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12 pages, 7794 KiB

Open AccessArticle

Single-Shot Direct Transmission Terahertz Imaging Based on Intense Broadband Terahertz Radiation

by Zhang Yue, Xiaoyu Peng, Guangyuan Li, Yilei Zhou, Yezi Pu and Yuhui Zhang

Sensors 2024, 24(13), 4160; https://doi.org/10.3390/s24134160 - 26 Jun 2024

Cited by 3 | Viewed by 1993

There are numerous applications of terahertz (THz) imaging in many fields. However, current THz imaging is generally based on scanning technique due to the limited intensity of the THz sources. Thus, it takes a long time to obtain a frame image of the target and cannot meet the requirement of fast THz imaging. Here, we demonstrate a single-shot direct THz imaging strategy based on a broadband intense THz source with a frequency range of 0.1~23 THz and a THz camera with a frequency response range of 1~7 THz. This THz source was generated from the laser–plasma interaction, with its central frequency at ~12 THz. The frame rate of this imaging system was 8.5 frames per second. The imaging resolution reached 146.2 μm. With this imaging system, a single-shot THz image for a target object with a size of more than 7 cm was routinely obtained, showing a potential application for fast THz imaging. Furthermore, we proposed and tested an image enhancement algorithm based on an improved dark channel prior (DCP) theory and multi-scale retinex (MSR) theory to optimize the image brightness, contrast, entropy and peak signal-to-noise ratio (PSNR). Full article

(This article belongs to the Special Issue Terahertz Spectroscopic Sensing and Imaging Technology for Biomedicine)

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10 pages, 5302 KiB

Open AccessArticle

Resonant Excitation of the Ferroelectric Soft Mode by a Narrow-Band THz Pulse

by Kirill Brekhov, Vladislav Bilyk, Andrey Ovchinnikov, Oleg Chefonov, Vladimir Mukhortov and Elena Mishina

Nanomaterials 2023, 13(13), 1961; https://doi.org/10.3390/nano13131961 - 28 Jun 2023

Cited by 4 | Viewed by 1685

Abstract

This study investigates the impact of narrow-band terahertz pulses on the ferroelectric order parameter in Ba_0.8Sr_0.2TiO₃ films on various substrates. THz radiation in the range of 1–2 THz with the pulse width of about 0.15 THz was separated from a broadband pulse with the interference technique. The 375 nm thick BST film on a MgO (001) substrate exhibits enhanced THz-induced second harmonic generation when excited by THz pulses with a central frequency of 1.6 THz, due to the resonant excitation of the soft phonon mode. Conversely, the BST film on a Si (001) substrate shows no enhancement, due to its polycrystalline state. The 800 nm thick BST film on a MgO (111) substrate demonstrates the maximum of a second harmonic generation signal when excited by THz pulses at 1.8 THz, which is close to the soft mode frequency for the (111) orientation. Notably, the frequency spectrum of the BST/MgO (111) film reveals peaks at both the fundamental and doubled frequencies, and their intensities depend, respectively, linearly and quadratically on the THz pulse electric field strength. Full article

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8 pages, 2234 KiB

Open AccessCommunication

Backward THz Emission from Two-Color Laser Field-Induced Air Plasma Filament

by Yuxuan Chen, Yuhang He, Liyuan Liu, Zhen Tian, Jianming Dai and Xi-Cheng Zhang

Sensors 2023, 23(10), 4630; https://doi.org/10.3390/s23104630 - 10 May 2023

Cited by 4 | Viewed by 2722

Abstract

Two-color laser field-induced plasma filaments are efficient broadband terahertz (THz) sources with intense THz waves emitted mainly in the forward direction, and they have been investigated intensively. However, investigations on the backward emission from such THz sources are rather rare. In this paper, we theoretically and experimentally investigate the backward THz wave radiation from a two-color laser field-induced plasma filament. In theory, a linear dipole array model predicts that the proportion of the backward emitted THz wave decreases with the length of the plasma filament. In our experiment, we obtain the typical waveform and spectrum of the backward THz radiation from a plasma with a length of about 5 mm. The dependence of the peak THz electric field on the pump laser pulse energy indicates that the THz generation processes of the forward and backward THz waves are essentially the same. As the laser pulse energy changes, there is a peak timing shift in the THz waveform, implying a plasma position change caused by the nonlinear-focusing effect. Our demonstration may find applications in THz imaging and remote sensing. This work also contributes to a better understanding of the THz emission process from two-color laser-induced plasma filaments. Full article

(This article belongs to the Special Issue Terahertz Imaging, Sensing and Communications Technologies)

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14 pages, 2146 KiB

Open AccessArticle

Sensitivity of Neuroblastoma and Induced Neural Progenitor Cells to High-Intensity THz Radiation

by Dmitry Sitnikov, Veronika Revkova, Inna Ilina, Rimma Shatalova, Pavel Komarov, Evgenia Struleva, Mikhail Konoplyannikov, Vladimir Kalsin and Vladimir Baklaushev

Int. J. Mol. Sci. 2023, 24(7), 6558; https://doi.org/10.3390/ijms24076558 - 31 Mar 2023

Cited by 6 | Viewed by 2771

Abstract

THz radiation induces a variety of processes in cells and has attracted the attention of researchers in recent decades. Here, data on the effects of high-intensity terahertz (THz) radiation on human directly reprogrammed neural progenitor cells (drNPCs) and on neuroblastoma cells (SK-N-BE (2)) were obtained for the first time. The results demonstrated that the exposure of non-tumor and tumor cells to broadband (0.1–3 THz) THz pulses with the intensity of 21 GW/cm² and the electric field strength of 2.8 MV/cm for 30 min induced neither a noticeable genotoxic effect nor a statistically significant change in the proliferative activity and cell differentiation. It was also shown that the combined effect of THz radiation and salinomycin, a promising antitumor agent, on neuroblastoma cells did not enhance the genotoxic effect of this antibiotic. However, further studies involving chemotherapy drugs and other exposure parameters are warranted to introduce this new concept into anti-tumor clinical practice and to enhance the efficacy of the existing approaches. Full article

(This article belongs to the Special Issue Molecular Research on Neuroblastoma: Current Status and Future Perspectives)

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13 pages, 3836 KiB

Open AccessFeature PaperArticle

Performance Evaluation of a THz Pulsed Imaging System: Point Spread Function, Broadband THz Beam Visualization and Image Reconstruction

by Marta Di Fabrizio, Annalisa D’Arco, Sen Mou, Luigi Palumbo, Massimo Petrarca and Stefano Lupi

Appl. Sci. 2021, 11(2), 562; https://doi.org/10.3390/app11020562 - 8 Jan 2021

Cited by 23 | Viewed by 4492

Abstract

Terahertz (THz) technology is a promising research field for various applications in basic science and technology. In particular, THz imaging is a new field in imaging science, where theories, mathematical models and techniques for describing and assessing THz images have not completely matured yet. In this work, we investigate the performances of a broadband pulsed THz imaging system (0.2–2.5 THz). We characterize our broadband THz beam, emitted from a photoconductive antenna (PCA), and estimate its point spread function (PSF) and the corresponding spatial resolution. We provide the first, to our knowledge, 3D beam profile of THz radiation emitted from a PCA, along its propagation axis, without the using of THz cameras or profilers, showing the beam spatial intensity distribution. Finally, we evaluate the THz image formation on a test-sample composed by a regular linen natural pattern. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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10 pages, 19246 KiB

Open AccessArticle

Broadband Anisotropic Optical Properties of the Terahertz Generator HMQ-TMS Organic Crystal

by Annalisa D’Arco, Luca Tomarchio, Valerio Dolci, Paola Di Pietro, Andrea Perucchi, Sen Mou, Massimo Petrarca and Stefano Lupi

Condens. Matter 2020, 5(3), 47; https://doi.org/10.3390/condmat5030047 - 14 Jul 2020

Cited by 16 | Viewed by 4635

Abstract

HMQ-TMS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate) is a recently discovered anisotropic organic crystal that can be exploited for the production of broadband high-intensity terahertz (THz) radiation through the optical rectification (OR) technique. HMQ-TMS plays a central role in THz technology due to its broad transparency range, large electro-optic coefficient and coherence length, and excellent crystal properties. However, its anisotropic optical properties have not been deeply researched yet. Here, from polarized reflectance and transmittance measurements along the

x_{1}

and

x_{3}

axes of a HMQ-TMS single-crystal, we extract both the refraction index n and the extinction coefficient k between 50 and 35,000 cm

^{- 1}

. We further measure the THz radiation generated by optical rectification at different infrared (IR) wavelengths and along the two

x_{1}

and

x_{3}

axes. These data highlight the remarkable anisotropic linear and nonlinear optical behavior of HMQ-TMS crystals, expanding the knowledge of its properties and applications from the THz to the UV region. Full article

(This article belongs to the Special Issue THz: Research Frontiers for New Sources, Imaging and Other Advanced Technologies)

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