Ultrasensitive Terahertz Label-Free Metasensors Enabled by Quasi-Bound States in the Continuum.

Advanced sensing devices based on metasurfaces have emerged as a revolutionary platform for innovative label-free biosensors, holding promise for early diagnostics and the detection of low-concentration analytes. Here, we developed a chip-based ultrasensitive terahertz (THz) metasensor, leveraging a quasi-bound state in the continuum (BIC) to address the challenges associated with intricate operations in trace biochemical detection. The metasensor design features an open-ring resonator metasurface, which supports magnetic dipole -BIC combining functionalized gold nanoparticles (AuNPs) bound with a specific antibody.

GeTe Phase Change Material for Terahertz Devices with Reconfigurable Functionalities Using Optical Activation.

The phenomenon of phase change transition has been a fascinating research subject over decades due to a possibility of dynamically controlled materials properties, allowing the creation of optical devices with unique features. The present paper unravels the optical characteristics and terahertz (THz) dielectric permittivity of a novel phase change material (PCM), GeTe, prepared by pulsed laser deposition (PLD) and their remarkable contrast in crystalline and amorphous states, in particular, a difference of 7 orders of magnitude in conductivity. The THz spectra were analyzed using the harmonic oscillator and Drude term.

Discovering Glioma Tissue through Its Biomarkers' Detection in Blood by Raman Spectroscopy and Machine Learning.

The most commonly occurring malignant brain tumors are gliomas, and among them is glioblastoma multiforme. The main idea of the paper is to estimate dependency between glioma tissue and blood serum biomarkers using Raman spectroscopy. We used the most common model of human glioma when continuous cell lines, such as U87, derived from primary human tumor cells, are transplanted intracranially into the mouse brain.

Graphene plasmons-enhanced terahertz response assisted by metallic gratings.

Terahertz detectors based on two-dimensional Dirac materials offer a new approach for room-temperature terahertz detection with high response and low noise. However, these devices can hardly show high response over a broad frequency range, mainly due to the poor absorption caused by their ultrathin nature. Here we apply metallic gratings to enhance the excitation efficiency of graphene plasmons.

Label-free laser spectroscopy for respiratory virus detection: A review.

Infectious diseases are among the most severe threats to modern society. Current methods of virus infection detection based on genome tests need reagents and specialized laboratories. The desired characteristics of new virus detection methods are noninvasiveness, simplicity of implementation, real-time, low cost and label-free detection.

Photoinduced large polaron transport and dynamics in organic-inorganic hybrid lead halide perovskite with terahertz probes.

Organic-inorganic hybrid metal halide perovskites (MHPs) have attracted tremendous attention for optoelectronic applications. The long photocarrier lifetime and moderate carrier mobility have been proposed as results of the large polaron formation in MHPs. However, it is challenging to measure the effective mass and carrier scattering parameters of the photogenerated large polarons in the ultrafast carrier recombination dynamics.

Measuring heavy metal ions in water using nature existed microalgae as medium based on terahertz technology.

Heavy metal pollution in water seriously affects human health. The disadvantages of traditional metal ion detection methods involve long and cumbersome chemical pretreatment in the early stage, and large volume of samples. In this study, microalgae were used as the medium, and terahertz spectroscopy technology was employed to collect the changes of material components in it, so as to deduce the types and concentrations of heavy metal pollution in water.

A monoclinic semiorganic molecular crystal GUHP for terahertz photonics and optoelectronics.

In this paper we describe the properties of the crystal of guanylurea hydrogen phosphate (NH[Formula: see text])[Formula: see text]CNHCO(NH[Formula: see text])H[Formula: see text]PO[Formula: see text] (GUHP) and propose its application in terahertz photonics and optoelectronics. GUHP crystal has a wide window of transparency and a high optical threshold in the visible and NIR spectral regions and narrow absorption bands in the terahertz frequency range. The spectral characteristics of absorption and refraction in the THz range were found to be strongly dependent on crystal temperature and orientation.

Tunable Transmissive Terahertz Linear Polarizer for Arbitrary Linear Incidence Based on Low-Dimensional Metamaterials.

In this work, we propose a structure consisting of three metamaterial layers and a metallic grating layer to rotate the polarization of arbitrary linearly polarized incidence to the y-direction with high transmissivity by electrically tuning these metamaterials. The transfer matrix method together with a harmonic oscillator model is adopted to theoretically study the proposed structure. Numerical simulation based on the finite difference time-domain method is performed assuming that the metamaterial layers are constituted by graphene ribbon arrays.

Transient optical non-linearity in p-Si induced by a few cycle extreme THz field.

We study the impact of a few cycle extreme terahertz (THz) radiation (the field strength E ∼1-15 MV/cm is well above the DC-field breakdown threshold) on a p-doped Si wafer. Pump-probe measurements of the second harmonic of a weak infrared probe were done at different THz field strengths. The second harmonic yield has an unusual temporal behavior and does not follow the common instantaneous response, ∝TH2.

Malignant and benign thyroid nodule differentiation through the analysis of blood plasma with terahertz spectroscopy.

The liquid and lyophilized blood plasma of patients with benign or malignant thyroid nodules and healthy individuals were studied by terahertz (THz) time-domain spectroscopy and machine learning. The blood plasma samples from malignant nodule patients were shown to have higher absorption. The glucose concentration and miRNA-146b level were correlated with the sample's absorption at 1 THz.

Terahertz spectroscopy of diabetic and non-diabetic human blood plasma pellets.

Significance: The creation of fundamentally new approaches to storing various biomaterial and estimation parameters, without irreversible loss of any biomaterial, is a pressing challenge in clinical practice. We present a technology for studying samples of diabetic and non-diabetic human blood plasma in the terahertz (THz) frequency range.

Aim: The main idea of our study is to propose a method for diagnosis and storing the samples of diabetic and non-diabetic human blood plasma and to study these samples in the THz frequency range.

Terahertz Broadband Polarization Conversion for Transmitted Waves Based on Graphene Plasmon Resonances.

We applied the harmonic oscillator model combined with the transfer matrix method to study the polarization conversion for transmitted waves in metallic grating/plasmon-excitation layer/metallic grating structure in the terahertz (THz) region. By comparing the calculated spectra and the simulated (by the finite-difference-time-domain method) ones, we found that they correspond well with each other. Both methods show that the Drude background absorption and the excited plasmon resonances are responsible for polarization conversion.

Geometry phase for generating multiple focal points with different polarization states.

Conventional lenses are always large and bulky to achieve desired wave-manipulating functions, hindering the development of integrated and miniaturized optical systems. Metasurfaces, two-dimensional counterparts of metamaterials, can accurately tailor the wavefront of electromagnetic waves at subwavelength scale, providing a flexible platform for designing ultra-compact and ultra-flat lenses, namely as metalenses. However, the previous geometry-phase-based metalenses usually generate focal point(s) with only one special polarization state, i.

Excitation of graphene surface plasmons polaritons by guided-mode resonances with high efficiency.

An Otto-like configuration for the excitation of graphene surface plasmon polaritons (GSPPs) is proposed. The configuration is composed of a metallic grating-dielectric-waveguide structure and a monolayer graphene with a subwavelength vacuum gap between them. The evanescent field located at the bottom surface of the dielectric waveguide corresponding to grating-coupled guided-mode resonances (GMRs) is utilized to efficiently excite the highly confined GSPPs.

Multiband and broadband active controllable terahertz absorption in dual-side grating-gate graphene field-effect transistors.

We show that the even order ungated modes can be excited under normal incidence while the odd order ungated modes cannot in traditional single-side grating-gate graphene field-effect transistors. The odd order ungated modes will suppress the excitation efficiency of the gated modes. In order to realize multiband detection by effectively exciting the higher order gated modes, the frequency of the 1st order ungated mode should be tuned up, which can be realized by shortening the length of the ungated region.

Terahertz-frequency temporal differentiator enabled by a high-Q resonator.

Terahertz (THz) fundamental "building blocks" equivalent to those used in multi-functional electronic circuits are very helpful for actual applications in THz data-processing technology and communication. Here, we theoretically and experimentally demonstrate a THz temporal differentiator based on an on-chip high-quality (Q) factor resonator. The resonator is made of low-loss high-resistivity silicon material in a monolithic, integrated platform, which is carefully designed to operate near the critical coupling region.

Metal-graphene hybridized plasmon induced transparency in the terahertz frequencies.

In this work, metal-graphene hybridized plasmon induced transparency (PIT) is systematically studied in the proposed simple metal/dielectric/graphene system. The PIT effect is the result of the coupling between the bright dipolar modes excited in the graphene regions under the shorter metallic bars and the dark quadrupolar modes excited in the graphene regions under the longer metallic bars. The coupled Lorentz oscillator model is used to help explain the physical origin of the PIT effect.

"Terhune-like" transformation of the terahertz polarization ellipse "mutually induced" by three-wave joint propagation in liquid.

In this Letter, we show experimentally for the first time, to the best of our knowledge, the possibility to observe the effect of polarization mutual action of three elliptically polarized waves, with one of them at terahertz frequency, when they propagate in the isotropic nonlinear medium. When three light pulses are propagated at frequencies , 2, and through liquid nitrogen, we observed the rotation of the ellipse main axis and the ellipticity change. We have shown that this effect is very well described theoretically in the framework of a physical approach analogous to the self-rotation of the polarization ellipse first described in 1964 by Maker et al.

Nitroxoline Molecule: Planar or Not? A Story of Battle between π-π Conjugation and Interatomic Repulsion.

The conformational properties of the nitro group in nitroxoline (8-hydroxy-5-nitroquinoline, NXN) were investigated in the gas phase by means of gas electron diffraction (GED) and quantum chemical calculations, and also with solid-state analysis performed using terahertz time-domain spectroscopy (THz-TDS). The results of the GED refinement show that in the equilibrium structure the NO group is twisted by angle ϕ = 8 ± 3° with respect to the 8-hydroxyoquinoline plane. This is the result of interatomic repulsion of oxygen in the NO group from the closest hydrogen, which overcomes the energy gain from the π-π conjugation of the nitro group and aromatic system of 8-hydroxyoquinoline.

Impact of the dipole contribution on the terahertz emission of air-based plasma induced by tightly focused femtosecond laser pulses.

The present paper studies the generation mechanism of terahertz (THz) radiation from tightly focused femtosecond laser pulses in a gas medium. We measured the angular radiation pattern under different focusing conditions and observed that, with the deepening of focus, the angular radiation pattern changes and optical-to-THz conversion efficiency increases. The analysis of the observed phenomena led to the assumption that the dipole radiation prevails in most cases despite the existing conception regarding the dominating role of the quadrupole mechanism of radiation.

Possibility of direct estimation of terahertz pulse electric field.

In this Letter, we introduce a new method of estimation of the terahertz (THz) field amplitude. This method uses second-harmonic generation (SHG) in the presence of THz and DC fields in gaseous media. We take into account contributions from both nonionized molecules and free plasma electrons to the nonlinear process of SHG.

Design rules for phase-matched terahertz surface electromagnetic wave generation by optical rectification in a nonlinear planar waveguide.

The theory of guided waves in metal-dielectric planar multilayer structures is applied to reduce the loss and maximize optical nonlinearity for efficient terahertz-field generation in a surface electromagnetic wave by femtosecond laser pulses confined in a (chi)((2)) nonlinear planar waveguide. For typical parameters of thin-film polymer waveguides and metal-dielectric interfaces, the optimal size of the (chi)((2)) waveguide core providing the maximum efficiency of terahertz plasmon-field generation is shown to be less than the wavelength of the optical pump field.