Generation Of Terahertz Radiation Research Articles

Controlled terahertz emission and electron localization dynamics in semiconductors

Dynamic localization has been thoroughly studied since 1986 by Dunlap in superlattice structures. However, its implications for terahertz (THz) radiation have not been fully explored. Here, we investigate the interplay between dynamic localization and THz radiation generation in semiconductor structures. Utilizing a two-color laser field, we reveal that intraband current is the primary source of THz radiation. Furthermore, we identify minima in THz radiation yield at specific laser field strengths, indicating the presence of dynamic localization. The relative phase of the two-color laser field and dephasing time can manipulate the extent and range of dynamic localization, thereby influencing the efficiency of THz radiation. Our findings provide valuable insights into simultaneous investigations on materials across different time scales.

THz generation and spatiotemporal variation of two cross‐focused Gaussian laser pulses in plasma

AbstractThe impact of spatial and temporal evolution of nonlinear mixing of two Gaussian laser pulses propagating in plasma on generation of terahertz (THz) radiation have been investigated taking into account the ponderomotive nonlinearity. By calculating the modified electron density of plasma caused by the finite ponderomotive force of the pump lasers and using wave equation and paraxial ray approximation, two coupled governing equations for temporal and spatial pulse‐width parameters have been derived. The electric field of the THz wave as a result of nonlinear current density induced by the beat ponderomotive force of the pulses was extracted. Combined effects of initial laser and plasma parameters on the behavior of self‐compression and self‐focusing as well as THz radiation generation were investigated. The numerical results indicated a considerable spatiotemporal compression takes place within a specific range of laser intensity, exhibiting a saturation intensity point where the compression process reaches its maximum extent. It is observed that the generated THz radiation also strongly depends on the spatiotemporal dynamics of the pump pulses. The maximum THz amplitude corresponds to the strongest pump pulse compression extent.

THz radiation generation from plasma wakefield driven by skew-cosh-Gaussian laser beam under an undulator magnetic field

The paper examines theoretically the generation of terahertz (THz) radiation as a result of wakefields generated by skew-cosh-Gaussian (skew-chG) laser beam propagating in collisional plasma under an undulator magnetic field. Analytical and non-linear equations have been derived to describe the generation of THz radiation by skew-chG laser beam. Using equations of motion, continuity equations, and perturbation technique, the transverse and longitudinal wakefield has also been derived in the presence of an undulator magnetic field. It is shown that the collisional plasma carries a higher longitudinal wakefield amplitude while the undulator amplitudes are lower. In addition, it is found that smaller collision frequencies make larger wakefield amplitudes that generate terahertz radiation. However, when the collision frequency becomes equal to the plasma frequency, the wakefield amplitude is greatly reduced. Moreover, it is observed that the THz field decreases with the increase of the beam waist of the skew-chG laser beam. It is also shown that the THz field exhibits an increasing behavior with increasing s parameter and undulator amplitudes despite the presence of significant collisions.

Generation of THz radiation through molecular modulation in hydrogen-filled hybrid anti-resonant fibers.

We study the generation of narrowband terahertz (THz) pulses by stimulated Raman scattering and molecular modulation in hydrogen-filled hybrid hollow-core fibers. Using a judicious combination of materials and transverse structures, this waveguide design enables simultaneous confinement of optical and THz signals with reasonably low attenuation, as well as high nonlinear overlap. The THz pulses are then generated as the second Stokes band of a ns-long near-infrared pump pulse, aided by Raman coherence waves excited in the gaseous core by the beat-note created by the pump and its first Stokes band. Optimization of the fiber characteristics facilitates phase matching between the corresponding transitions and coherence waves while avoiding coherent gain suppression, resulting in potential optical-to-THz conversion efficiencies up to 60%, as confirmed by rigorous numerical modelling under ideal zero-loss conditions. When the current optical material constraints are considered, however, the attainable efficiencies relax to 0.2%, a still competitive value compared to other systems. The approach is in principle power and energy scalable, as well as tunable in the 1-10 THz range without any spectral gaps, thereby opening new pathways to the development of fiber-based THz sources complementary to other mature technologies such as quantum cascade lasers.

Terahertz and far infrared radiation generation in air plasma created by bichromatic subpicosecond laser pulses

Here, we report on terahertz (THz) radiation generation in air driven by the fundamental and second harmonic of Yb:KGW laser pulses with durations of a few hundred femtoseconds. It was found that the spectrum of generated THz pulses surprisingly spans up to 50 THz, which is comparable to that usually obtained using much shorter Ti:sapphire laser pulses. The broad bandwidth is attributed to a strong spatiotemporal reshaping of the pump pulses in a filament. The achieved energy conversion efficiency is comparable to the one usually obtained from much shorter pump pulses and could be further improved by an optimized experimental setup. The obtained results indicate that compact Yb-based sources provide an attractive alternative to much larger and expensive laser systems.

Investigation of terahertz radiation generation from laser-wakefield acceleration

We investigate the generation of terahertz (THz) radiation from laser-wakefield acceleration (LWFA) in a helium gas jet. We consider a three-dimensional setup incorporating a realistic gas density distribution and use particle-in-cell simulations to study the interaction of a femtosecond intense laser pulse with the gas medium. Our results show that LWFA can efficiently produce THz radiation. In the simulations, we use multiple probes to record the electric and magnetic fields arising from the interaction. In addition, we compare the results of fixed and moving window simulation boxes used to capture electromagnetic fields in the THz range. We demonstrate that a moving window with a 600 μm width can be significantly useful for THz studies. We further analyze the spectrum of spatially and temporally resolved electromagnetic radiation and its emission angle. Our results are consistent with experimental data. Our findings provide valuable insights into the potential of LWFA as a strong source of THz radiation.

Generation of Terahertz Radiation by Relativistic Laser Pulses on the Surface of Thick Solid Targets and Thin Foils

Terahertz pulse generation from multiterawatt laser surface plasma near thick solid targets and thin foils has been studied. Pulses with energies up to 7 μJ were detected in the spectral region <3 THz in the direction of specular reflection from the surface of the CaF2 target. The dependence of the terahertz pulse energy \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{W}_{{{\ ext{THz}}}}}$$\\end{document} on the laser pulse intensity \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$I_{L}^{\\alpha }$$\\end{document} can be approximated by the power function \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{W}_{{{\ ext{THz}}}}} \\sim I_{L}^{\\alpha }$$\\end{document}. For a fixed laser pulse duration and variable energy the power index lies in the range \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha \\approx 1.5{-} 2.8$$\\end{document}, while for a fixed energy and variable duration \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha \\approx 1$$\\end{document}.

Terahertz radiation generation from amplitude-modulated laser filament interaction with a magnetized plasma

The availability of high-power lasers open new frontiers of Terahertz (THz) optics. In this paper, we present a mechanism for the enhanced THz field generation from the laser wakefield excitation during the interaction of an amplitude-modulated laser filament with a magnetized plasma. The derivation of electric and magnetic wakefields in axially magnetized plasma is obtained using the perturbative approach. Amplitude-modulated laser filament generates a significantly stronger transverse current due to laser intensity redistribution by the amplitude modulation. The modulation index of the amplitude modulated laser pulse is used to control the transverse current at THz frequency. Fourfold enhancement takes place in THz field strength for higher values of the modulation index (0–0.4). Also, the conversion efficiency of this mechanism is estimated as [Formula: see text] that can be enhanced for higher modulation index. Scaling laws are provided for controlling and optimization of generated THz field. This work may be crucial in exploring THz optical phenomena such as THz field-induced Kerr effects and many other nonlinear effects.

Recent progress of THz source at the SXFEL

Coherent, wide-tunable frequency and high intensity terahertz (THz) source is under preparation at the Shanghai Soft X-ray free-electron laser facility (SXFEL). The electron bunches modulated by frequency beating light can generate coherent, wide-tunable, high intensity THz radiation from 0.1 to 30 THz through wigglers. The electromagnetic wiggler with peak magnetic field up to 1.75 T is adopted and the parameters of the wiggler are optimized to ensure the generation of strong field THz radiation. Due to the limitation of layout space of the SXFEL, the length of wiggler is limited within 5 meters. By properly increasing the charge of the electron beam, the THz pulse energy can be kept at sub mJ level under the proposed different parameters of the wiggler. In this article, we will present the possible layout of THz source on the SXFEL and the S2E simulation of THz radiation of sub mJ magnitude within the 5-meter wiggler.

Optimal Dirichlet boundary control by Fourier neural operators applied to nonlinear optics

We present an approach for solving optimal boundary control problems of nonlinear optics by using deep learning. For computing high resolution approximations of the solution to the nonlinear wave model, we propose higher order space-time finite element methods in combination with collocation techniques. Thereby, Cl-regularity in time of the global discrete solution is ensured. The simulation data is used to train solution operators that effectively leverage the higher regularity of the data. The solution operator is represented by Fourier Neural Operators and can be used as the forward solver in the optimal Dirichlet boundary control problem.The proposed algorithm is implemented and tested on high-performance computing platforms, with a focus on efficiency and scalability. The effectiveness of the approach is demonstrated on the problem of generating Terahertz radiation in periodically poled Lithium Niobate. The neural network is used as the solver in the optimal control setting to optimize the parametrization of the optical input pulse and maximize the yield of 0.3THz-frequency radiation.We exploit the periodic layering of the crystal to design the neural networks. The networks are trained to learn the propagation through one period of the layers. The recursive application of the network onto itself yields an approximation to the full problem. Our results indicate that the proposed method can achieve a speedup by a factor of 360 compared to classical methods. A comparison of our results to experimental data shows the potential to revolutionize the way we approach optimization problems in nonlinear optics.

High-Frequency Shift and Extension of the Terahertz Radiation Spectrum up to 10 THz During Optical Rectification of High-Power Few-Cycle Near-Infrared Femtosecond Pump Radiation in a BNA Crystal

The generation of terahertz radiation in a BNA crystal pumped by 1.24-µm femtosecond laser radiation from a Cr:forsterite laser system with a pulse duration of 100 and 35 fs and a pump density of 10 mJ/cm2 has been realized. The achieved generation efficiency is 0.1%. It is found that a decrease in the pump pulse duration from 100 to 35 fs leads to the generation of high-frequency components in the ranges of 2.5–6.5 THz and 9‒10.5 THz in the generated radiation spectrum. Simulation of the terahertz radiation generation based on the solution of Maxwell’s equations by the finite-difference time-domain method has made it possible to adequately describe the measured spectra. The generation of broadband high-frequency terahertz radiation in the BNA crystal pumped by the Cr:forsterite laser system allows one to consider this schematic as an alternative to sources based on the BNA crystal pumped by a Ti:sapphire laser system.

Variable laser profiles and polarization states in the wave-mixing scheme for the generation of THz radiation in collisional-magnetized clustered-plasma

The four-wave mixing (FWM) mechanism for the generation of Terahertz (THz) radiation in magnetized-collisional clustered-plasma is studied. Clusters can trap the incident laser fields, leading to efficient energy transfer to plasma electrons and the creation of a strong nonlinear current. The size and density of clusters can be tuned to control the emission of THz radiation. The smaller clusters can bring about higher intensity THz radiation, while larger clusters can contribute to the broader THz frequency range. The THz radiation angular distribution patterns in the forward direction have been assessed, and the impact of plasma interaction length, cluster radius, and plasma electrons collision frequency on the generated THz wave patterns has been investigated. The FWM analysis highlights the importance of plasma clusters as well as magnetic fields in the efficient generation of THz emission. The model also takes into consideration how an induced electron current density initiated by DC external magnetic field can boost radiation power without changing the directivity diagram.

External Periodic Field and Skew-chG Beams for Generation of Multifocal Terahertz Radiation in Collisional Plasma

External Periodic Field and Skew-chG Beams for Generation of Multifocal Terahertz Radiation in Collisional Plasma

Propagation of THz radiation in air over a broad range of atmospheric temperature and humidity conditions

As the need for higher data rates for communication increases, the terahertz (THz) band has drawn considerable attention. This spectral region promises a much wider bandwidth and the transmission of large amounts of data at high speeds. However, there are still challenges that need to be addressed before the THz telecommunications technology hits the consumer market. One of the recurring concerns is that THz radiation is greatly absorbed by atmospheric water-vapor. Although many studies have presented the attenuation of THz signals under different atmospheric conditions, these results analyze specific temperature or humidity values, leaving the need for a more comprehensive analysis over a wider range of climate conditions. In this work, we present the first study of the attenuation of THz radiation over a broad range of temperatures and humidity values. It is worth noticing that all of our measurements have been undertaken at atmospheric pressure unlike many previous studies where the pressure was not kept constant for various temperatures. Furthermore, we extend our analysis beyond the impact of absolute humidity on the bit error rate in THz communications. We also discuss the refractivity of the atmosphere, examining its variations across different temperatures and humidity levels. THz propagation is studied using two different measurement systems, a long-path THz time-domain spectrometer as well as a quasi-optic setup with vector network analyze. We also compare the results with the ITU-R P.676-13 propagation model. We conclude that the attenuation at the absorption peaks increases linearly with water content and has no dependence on the temperature, while the refractive index, away from absorption lines, namely at 300 GHz shows a sub-linear increase with humidity.

Numerical study of ultrafast optical instability causing structured light absorption in metal

We present the first-principle numerical study of nonlinear decay of a femtosecond laser pulse into a pair of surface plasmon polaritons (SPP) during reflection from a rough metallic surface. The ultrafast dynamics of the decay was studied at damaging laser fluences of about 1 J/cm2, and the principal role of the electronic collision rate growth was proved. The resulting strongly inhomogeneous heating of metal is an important stage of laser-induced phenomena like ablation, terahertz radiation generation, and periodic surface structures formation.

A semi-analytical and semi-numerical method for solving plasma instability of nonuniform two-dimensional electron gas

The plasma instability of two-dimensional electron gas (2DEG) is a crucial physical mechanism for generating terahertz radiation in field-effect transistors, especially in high electron mobility transistors (HEMTs). In this paper, we have proposed a new semi-analytical and semi-numerical method to deal with oscillation problems of any nonuniform 2DEG plasma, especially considering the steady-state distribution, which can be calculated and analyzed more quickly than only using numerical calculation. By constructing a wave equation, using the auxiliary function and Wentzel–Kramers–Brillouin approximation method, the wave vector of the plasma wave is obtained. On this basis, combined with the Dyakonov–Shur instability's boundary conditions, the oscillation frequency, the wave amplitude increment, and their correction caused by the nonuniformity can be obtained by numerical calculation. Furthermore, the analytical solution is obtained under reasonable approximate conditions for the linear distribution of electron concentration. It is proved that the electron concentration gradient in the channel will not only attenuate the wave increment but also decrease the plasmonic frequency in the case of linear distribution. Moreover, we get the reasons for the above conclusions through theoretical derivation. We also investigate the effects of various device parameters on attenuation, such as gate length, electron mobility, and voltage, which may explain the difference between the actual and theoretical values in HEMTs and provide new guidance for device design.

Generation of Terahertz Radiation in Boron-Doped Diamond

Generation of Terahertz Radiation in Boron-Doped Diamond

Enhancement of Terahertz radiation due to excitation of SPW on graphene strip coated on GaAs structure

The present study proposes a methodology for improving terahertz (THz) radiation through the utilisation of a laser directed towards a graphene strip that has been coated onto a GaAs structure. The presence of a non-uniform voltage results in the production of a transient current when the laser interacts with GaAs material. The generation of THz radiation is attributed to the current that is produced along the length of GaAs structures. Concurrently, a portion of the laser beam interacts with the graphene strip, inducing a surface plasma wave (SPW) that propagates along the surface of the graphene. The amplitude of the SPW experiences an exponential decay as it travels away from the interface in both the media. The impact of the transverse electric field of surface plasmon waves in graphene on the transient current in GaAs material has been observed to enhance THz radiation. The frequency of the SPW increases in a parabolic manner as the graphene strip increases with rises with rise in propagation vector. The plasmonics (Graphene plasmons: GPs) approach used for the proposed model enables us to making the emitted radiation suitable for Terahertz spectroscopy, imaging and non-destructive testing, Highspeed data transfer, Terahertz microscopy, Terahertz microscopy, Terahertz microscopy, Quantum technology.

Terahertz emission with remarkable efficiency through spherical nanoparticles using dark-hollow-Gaussian beams

Simultaneous tuning of Terahertz (THz) radiation with respect to its frequency, power and focus is still a challenge for the scientific community, because of which its use is lacking in several areas. To achieve such properties, the present work proposes monodisperse graphite nanoparticles (NPs) of spherical shape dispersed in two orthogonal directions with normal vector of their basal planes parallel and perpendicular to the electric field of the dark-hollow-Gaussian beams (DHGBs) used for the generation of THz radiation. The NPs are impinged upon by two DHGBs of slightly different frequencies, which exert a ponderomotive force on the conduction electrons of the NPs. The motion of these electrons under the action of high intensity laser beams constitutes a macroscopic nonlinear current that produces the THz radiation. The well-structured THz emission occurs with the efficiency reaching 10−2 when the NPs resonate with the beating frequency, and they are arranged in their parallel orientations with respect to the electric field of the lasers. The proposal and the obtained results will contribute to the THz science and technology along with their use in medical science and THz time-domain spectroscopy.

Generation of Terahertz Radiation via the Transverse Thermoelectric Effect.

Terahertz (THz) radiation is a powerful tool with widespread applications ranging from imaging, sensing, and broadband communications to spectroscopy and nonlinear control of materials. Future progress in THz technology depends on the development of efficient, structurally simple THz emitters that can be implemented in advanced miniaturized devices. Here, it is shown how the natural electronic anisotropy of layered conducting transition metal oxides enables the generation of intense terahertz radiation via the transverse thermoelectric effect. In thin films grown on off-cut substrates, femtosecond laser pulses generate ultrafast out-of-plane temperature gradients, which in turn launch in-plane thermoelectric currents, thus allowing efficient emission of the resulting THz field out of the film structure. This scheme is demonstrated in experiments on thin films of the layered metals PdCoO2 and La1.84 Sr0.16 CuO4 , and model calculations that elucidate the influence of the material parameters on the intensity and spectral characteristics of the emitted THz field are presented. Due to its simplicity, the method opens up a promising avenue for the development of highly versatile THz sources and integrable emitter elements.