Tray Research Articles

Stacked Layers of Nb2O5/Pt/Nb2O5 Designed as Conducting Oxides, Terahertz Band Filters, and Semitransparent Light Absorbers

Stacked Layers of Nb2O5/Pt/Nb2O5 Designed as Conducting Oxides, Terahertz Band Filters, and Semitransparent Light Absorbers

Innovative Refractive Index Sensor Utilizing Terahertz Spectrum for Early Cancer Detection: a Photonic Crystal Fiber Approach.

In this article, we have presented a new cancer sensor with a square core Photonic Crystal Fiber (PCF) to detect the cancerous tissues of the cervix, breast, and skin. This process is thus streamlined and separated by PCF due to its excellent detection characteristics. All required configurations using the finite element method are developed, and various performances of the model are studied using MATLAB. The results depict a mathematical analysis regarding the effectiveness of the sensor within the frequency range of 1.0-2.8 THz. Its relative sensitivity becomes around 99.85% at 2.2 THz with 8.49 × 10-14 dB/m for CL. This PCF has a spot size 3.06 × 10-4 μm that further contributes an effective area of 9.078 × 10-8 m2. Moreover, it has a very small EML of 0.00182 cm-1. This device uses the unique photonic properties of cancer cells to provide quick, reliable, and really very accurate methods for cancer cell identification, such as in breast, cervical, and skin cancers. Due to small size and flexibility, only minimally invasive operations are possible. Real-time monitoring can also be provided, hence improving immediate evaluation and therapy efficacy. This article introduces a novel integration of PCF technology with THz radiation to create a highly sensitive sensor for early cancer detection. By utilizing THz waves' non-invasive and high-resolution properties, this sensor overcomes the sensitivity limitations of traditional methods. It also addresses scattering issues from conventional air hole shapes through optimized geometric configurations, setting a new standard in biomedical sensing and potentially revolutionizing early cancer diagnostics.

(Invited) Experimentally Measuring the Role of Ion-Phonon and Ion-Electron Correlations in Solid-State Li Ion Conductors

In superionic conductors, ion hopping involves a complex interplay of ion-phonon, ion-electron, and ion-ion correlations that is challenging to measure experimentally. In this presentation, we present a new experimental technique that can directly measure ultrafast ion hopping on its inherent picosecond and longer timescale. The technique works by measuring the time-resolved perturbation to a GHz impedance signal when potential ion-coupling interactions are driven with UV to THz irradiation. High-bandwidth, real-time electronics allow synchronization of the impedance measurement to ultrafast laser pulses for varying carrier frequencies. The result of the measurement is the relative strength of different correlations in the many-body ion hopping Hamiltonian. We demonstrate the technique on Li0.5La0.5TiO3 (LLTO) and single crystalline Li7La3Zr2O12 (LLZO), both solid-state Li+ conductors. The ultrafast laser-driven impedance measurements reveal that the dominant ion hopping mechanism in LLTO is through a coupled phonon-ion THz rocking mode. Although this higher frequency mode is less than one-quarter of the overall phonon density of states, it leads to the majority of ion hops as compared to other optical and acoustic phonon modes. Metastable states lasting tens of minutes were also measured for ion-electron perturbations. Further work on extending the technique to measure ion-ion correlations is currently underway. In general, the new technique applies to any complex ion conducting system such as polymers, fuel cells, supercapacitors, and membranes.

TCM combined with low radiation terahertz waves in the treatment of polycystic ovarian syndrome patients: Effects on plasma myocardial Nutrient-1

Polycystic ovary syndrome (PCOS) is a common endocrine disorder with abnormal cardiac trophy-1 (ANP) production and insulin resistance. In recent years, the application of low radioactive terahertz waves as a new therapeutic method in ovarian syndrome has attracted wide attention. The observation group received traditional Chinese medicine combined with low radiation terahertz wave treatment, and the control group received traditional treatment. Plasma ANP levels and insulin resistance indexes were compared between the two groups before and after treatment. The results showed that Chinese medicine combined with Western medicine had a good effect in the treatment of PCOS, which could effectively relieve symptoms, improve the levels of sex hormone, plasma cardiac fact-1 and insulin resistance, and did not increase adverse reactions compared with Western medicine alone, and could improve the pregnancy outcome, with good efficacy and safety. Terahertz waves are feasible in the detection of Chinese herbs. Traditional Chinese medicine combined with terahertz wave is a new choice for the treatment of PCOS, which is expected to be widely used in clinic.

Non-Thermal Effects of Terahertz Radiation on Gene Expression: Systematic Review and Meta-Analysis.

With the advancement of terahertz technology, unveiling the mysteries of terahertz has had a profound impact on the field of biomedicine. However, the lack of systematic comparisons for gene expression signatures may diminish the effectiveness and efficiency of identifying common mechanisms underlying terahertz effects across diverse research findings. We performed a comprehensive review and meta-analysis to compile patterns of gene expression profiles associated with THz radiation. Thorough bibliographic reviews were conducted, utilizing the PubMed, Embase, Web of Science, and ProQuest databases to extract references from published articles. Raw CEL files were obtained from Gene Expression Omnibus and preprocessed using Bioconductor packages. This systematic review (Registration No. CDR42024502937) resulted in a detailed analysis of 13 studies (14 papers). There are several possible mechanisms and pathways through which THz radiation could cause biological changes. While the established gene expression results are largely associated with immune response and inflammatory markers, other genes demonstrated transcriptional outcomes that may unravel unknown functions. The enrichment of genes primarily found networks associated with broader stress responses. Altogether, the findings showed that THz can induce a distinct transcriptomic profile that is not associated with a microthermal cellular response. However, it is impossible to pinpoint a single gene or family of genes that would accurately and reliably justify the patterns of gene expression response under THz exposure.

Carbon contrast agents for terahertz spectroscopic NDT of impacted glass fibre reinforced plastics

Impact damage poses a significant challenge for composite materials since it is often subsurface and hard to detect, necessitating effective assessment approaches. Traditional NDT methods face challenges in identifying this specific type of damage. In this study, a departure from traditional NDT approaches was taken by utilizing THz spectroscopy to detect impact damage. Three different lay-ups of GFRP laminates were studied; GFRP with non-woven carbon fibre veil, GFRP coated with MWCNTs, and plain GFRP. Impact tests were conducted ranging from 5, 12 and 20 J in energy and 2D images were then acquired It was found that the inclusion of the MWCNTs and carbon veil gave superior image contrast compared to plain GFRP. Furthermore, the damaged area observed in the images increased with impact energy across all configurations. The outcomes derived from THz spectroscopy were benchmarked against those from ultrasound testing. THz spectroscopy demonstrates greater promise as a highly effective technique for detecting impact damage using carbon materials, offering advantages over traditional NDT methods due to its distinct wavelength, portability, non-contact capability, capacity to depict fibre alignment, lack of additional calibration specimens and coupling agents, and its ability to partially uncover the scope of impact damage.

Magnetic field enhanced terahertz generation from shape-dependent metallic nanoparticles

Abstract This communication deals with the analytical study of terahertz (THz) generation via frequency-difference mechanism using two circularly symmetric Gaussian laser beams with slightly different frequencies ω 1 and ω 2 and wave vectors k → 1 and k → 2 simultaneously propagating through a mixture of spatially corrugated noble-metal nanoparticles. The mixture, consisting of spherical nanoparticles (SNPs) and cylindrical nanoparticles (CNPs), is placed in a host medium under the influence of an externally applied static magnetic field. The two co-propagating laser beams impart a nonlinear ponderomotive force on the electrons of the NPs, causing them to experience nonlinear oscillatory velocity. Furthermore, the consequent nonlinear current density excites THz radiation at the beat frequency ω ( = ω 1 − ω 2 ) . Magnetic fields influence the surface plasmon resonance condition associated with electrons of the nanoparticles due to enhancement in ponderomotive nonlinearities, thereby causing an increment in the amplitude of the generated THz field. It is observed that the generated THz radiation has a strong dependence on the shape and size of the NPs in addition to the magnetic field strength. CNPSs provide greater THz amplitude than SNPs due to additional resonance modes, and combining both kinds of nanostructures further enhances the amplitude. THz radiation plays an important role in biomedical and pharmaceutical fields, communications, security and THz spectroscopy.

Broadband terahertz modulation in symmetric gate-controlled graphene photonic crystals

Innovative research in terahertz (THz) communications is urgently needed to meet the evolving demands of the industry. In the past, the absence of optoelectronic devices made it difficult to control THz waves effectively. In this study, a symmetric gate-controlled graphene photonic crystal (PC) is proposed, which achieves a modulation depth (MD) of more than 99 %, an ultralow insertion loss (IL) of 0.08, and a wide operation bandwidth (BW) simultaneously. Additionally, even in graphene samples with low carrier mobilities, the high-performance MD can be achieved with acceptable IL in the broadband THz range. Furthermore, our proposed one-dimensional graphene PC system enhances manufacturing convenience. Through the adoption of the proposed symmetric structure, highly efficient THz communications can be achieved through photonic systems that utilize graphene.

Unveiling enamel demineralization mechanisms by sensitive dielectric differentiation based on terahertz nanospectroscopy.

The early stage of dental caries, i.e. demineralization, has always been a topic of concern to dentists. Understanding the essential mechanism of its occurrence is of great significance for the prevention and treatment of dental caries. However, owing to limitations in resolution and the detection capabilities of diagnostic tools, the study of enamel demineralization has always been a challenge. Terahertz (THz) technology, especially the combination of scanning near-field optical microscopy (s-SNOM) and THz time-domain spectroscopy (TDS), due to its nanoscale resolution, has shown great advantages in the field of biological imaging. Here, a THz s-SNOM system is used to perform near-field imaging of enamel before and after demineralization at the nanoscale. It can be found that near-field signals decrease significantly after demineralization. This is due to the changes of the crystal lattice and the transfer of mineral ions during demineralization, which leads to a decrease in the permittivity of the enamel. The novel approach in this study reveals the essence of demineralization and lays the groundwork for additional research and potential interventions.

Integrated Couplers of THz Radiation for Helical Slow-Wave Structures.

We have designed an integrated device that couples input and output coaxial horn antennas with a self-assembled helical slow-wave structure cradled in a v-groove on a silicon-on-insulator wafer. These devices will potentially enable the characterization of cold parameters and beam-wave interaction in slow-wave structures on a wafer level, i.e., without having to dice and package individual devices. In addition, such vertically integrated antennas and helical slow-wave structures may form the basis of compact and low-cost traveling-wave tube amplifiers operating at THz frequencies.

Design Optimization of a THz Receiver Based on 60 nm Complementary Metal–Oxide–Semiconductor Technology

The technology transfer of terahertz wireless communication from research laboratories to commercial applications is a global strategic achievement currently pursued to match the ever-increasing demand for high-speed communication. The use of commercial integrated electronics for the detection of THz waves is an intriguing challenge which has enticed great interest in the scientific research community. Rapid progress in this field has led to the exploitation of THz direct detection using standard CMOS technology based on the so-called self-mixing effect. Our research, stemming out of a collaboration between Sapienza University of Rome and STMicroelectronics company, is focused on the complete design process of a THz rectifier, realized using 50 nm ST B55 CMOS technology. In this paper, we report the optimization process of a case-study receiver, aimed to demonstrate the feasibility of direct demodulation of the transmitted OOK signal. A relatively limited bandwidth extension is considered since the device will be included in a system adopting a radiation source with a limited band. The design refers to a specific technology, the 60 nm MOS in B55X ST; nevertheless, the proposed optimization procedure can be applied in principle to any MOS device. Several aspects of the rectification process and of the receiver design are investigated by combining different numerical simulation methodologies. The direct representation of the rectification effect through the equivalent circuit of the detector is provided, which allows for the investigation of the detector–amplifier coupling, and the computation of output noise equivalent power. Numerical results are presented and used as the basis for the optimization of the receiver parameters.

Design and optimization of hexagonal tungsten ring metasurface perfect absorbers with circuit model

In this paper, a perfect absorber (PA) based on tungsten is proposed to include hexagonal‐shaped metasurface absorbers with varying hole sizes ranging from quadrangular to circular, allowing them to cover a wide wavelength spectrum. The study investigates the effects of various parameters, including the number of sides of the inner hole, on the absorber's performance and identifies the most suitable absorber by introducing an equivalent circuit. The outcomes of full‐wave numerical simulations primarily based on the finite element method (FEM) highly correspond to the final results of the circuit model. Additionally, the circuit model significantly reduces computation time and requires less storage compared with full‐wave simulations. The results show that the hexagonal‐square metasurface absorber achieves exceptional absorption rates, with an average of 99.9% in the 431 to 532 nm wavelength range and over 90% in the 300 to 915 nm range. The hexagonal‐hexagonal metasurface absorber also exhibits high absorption rates, with an average of over 99% in the 431 to 518 nm and 700 to 780 nm ranges, and over 90% in the 300 to 940 nm range. The absorption performance of the proposed hexagonal‐circle metasurface absorber is also remarkable, with an absorption value of over 99% in the 670 to 771 nm range and above 90% in the 365 to 991 nm range. These models can be utilized to design and simulate other subwavelength absorbers in a broad frequency range, including terahertz and visible light, making them suitable for various applications.

Enhancement of terahertz emission from aqueous NaCl solutions

Exploration of terahertz sources with high electric fields and broad bandwidth is of great importance for terahertz application. In this work, the enhancement of terahertz emission from aqueous NaCl solutions induced by femtosecond laser pulses has been demonstrated by experiments. The power of the terahertz wave emission from the NaCl solution with a concentration of 30% is 1.86 times stronger than that from liquid water under equivalent excitation conditions. By means of a liquid circulation system with accurate pressure and temperature control, the influence of parameters such as solution concentration, liquid temperature, and medium size on the terahertz emission has been investigated. According to the experiment results, strong terahertz pulses are radiated from NaCl solutions with higher concentration, higher temperature, and smaller diameter. In addition, the physical mechanisms responsible for strong terahertz radiation have been analyzed by actual measurements and numerical simulations.

Total cross-polarization conversion and polarization-sensitive amplification of terahertz radiation in graphene with direct electric current

Total cross-polarization conversion and polarization-sensitive amplification of terahertz radiation in graphene with direct electric current

Single-cycle, 643 mW average power terahertz source based on tilted pulse front in lithium niobate.

We present the highest, to the best of our knowledge, average power from a laser-driven single-cycle THz source demonstrated so far, using optical rectification in the tilted pulse front geometry in cryogenically cooled lithium niobate, pumped by a commercially available 500 W ultrafast thin-disk ytterbium (Yb) amplifier. We study repetition rate-dependent effects in our setup at 100 and 40 kHz at this high average power, revealing different optimal fluence conditions for efficient conversion. The demonstrated sources with multi-100 mW average power at these high repetition rates combine high THz pulse energies and high repetition rate and are thus ideally suited for nonlinear THz spectroscopy experiments with significantly reduced measurement times. The presented result is a first benchmark for high average power THz time-domain spectroscopy systems for nonlinear spectroscopy, driven by very high average power ultrafast Yb lasers.

Theoretical Models for Performance Analysis of Spintronic THz Emitters

The terahertz (THz) region of the electromagnetic spectrum, spanning from 0.1 to 10 THz, offers unique opportunities for imaging, spectroscopy, and communication applications. However, the potential of THz technologies has been limited by the availability of efficient and versatile THz emitters. Spintronic THz emitters (STEs), leveraging the ultrafast dynamics of electron spins in magnetic materials, have emerged as a promising solution to this challenge. STEs offer significant advantages, including broad bandwidth, high power output, and room-temperature operation, positioning them at the forefront of THz technology development. Despite these advances, understanding the operational principles and improving the performance of STEs remain areas of active research. This review focuses on the theoretical models that describe the behavior of STEs, aiming to provide a comprehensive overview of the underlying physics and suggest directions for future enhancements. Through a detailed examination of these models, the review seeks to clarify the basics of the physics driving STE performance and highlight innovative strategies for their optimization and application expansion.

Stretchable terahertz metasurface based on laser induced graphene for contactless deformation sensing

In this paper, a 1D stretchable terahertz (THz) metasurface based on laser-induced graphene (LIG) for deformation sensing is developed with low cost, good sensitivity and robustness. After the LIG metasurface is fabricated by laser-direct writing on a polyimide film, it is divided into columns and bonded to a medical polyurethane (PU) tape, thus endowed with high elasticity due to the excellent flexibility of PU. Because LIG supports surface plasmon polaritons in the THz band, a plasmonic resonance is introduced in the reflection spectrum and red shifts with lateral stretching. Experimental results show that the device can realize a resonant frequency shift of 336 GHz at a deformation of 0-14 mm, and the linearity reaches 0.988, achieving a sensitivity of 24 GHz/mm and excellent robustness (>1000 repetitions). The LIG-based stretchable THz sensor has great application potential for contactless deformation sensing in aerospace, industrial manufacturing, and related fields.

Enhanced terahertz radiation generated by intense laser interaction with a two-layer thin solid target

A terahertz radiation enhancing scheme, in which a linearly polarized weakly relativistic laser pulse irradiates a target consisting of two parallel thin-solid layers with a certain gap, is proposed and studied by using two-dimensional particle-in-cell simulations. The radiation is known to be produced by laser-produced hot electrons via mechanisms such as coherent transition radiation at the target surfaces. Under optimized conditions, the energy conversion efficiency of terahertz radiation can be as high as 3.3%, which is nearly 1.5 times higher than that obtained with a single-layer target with the same drive laser. This is mainly due to the enhanced hot electron generation with moderate energy via multiple reflections of the laser pulse between the two target layers. The radiation has two peaks close to 30° from the target surface, which are more collimated than that with the single-layer target. The dependence of the terahertz radiation on a variety of target parameters is given, which can control the terahertz spectrum and radiation efficiency and thus provide guidance for experimental investigations. Moreover, both the coherent transition radiation and antenna radiation models are applied to explain the angular distributions of the terahertz emission found in the simulations. Published by the American Physical Society 2024

Propagation characteristics of obliquely incident terahertz waves in inhomogeneous microplasma

The transmission characteristics of terahertz (THz) waves in a non-uniform microplasma are investigated by using the scattering matrix method. The electron density distribution in microplasma is simulated by Epstein and parabolic models. The effects of physical parameters, such as the incidence angle of THz waves, microplasma size, electron density, and collision frequency, on the propagation of THz waves are numerically analyzed. The results show that lower frequency THz waves are difficult to penetrate the microplasma with high electron density and high collision frequency. The microplasma density distribution, especially the gradient variation of the density in the first layer, has a large effect on the reflection of THz waves. Thus, THz waves can be used to diagnose the physical parameters of microplasmas.

The dielectric response of a novel low-loss oxyfluoride Li0.5NaY9(SiO4)6O2F0.5 ceramic from Gigahertz band to Terahertz band

The exploration of dielectric ceramics with excellent dielectric responses at Gigahertz band and Terahertz band is becoming urgent for the upcoming 6th generation wireless communication. In this work, we propose a new approach to design novel dielectric ceramics by using the density functional theory. According to the analysis of Electron Localization Functions (ELF), Density of States (DOS) and crystal bond lengths, it indicates that the strategy of co-doping with lithium and fluorine will contribute to a much more stable crystal structure of Li0.5NaY9(SiO4)6O2F0.5 as compared to that of NaY9(SiO4)6O2. Furthermore, we report the innovative synthesis of a Li0.5NaY9(SiO4)6O2F0.5 oxyfluoride ceramic, a solid solution with a wide sintering temperature range, along with an in-depth analysis of its crystal structure, dielectric responses at both Gigahertz band and Terahertz band, which shows the promising application of Li0.5NaY9(SiO4)6O2F0.5 in the 6G wireless communication.