing two images of it in different states. This study introduces two new DIR methods designed to capture…

Computer Vision and Pattern Recognition · Computer Science 2024-09-04 Daniel E. Hurtado , Axel Osses , Rodrigo Quezada

While it is well known that X-ray tomography using a polychromatic source is non-linear, as the linear attenuation coefficient depends on the wavelength of the X-rays, tomography using near monochromatic sources are usually assumed to be a…

Instrumentation and Detectors · Physics 2017-05-16 William R. B. Lionheart , Bjørn Tore Hjertaker , Rachid Maad , Ilker Meric , Sophia B. Coban , Geir Anton Johansen

We propose a variational regularisation approach for the problem of template-based image reconstruction from indirect, noisy measurements as given, for instance, in X-ray computed tomography. An image is reconstructed from such measurements…

Optimization and Control · Mathematics 2019-04-02 Lukas F. Lang , Sebastian Neumayer , Ozan Öktem , Carola-Bibiane Schönlieb

We report on the nonlinear spectroscopy of water vapor at THz frequencies. Atmospheric water vapor has a rich spectrum with several strong resonances at frequencies below 3 THz, falling within the range of operation of most existing THz…

A basic aim of ongoing and upcoming cosmological surveys is to unravel the mystery of dark energy. In the absence of a compelling theory to test, a natural approach is to better characterize the properties of dark energy in search of clues…

Cosmology and Nongalactic Astrophysics · Physics 2010-11-11 Tracy Holsclaw , Ujjaini Alam , Bruno Sanso , Herbert Lee , Katrin Heitmann , Salman Habib , David Higdon

A new approach is proposed for reconstruction of images from Radon projections. Based on Fourier expansions in orthogonal polynomials of two and three variables, instead of Fourier transforms, the approach provides a new algorithm for the…

Classical Analysis and ODEs · Mathematics 2007-05-23 Yuan Xu

Lightwave-driven terahertz scanning tunnelling microscopy (THz-STM) is capable of exploring ultrafast dynamics across a wide range of materials with angstrom resolution. In contrast to scanning near-field optical microscopy, where photons…

Mesoscale and Nanoscale Physics · Physics 2024-11-14 Vedran Jelic , Stefanie Adams , Mohamed Hassan , Kaedon Cleland-Host , S. Eve Ammerman , Tyler L. Cocker

Terahertz radiation enables non destructive, depthresolved analysis of layered artworks. This study demonstrates THz multispectral imaging ability to reveal concealed text beneath mockup of pictorial layers, reconstructing hidden narratives…