All-dielectric binary gratings, with and without slab waveguides, are designed to generate polarization-independent guided-mode resonance filters (GMRFs) operating in the THz frequency region using ...the rigorous coupled-wave analysis (RCWA) method. The filling factor and thickness of the grating were adjusted to have equal resonance frequencies of transverse electric (TE)- and transverse magnetic (TM)-polarized THz beams. The single polarization-independent resonance for a binary grating without a slab waveguide was obtained at 0.459 THz with full width at half maximum (FWHM) values of 8.3 and 8.5 GHz for the TE and TM modes, respectively. Moreover, double-layered polarization-independent resonances for binary gratings with slab waveguides were obtained at 0.369 and 0.442 THz with very high Q-factors of up to 284. This is the first study to propose a polarization-independent GMRF with two resonant frequencies.
In this paper, we propose a terahertz (THz) guided-mode resonance (GMR) notch filter made of a monolithic polyethylene terephthalate (PET) film, which has a monolayer grating structure. The proposed ...configuration shows both polarization-dependent and polarization-independent notch filter characteristics for the incident THz wave depending on the rotation angle of the second grating film. When the rotation angle is 0°, the filtering strength (transmittance) at resonance frequency changes from 0.4 (0.996) to 99.0% (0.010) according to the incident polarization. The transmittance continuously decreases with increasing rotation angle until 90°. When the rotation angle is 90°, the transmittance converges to 0.065 (± 0.015) independent of the incident wave polarization. When the incident polarization angle ranges from 90° to 180°, paradoxically, the transmittance through the two GMR grating films is greater than the transmittance through only the first GMR grating film due to the enhancement of the vertical component of the THz wave. These results agree well with a calculation using a polar coordinate system.
Abstract
The deflection of charged particles is an intuitive way to visualize an electromagnetic oscillation of coherent light. Here, we present a real-time ultrafast oscilloscope for time-frozen ...visualization of a terahertz (THz) optical wave by probing light-driven motion of relativistic electrons. We found the unique condition of subwavelength metal slit waveguide for preserving the distortion-free optical waveform during its propagation. Momentary stamping of the wave, transversely travelling inside a metal slit, on an ultrashort wide electron bunch enables the single-shot recording of an ultrafast optical waveform. As a proof-of-concept experiment, we successfully demonstrated to capture the entire field oscillation of a THz pulse with a sampling rate of 75.7 TS/s. Owing to the use of transversely-wide and longitudinally-short electron bunch and transversely travelling wave, the proposed “single-shot oscilloscope” will open up new avenue for developing the real-time petahertz (PHz) metrology.
Free electron lasers (FELs) have been highly anticipated as a new light source since they were developed in the 1970s because of their perfect wavelength tunability and high power potential. Various ...types of FELs have been developed over a wide range of wavelengths from mm waves to X-rays, and many technological advances have been made for devices and applications. In particular, X-ray free-electron lasers (XFELs), the fourth-generation synchrotron, have made a great contribution to the deep understanding of matter and nature. However, there have been relatively few advancements in industrial technology using FELs; for example, an FEL has not yet been directly used in the field. High-power light sources in the terahertz (THz) wavelength range are in high demand in industry and the field but have not been properly developed. The FEL is the most powerful light source in the THz range, and although the size of these FELs is still large, they have the spectral range with the greatest potential for industrial or field applications. This study examines the potential of compact THz FEL technology to meet market needs. The current status of various elements of the FEL is reviewed, and the prospects of a possible FEL system are described by combining these elements. An FEL system with an average power of 1 W operating in the THz center wavelength range of 300–600 μm is expected to be realized in an FEL with a size of 1.5 m × 2 m.
In this paper, floating fin structured vertically stacked nanosheet gate-all-around (GAA) metal oxide semiconductor field-effect transistor (FNS) is proposed for low power logic device applications. ...To verify the electrical performance of the proposed device, three-dimensional (3-D) technology computer-aided design (TCAD) device/circuit simulations are performed with calibrated device model parameters. As a result, it is found that gate propagation delay (tdelay) and dynamic power (Pdyn) are improved by 8% and 19%. respectively as compared to conventional vertically stacked lateral nanosheet (LNS). Through the rigorous analysis on the resistance and capacitance components of FNS and LNS, it is clearly revealed that the τdelay and Pdyn are improved at the same Pdyn (50 μW) and tdelay (187 GHz) by the reduced effective capacitance which results from the diminished gate-to-sorece/drain overlap area. Based on the TCAD simulation studies, it is expected that the FNS is suitable for next generation logic digital applications.
The ferroelectric-metal field-effect transistor with recessed channel (RC-FeMFET) is proposed for one transistor dynamic random-access memory (1T-DRAM). Through technology computer-aided design ...(TCAD) simulations, the effects of inter-metal insertion on the FeFET with recessed channel (RC-FeFET) is identified. By evaluating electric field (e-field) across interlayer (IL) and memory window (MW), the improvements of program/erase cycling endurance and read current sensing margin (RSM) are verified in the RC-FeMFET. Moreover, considering program voltage (V W ) and polarization switching time (<inline-formula> <tex-math notation="LaTeX">\tau _{\mathrm{ p}} </tex-math></inline-formula>), the guide line of the RC-FeMFET design is provided in terms of e-field across IL and MW for 1T-DRAM applications.
There are difficulties in developing high-power and small-size terahertz (THz) sources that can be used for field applications. In an attempt to design small-size THz free-electron laser (FEL) ...devices capable of producing higher output powers in the THz spectral region of 1–2 THz, we have developed a microtron accelerator that can accelerate electron beams to 3–6 meV, with a macropulse current of more than 40 mA. The new THz FELs use hybrid electromagnetic (EM) undulators that are two to four times shorter in length than the previous undulator and waveguide resonators with mode cross-sectional areas that are more than two times smaller than the parallel-plate waveguide in the existing FEL. We confirm that the gains and losses of the compact FELs are sufficient for lasing, and we estimate that average output power of approximately 1 W is possible with an efficiency approximately 10 times greater than the existing FEL. The minimum size of the THz FEL system, including a high-voltage pulse modulator, is estimated to be approximately 1.5 m × 2.0 m.
In this paper, we report the structural dynamics of polycrystalline bismuth (Bi) thin films in response to photoexcitation, visualized by mega-electron-volt ultrafast electron diffraction. The data ...reveal that the carrier–phonon scattering process involves phonon squeezing within sub-picoseconds (ps) and lattice thermalization within a few ps. Through the time-resolved pair distribution function analysis, we directly observe the changes in the interatomic distance of adjacent Bi atoms in real space, which can be explained by phonon softening and subsequent phonon squeezing.
In a laser-plasma electron acceleration, the quality of electron beams is sensitive to the parameters of a laser and a plasma density. With a given laser, higher plasma density may be good for higher ...charge, while lower density is better for longer acceleration channel, generating higher peak energy at the expense of charge. The dependence of electron beam parameters on the plasma density is, therefore, crucial to find the operating condition for applications. After the target chamber is evacuated, the plasma density and the focal position of the laser beam in the plasma channel can be remotely controlled during the experiments. The plasma density can be obtained by extracting the phase information from captured interferogram, followed by numerically computing the integral derived using Abel inversion. We suggested the simple idea of FFT Filtering and Reconstructing (FR), to be processed prior to a typical computing process, which is the continuous wavelet transform (CWT) for phase shift and the Fourier–Hankel transform (FH) for the integral of Abel inversion here. The FFT filtering can suppress the errors due to the noise, while the reconstructing can select the different data points between the fringes to reduce the systematic error and improve the visibility in interferograms. We confirm the FR-CWT-FH method can provide the average plasma density in uniform region and the longitudinal channel structure with high accuracy, letting the in-situ monitoring possible. The fringe spacing in reconstruction and the wavelet frequency in CWT can be selected differently depending on the shape of plasma density, such as uniform or rising (or falling), and its length of each region to obtain the detailed structure of plasmas.
Carbon ions and protons from a double-layer target, a copper foil coated with a polymer exhibit non-Maxwellian spectral shapes, when an ultra-intense laser pulse with a high temporal contrast ratio ...was focused on the metal side of the target. The spectral shapes, showing strong reduction of low-energy ions, a high-energy island, and a modulated structure, are different from a typical thermal distribution usually obtained from a pure metal target in the laser acceleration of ions. In the case of C
6
+
ion, a high-energy island with an energy spread of 0.5 MeV/u was observed, which is separated from the low-energy spectrum by 0.2 MeV/u. A modulation in the proton energy spectrum was observed, which leads to a secondary peak at 2.2 MeV/u in addition to a peak at a low energy of 1.5 MeV/u. The maximum energy obtained from the double-layer target at a laser intensity of 3
×
10
20
W/cm
2
is 3.4 MeV/u for C
6
+
ions and 10 MeV/u for protons, which are higher than those obtained from a single metal foil by factors of 1.7 and 1.3, respectively. Such a spectral shape and energy enhancement could be accounted for by a bulk electrostatic field formed at the metal-polymer interface and multi-species interactions. These results show that the spectral shape of the ion beam can be tailored with an adequate structure of micrometer-thick target.
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