A repository & source of cutting edge news about emerging terahertz technology, it's commercialization & innovations in THz devices, quality & process control, medical diagnostics, security, astronomy, communications, applications in graphene, metamaterials, CMOS, compressive sensing, 3d printing, and the Internet of Nanothings. NOTHING POSTED IS INVESTMENT ADVICE! REPOSTED COPYRIGHT IS FOR EDUCATIONAL USE.
Terahertz (THz) technology is increasingly being
used in a wide range of applications, and terahertz radar systems have also
been developed in radar applications. In this paper, the terahertz radar system
is used for 2 dimensional (2D) realtime imaging in near-field scenario within
20m. A real-time imaging system of 170GHz Synthetic Aperture Radar (SAR) is
designed, and the system is simulated and verified by Doppler Beam Sharpening
(DBS) algorithm. The simulation results show that the system can utilize
uniform linear motion to synthesize a short aperture in the near-field range
and form 2D image of scattering points in the scene. The imaging effect is good.
Yuanyuan Li, Ning Yang, Yan Xie, Weidong Chu, Wei Zhang, Suqing Duan, and Jian Wang
Fig. 2 Time evolution of |EA|, |EB | (first column), the corresponding power spectral density (second column), and instantaneous frequency (third column) with different coupling strength κ and detuning frequency ΔΩ/2π. The coupling strength in the first three rows are set as κ = 9.87 × 10−3, which is the case of moderate coupling. (a)–(c) within the phase-locking regime, ΔΩ/2π = 0.5GHz, (d)–(f) out of the pahse-locking regime, ΔΩ/2π = 5GHz, (g)–(i) out of the pahse-locking regime, ΔΩ/2π = 0.55GHz. The fourth row is the case of strong coupling with κ = 0.247. (j)–(l) out of the pahse-locking regime, ΔΩ/2π = 0.2GHz. The effective injection current is 1.5Ith in all simulations.
The phase-locking, noise, and modulation properties of two face-to-face optically mutual-injected terahertz (THz) quantum cascade lasers (QCLs) are analyzed theoretically. In the phase-locking range, the two THz QCLs are in stationary states working at the same frequency. Outside the phase-locking range, the amplitude and the instantaneous frequency of the optical field oscillate with time, and the power spectrum shows a series of discrete peaks. For strong mutual injection, the optical field of the THz QCL array also exhibits oscillatory behavior. Coherent collapse or chaotic behavior is not observed within the range of the parameters used in this simulation. The spontaneous emission noise of phase-locked THz QCLs is higher than that of THz QCLs at free-running operation, and mutual injection may introduce additional modulation peaks in the noise spectrum. The modulation response of the mutual-injected THz QCLs to an individual modulation is investigated. It is found that the modulation bandwidth and the phase difference are significantly dependent on the modulation parameters. These results are helpful for further understanding the nonlinear dynamic behaviors of THz QCLs under optical injection and provide theoretical support for the development of THz QCL phase-locked arrays.
We observed a clear superconducting gap at 2.0meV and a coherent peak in the strong spin fluctuation compounds LiTi2O4 using continues wave (CW) terahertz spectroscopy. The superconducting state was strongly suppressed by magnetic fields.
We show that a femtosecond spin-current pulse can generate terahertz (THz) transients at Rashba interfaces between two nonmagnetic materials. Our results unambiguously demonstrate the importance of the interface in this conversion process that we interpret in terms of the inverse Rashba Edelstein effect, in contrast to the THz emission in the bulk conversion process via the inverse spin-Hall effect. Furthermore, we show that at Rashba interfaces the THz-field amplitude can be controlled by the helicity of the light. The optical generation of electric photocurrents by these interfacial effects in the femtosecond regime will open up new opportunities in ultrafast spintronics.
The low-frequency motions of molecules in the condensed phase have been shown to be vital to a large number of physical properties and processes. However, in the case of disordered systems, it is often difficult to elucidate the atomic-level details surrounding these phenomena. In this work, we have performed an extensive experimental and computational study on the molecular solid camphor, which exhibits a rich and complex structure-dynamics relationship, and undergoes an order-disorder transition near ambient conditions. The combination of x-ray diffraction, variable temperature and pressure terahertz time-domain spectroscopy, ab initio molecular dynamics, and periodic density functional theory calculations enables a complete picture of the phase transition to be obtained, inclusive of mechanistic, structural, and thermodynamic phenomena. Additionally, the low-frequency vibrations of a disordered solid are characterized for the first time with atomic-level precision, uncovering a clear link between such motions and the phase transformation. Overall, this combination of methods allows for significant details to be obtained for disordered solids and the associated transformations, providing a framework that can be directly applied for a wide range of similar systems.
In this paper we theoretically and experimentally demonstrate a stepped-refractive-index convergent lens made of a parallel stack of metallic plates for terahertz frequencies based on artificial dielectrics. The lens consist of a non-uniformly spaced stack of metallic plates, forming a mirror-symmetric array of parallel-plate waveguides (PPWGs). The operation of the device is based on the TE1 mode of the PPWG. The effective refractive index of the TE1 mode is a function of the frequency of operation and the spacing between the plates of the PPWG. By varying the spacing between the plates, we can modify the local refractive index of the structure in every individual PPWG that constitutes the lens producing a stepped refractive index profile across the multi stack structure. The theoretical and experimental results show that this structure is capable of focusing a 1 cm diameter beam to a line focus of less than 4 mm for the design frequency of 0.18 THz. This structure shows that this artificial-dielectric concept is an important technology for the fabrication of next generation terahertz devices.
Wei Zhang, Wei He, Xiang-Qun Zhang, Zhao-Hua Cheng, Jiao Teng, and Manfred Fähnle https://journals.aps.org/prb/accepted/c2075Y25Ia810e5b542200726ae86a14d2dd92127 The ability to controllably manipulate the laser-induced ultrafast magnetic dynamics is a prerequisite for future high speed spintronic devices. The optimization of devices requires the controllability of the ultrafast demagnetization time, \begin{figure}[htbp] } \label{fig1} \end{figure} , and intrinsic Gilbert damping, \begin{figure}[htbp] } \label{fig2} \end{figure} . In previous attempts to establish the relationship between \tauM and \alphaintr , the rare-earth doping of a permalloy film with two different demagnetization mechanism is not a suitable candidate. Here, we choose Co/Ni bilayers to investigate the relations between \begin{figure}[htbp] } \label{fig3} \end{figure} and \begin{figure}[htbp] } \label{fig4} \end{figure} by means of time-resolved magneto-optical Kerr effect (TRMOKE) via adjusting the thickness of the Ni layers, and obtain an approximately proportional relation between these two parameters. The remarkable agreement between TRMOKE experiment and the prediction of breathing Fermi-surface model confirms that a large Elliott-Yafet spin-mixing parameter b2 is relevant to the strong spin-orbital coupling at the Co/Ni interface. More importantly, a proportional relation between \tauM and \alpha \mbox{intr} in such metallic films or heterostructures with electronic relaxation near Fermi surface suggests the local spin-flip scattering domains the mechanism of ultrafast demagnetization, otherwise the spin-current mechanism domains. It is an effective method to distinguish the dominant contributions to ultrafast magnetic quenching in metallic heterostructures by investigating both the ultrafast demagnetization time and Gilbert damping simultaneously. Our work can open a novel avenue to manipulate the magnitude and efficiency of Terahertz emission in metallic heterostructures such as the perpendicular magnetic anisotropic Ta/Pt/Co/Ni/Pt/Ta multilayers, and then it has an immediate implication of the design of high frequency spintronic devices.https://journals.aps.org/prb/accepted/c2075Y25Ia810e5b542200726ae86a14d2dd92127
We report new models for out-of-plane focusing and manipulation of terahertz beams based on a silicon/copper grating covered by monolayer graphene. Dependences of focusing and manipulation of terahertz beams on the chemical potential and scattering rate of graphene are investigated. Based on the graphene/silicon grating model, we demonstrate that the focal distance and intensity are sensitively influenced by the chemical potential. Based on the graphene/copper grating model, we show how 2 to 1 and 3 to 1 modulation of terahertz beams can be efficiently realized through tuning the chemical potential of graphene. These tunable beam focusing and manipulation effects are well explained by the diffraction theory of optical images and the surface plasmon polariton theory of graphene. Our proposed devices are of compact structures, high electro-optical tunability and good repeatability, and they are expected to have prospective applications in terahertz communications, imaging, sensing, and so on.
Brown University researchers have developed a new kind of polarizing beamsplitter for terahertz radiation, which could prove useful in imaging and communications systems.
PROVIDENCE, R.I. [Brown University] — Brown University researchers have developed a new method of manipulating the polarization of light at terahertz frequencies.
The technique uses stacks of carefully spaced metal plates to make a polarizing beamsplitter, a device that splits a beam of light by its differing polarization states, sending vertically polarized light in one direction and horizontally polarized light in another. Such a beamsplitter could be useful in a wide variety of systems that make use of terahertz radiation, from imaging systems to future communications networks.
In the imaging world, the ability to deliver and detect radiation at different polarizations could be useful in terahertz microscopy and material characterization. In communications, polarized beams can enable multiple data streams to be sent down the same medium without interference.
“This stack-of-plates idea has advantages over traditional methods of manipulating polarization in the terahertz region,” said Dan Mittleman, a professor in Brown’s School of Engineering and senior author of a research paper describing the work in the journal Scientific Reports. “It’s cheaper and physically more robust than other methods, and it’s more versatile in what it allows us to do.”
Rajind Mendis, a research assistant professor at Brown, led the work along with Mittleman, Brown graduate student Wei Zhang and Masaya Nagai, an associate professor at Osaka University in Japan.
The terahertz range is the swath of the electromagnetic spectrum between microwave and infrared frequencies. Use of terahertz waves in technological applications such as spectroscopy, sensing, imaging and ultra-high-bandwidth communications is growing, and researchers are working to develop the hardware components necessary to build these advanced terahertz systems.
Polarization refers to the orientation of an electromagnetic wave’s peaks and valleys as the wave propagates. If a wave is propagating toward you, the peaks and valleys can be oriented vertically, horizontally or anywhere in between.
“Polarization is one of the key properties of any electromagnetic wave,” Mittleman said. “Being able to manipulate polarization — to measure it or to change it — is one of the important capabilities you need in any electromagnetic system.”
In the visible light realm, for example, manipulating polarization is used to create modern 3-D movies and to make sunglasses that reduce the glare of reflected light. Polarizing sunglasses are made by arranging polymer strands horizontally within lenses like bars on a jail cell. Those strands allow light that’s polarized vertically to pass through, while blocking horizontally polarized light, which is the dominant polarization state of light reflected off shiny surfaces like cars and water.
Existing methods of manipulating polarization in the terahertz range are very similar to the technique used in polarizing sunglasses, albeit scaled to the much longer wavelengths of terahertz light compared to visible light. Polarizing filters for terahertz are generally an array of metal wires a few microns in diameter and spaced several microns apart.
The new technique the Brown and Osaka team developed replaces the wires with a stack of closely-spaced steel plates. Each pair of plates forms what’s known as a parallel-plate waveguide. When terahertz light is shined on the stack at a 45-degree angle, it splits the beam by exciting two waveguide modes. One beam of vertically polarized light passes straight through the device, while another beam of horizontally polarized light is reflected in a 90-degree angle from the original beam axis.
The new device uses waveguides to separate terahertz radiation according to polarization state. Mittleman lab / Brown University
The technique has a number of advantages over traditional wire filters, the researchers say. The stack-of-plates architecture, which is knows as an “artificial dielectric,” is easy to make, and the materials are inexpensive. The plates are also much less fragile than wires.
“The artificial-dielectric concept also makes the device more versatile,” Mendis said. “The device can be easily tuned for use at different terahertz frequencies simply by changing the size of the spacers separating the plates or by changing the illuminating angle.”
Another advantage is that with the addition of a second similar artificial-dielectric structure, the researchers were able to build a device called an isolator. Isolators are used on high-powered lasers to prevent light from being reflected back into a laser emitter, which could destabilize or even damage it. A terahertz isolator could be an important component for future high-powered terahertz devices.
The Brown and Osaka team is in the process of patenting the new artificial-dielectric devices, and the researchers are hopeful that these devices will enable the development of new terahertz systems with far better capabilities.
“In anything you might want to do with an optical system, it’s useful to be able to manipulate polarization,” Mittleman said. “This is a simple, efficient, effective and versatile way to do that.”
The work was supported in part by the National Science Foundation (EPMD #1609521).
We introduce a sample cell that can be used for pressure-dependent terahertz time-domain spectroscopy. Compared with traditional far-IR spectroscopy with a diamond anvil cell, the larger aperture permits measurements down to much lower frequencies as low as 3.3 cm−1 (0.1 THz), giving access to new spectroscopic results. The pressure tuning range reaches up to 34.4 MPa, while the temperature range is from 100 to 473 K. With this large range of tuning parameters, we are able to map out phase diagrams of materials based on their THz spectrum, as well as to track the changing of the THz spectrum within a single phase as a function of temperature and pressure. Pressure-dependent THz-TDS results for nitrogen and R-camphor are shown as an example.
We proposed a novel planar terahertz (THz) plasmonic waveguide with folded stub arrays to achieve excellent terahertz propagation performance with tight field confinement and compact size based on the concept of spoof surface plasmon polaritons (spoof SPPs). It is found that the waveguide propagation characteristics can be directly manipulated by increasing the length of the folded stubs without increasing its lateral dimension, which exhibits much lower asymptotic frequency of the dispersion relation and even tighter terahertz field confinement than conventional plasmonic waveguides with rectangular stub arrays. Based on this waveguiding scheme, a terahertz concentrator with gradual step-length folded stubs is proposed to achieve high terahertz field enhancement, and an enhancement factor greater than 20 is demonstrated. This work offers a new perspective on very confined terahertz propagation and concentration, which may have promising potential applications in various integrated terahertz plasmonic circuits and devices, terahertz sensing and terahertz nonlinear optics.
