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Applications: Metrology
Published in David A. Cardwell, David C. Larbalestier, Aleksander I. Braginski, Handbook of Superconductivity, 2022
John Gallop, Ling Hao, Alain Rüfenacht
For conventional metallic superconductors such as Nb the energy gap is around 1.7 meV, corresponding to an upper frequency for mixing of around 3.5 THz. Ultra-high harmonic mixers of this type have been used in national standards laboratories to provide direct mixing of a microwave source with a far-infrared laser such as an HCN laser at 891 GHz as the first step in a multiplication scheme that allows the frequency of a narrow-band visible laser of known wavelength to be compared with that of a Cs atomic clock. These measurements led to a precise determination of the speed of light c and subsequently to the redefinition of the meter in terms of c and the unit of time.
Comparison of Two Learning Networks for Time Series Prediction
Published in Takushi Tanaka, Setsuo Ohsuga, Moonis Ali, Industrial and Engineering Applications of Artificial Intelligence and Expert Systems, 2022
Daniel Nikovski, Mehdi Zargham
Benchmarking of nonlinear time series prediction methods requires test problems that are representative of the problems commonly encountered in practice. Such nonlinear time series have been provided by the organizers of the Santa Fe Institute competition in time series prediction [GW94]. We used as test problem one of these time series, consisting of output of a CH3 far-infrared laser. This nonlinear chaotic time series has been predicted successfully with a locally linear model by Sauer [Sau94] and with a time-delay neural network by Wan [Wan94]. Wan used an embedding dimension of 8; this value for the dimensionality of the embedding space was adopted in our experiments too, which means that our networks had 8 inputs each. The original data were measured as integers in the range from 0 to 255, which introduces quantization error of about 0.2%.
Transients and Instabilities in FIR Lasers
Published in Peter K. Cheo, Handbook of Molecular Lasers, 2018
Pierre Glorieux, Didier Dangoisse
To answer these questions, this chapter is organized as follows. The principles of operation of a far-infrared laser are given in Sec. 8.2, where the different situations are presented. The long-time transient associated with the vibrational bottleneck effect is discussed in Sec. 8.3. In Sec. 8.4 we proceed further in the theoretical description of the laser and provide a background for Secs. 8.5 and 8.6, in which the laser transients are investigated either in a two-level model, which is shown to provide a valid description of the buildup of laser action, or in a three-level model, which is required to describe the laser switch-off. Finally, the situations in which no stable steady state corresponds to the operating conditions are considered in Sec. 8.7.
Investigation on nonlinear optical properties of symmetric and asymmetric double V-shaped AlxGa1-xAs/GaAs potential wells with structural parameters and external electromagnetic fields
Published in Philosophical Magazine, 2023
Low-dimensional semiconductor quantum systems present stronger nonlinear optical features than bulk materials [1–5]. Quantum confinement of charge carriers in a restricted region plays a key role in this. Improvements in the growth techniques of low-dimensional heterostructures made it possible to produce desired potential configurations. Parallel to practical progress, many experimental and theoretical studies on the electronic and optical properties have been performed for various forms of potential profiles. As is well known, the configuration of the potential shapes the electronic and related optical properties by determining the quantum confinement strength. Furthermore, manipulations on the potentials via the structural parameters or application of external fields serve to achieve an extended range of optoelectronic features [1–10]. Photo-detectors, transistors, electro-optical modulators, far-infrared laser amplifiers and optical switches are examples of optoelectronic devices.
A full-dimensional ab initio potential energy surface and rovibrational energies of the Ar–HF complex
Published in Molecular Physics, 2018
Jing Huang, Yanzi Zhou, Daiqian Xie
The van der Waals complex Ar–HF is one of the prototypes for studying the weak intermolecular forces between atoms and molecules during collisions [1]. The microwave, infrared and far-infrared spectra for Ar–HF have been observed through molecular beam electronic resonance spectroscopy [2], pulsed Fourier transform microwave spectroscopy [3], difference frequency laser spectroscopy [4–8], optothermal molecular beam spectroscopy [9] and far-infrared laser spectroscopy [10]. These experimental data of spectra throw light on the nature of the intermolecular interactions and help to judge the performance of the intermolecular potential energy surface (IPES) for this complex [11].
Carbon nanotube-based, serially connected terahertz sensor with enhanced thermal and optical efficiencies
Published in Science and Technology of Advanced Materials, 2022
Daichi Suzuki, Yuma Takida, Yukio Kawano, Hiroaki Minamide, Nao Terasaki
The CNT dispersion was purchased from ZEON Corporation. The physical properties of the CNTs were as follows: super-growth single-walled, metallic-semiconducting mixed, electrical conductivity of 500 S cm−1, and a Seebeck coefficient of 60 µV K−1 (pristine) and −60 µV K−1 (n-doped). The CNT dispersion was filtered through polyvinylidene difluoride membrane filters (thickness: 125 µm; pore size: 0.1 µm) and subsequently transferred onto a polyimide film. The thickness of the CNT film was measured using confocal laser microscopy (VK-X1000/1050, KEYENCE CORPORATION) (see the Supplemental material for the height profile of the CNT film). The CNT film was processed into various shapes (device and antenna) using the laser ablation method (Figure 2) [38]. The laser setup was as follows: the pulse width, wavelength, numerical aperture of the objective lenses, repetition rate, fluence, and overlap ratio were 3 ns, 532 nm, 0.3, 1 kHz, 1 J cm−2, and 85%, respectively. The n-doping solution (a mixture of potassium hydroxide and benzo-18-crown-6-ether, 0.5 mol L−1) was used to form a p-n junction in the CNT film [39]. Gold (Au) lead electrodes were evaporated using a vacuum evaporator. THz waves were irradiated at the p-n junction of the CNT film and the PTE voltage was measured using a multimeter. We prepared three types of emitters: a far-infrared laser (FIRL-100, Edinburgh Instruments Ltd.) for 1.4 THz illumination, an injection-seeded terahertz parametric generator (is-TPG) for 1–2.8 THz illumination (see the Supplemental material for the system and power spectrum) [40–42], and an infrared light-emitting diode (L14336–0083 R, Hamamatsu Photonics K.K.) for 361 THz illumination.