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.
We present the results of an experimental study of the influence of laser pulse parameters on the energy characteristics of terahertz radiation generated during single-color filamentation in air. A two-dimensional spatial distribution of the radiation energy density was obtained, and the analysis of the indicated characteristics was carried out on the basis of integrating this distribution over the entire range of angles where the radiation was observed. It is shown that an increase in the laser pulse energy leads to an almost linear increase in the energy of terahertz radiation at all observed frequencies in a wide range of focusing. Varying the numerical aperture of the focused laser beam demonstrated the existence of an optimal value at which the energy of terahertz radiation is maximum and which is almost independent of the frequency of terahertz radiation. It is also shown that for each frequency of terahertz radiation there is a certain duration of the laser pulse at which the energy of terahertz radiation will be maximum.
The spectral sensitivity and other characteristics of the single-element pyroelectric MG-32 detector, which is manufactured by JSC Novosibirsk Semiconductor Devices Plant Vostok and is based on a 1 μm thick organic crystal of tetraaminodiphenyl, are studied in the terahertz frequency range. A polypropylene (PP) window or a polypropylene lens 10 mm in diameter with a hyperbolic surface profile was installed at the detector input. The experiments were performed with radiation from the Novosibirsk Free Electron Laser in the wavelength range λ = 164–358 μm (0.8–1.8 THz). The voltage sensitivity of the detector with the PP window was independent of the radiation wavelength, while in the experiment with the lens it decreased in inverse proportion to λ2 due to the diffraction-induced increasing of the focal spot, which was consistent with the numerical calculations using wave optics. The sensitivity of the detector with the lens is 6 to 16 times lower (depending on λ) than with the PP window. Owing to the larger aperture of the lensed detector, its detectivity is comparable to that of the detector with the PP window, and according to theoretical estimates, it can exceed this value in the short-wavelength terahertz range by a factor of tens, becoming comparable to that of a Golay cell. The results demonstrate that in the terahertz frequency range, the MG-32 detector with a modified PP window or a lens is sufficiently sensitive and the fastest among uncooled detectors. This makes it a convenient tool for various studies and applications in the field of terahertz photonics.
