We discuss some problems of microwave modulation of terahertz radiation emitted by quantum cascade lasers. The propagation of electromagnetic waves inside the cavities of terahertz quantum cascade lasers (THz QCLs) made of Al0.15Ga0.85As/GaAs with a double metal waveguide and a variable cavity length of 0.5 to 3.0 mm in the frequency range 0.1–67 GHz was experimentally studied. In addition, the effect of shifting the microwave probe from the cavity edge was analyzed. Good agreement between the experimental results and the simulated field distribution in the cavities was obtained. The complex refractive index n of the active medium in the THz QCL cavities of Al0.15Ga0.85As/GaAs was estimated in the frequency range 10–70 GHz: Re [n(f)] = 3.78–3.23 at frequencies of 10 to 40 GHz and does not change at 40 to 70 GHz; Im [n(f)] = 2.00–0.35. The obtained information is of great importance for gigahertz modulation of the THz QCL injection current to achieve the mode-locking regime.
Implementation of artificial neural networks on classical computer architecture is inefficient due to high energy consumption. Further development in the field of artificial intelligence requires that new hardware platforms for creating neuromorphic elements should be found. In this paper, we demonstrate a subterahertz integrated Mach–Zehnder interferometer with a phase shifter, which will become the main component of the element base for constructing artificial neural networks designed to solve the problem of channel search and estimation in future 6G communication systems.
We develop an optical amplifier of a telecommunication signal in the C-band based on a polymer single-mode waveguide with the incorporated nanoparticles displaying Stokes luminescence. For this purpose nanoparticles α-NaYbF4:Er3+,Ce3+@NaYF4 with the core-inert shell structure and an average diameter of 30 nm have been synthesized. The nanoparticles exhibit intense luminescence in the range of 1530–1565 nm when excited by near infrared light with the wavelength of 980 nm. A polymer waveguide amplifier containing nanoparticles in a concentration of 0.05 wt
We study hydrogen-bonded (CX3)2O···HF (with X= H, D) complexes that play an important role in intermolecular interactions in the gas and liquid phases. We investigate the vibrational and rotational characteristics of these complexes using infrared spectroscopy, density functional theory (DFT) calculations, and topological analysis methods, including atoms in molecules (AIM), noncovalent interactions (NCI), and reduced density gradient (RDG). Infrared spectroscopic measurements were conducted at 188 K with a Bruker IFS-120 HR vacuum Fourier transform spectrometer. The data obtained revealed significant red shifts in the HF stretching frequencies due to hydrogen bonding. The DFT calculations at the B3LYP/6-311++G(d,p) level confirm the structural rearrangement and frequency shifts upon complex formation. The calculated vibrational frequencies agree well with the experimental data. This agreement confirms the reliability of the chosen theoretical approach. The AIM, NCI, and RDG analyses provide a detailed characterization of the hydrogen bond in (CX3)2O···HF. The bond critical point analysis indicates a strong electrostatic interaction, while NCI and RDG results confirm the contribution of dispersion forces to the overall stability of the complex. This study enhances our understanding of hydrogen-bonded complexes, offering insights into their spectroscopic properties and structural dynamics. The findings contribute to a deeper comprehension of hydrogen bonding mechanisms in various molecular environments.
We establish the physical mechanism of the long-wavelength spectral shift during the propagation of an ultraviolet femtosecond pulse in gases using a numerical solution of the non-stationary Schrödinger equation. It is shown that the source of long-wavelength radiation is the leading edge of the pulse, where a cubic response delayed by approximately 100 as develops with a nearly zero phase shift between the polarization and the pump field. It was established that the long-wavelength shift of the spectrum arises due to the superposition of contributions from bound-bound and bound-free transitions.
