Lithuanian Journal of Physics

Title

2025-12-18T13:50:55+02:00

2025-12-18T14:37:35+02:00

Subcycle vector optical pulsed bullets carrying optical angular momentum

2025-12-22T13:58:19+02:00

The generation and experimental realization of nondiffracting and nondispersive light pulses remain a diﬀicult challenge in the field of optics. Recent advances in ultrafast optics allow for the production of high-power, few-cycle pulses with a significant fluence. Applying these capabilities to nondiffracting and nondispersive beams requires a thorough mathematical framework for describing highly focused vector pulses. In this study, we investigate vector optical bullets propagating in free space and in dielectric media, considering multiple polarization states such as linear, azimuthal and radial ones. We also note the differences between the vectorial and scalar models. Furthermore, we explore various group velocities: superluminal, subluminal and negative. Special attention is given to higher-order topological charges, revealing their influence on the spatial structure and propagation dynamics of these pulses. Finally, we demonstrate the possibility of generating subcycle duration pulsed beams, both in vacuum and in dielectric material, while preserving their nondiffracting and nondispersive characteristics, and investigate their spatial intensity distributions and temporal durations while also showcasing individual component influences on the total intensities.

Nonhomogeneously polarized Airy beams and their accelerating lattices of optical quasiparticles.

2025-12-22T13:59:27+02:00

Radially polarized Airy vector beams are numerically investigated in terms of their spatial spectra, electromagnetic field distribution, and topological structure. Airy-type beams, which belong to the class of non-diffracting optical beams, are notable for their ability to propagate in a bent accelerating trajectory while reconstructing their intensity profiles even after encountering obstructions. This work analytically investigates vector beams with non-uniform, radial and azimuthal polarization distributions, which exhibit phase singularities and intensity zeros (dark spots). Additional topological features are observed, and the skyrmionic density of the electric field and the linear momentum are analyzed numerically, revealing the existence of an accelerating lattice of optical quasiparticles in the beams.

Effect of low-concentration gadolinium doping on the thermal properties of MWCNT composites.

2025-12-18T14:45:45+02:00

In this study, the thermal properties of multiwalled carbon nanotubes doped with 5 wt% gadolinium were analyzed. Thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) and transmission electron microscopy were successfully employed for material characterization. Transformations in the TGA profiles of the synthesized carbon-based nanocomposite were investigated. The specific heat capacity value of that nanocomposite was attributed to the influence of Gd doping. For gadolinium-doped MWCNTs, a Cp value of 826.4 J/(kg·K) was observed at 630.4 K. These findings highlight the potential of rare-earth-doped carbon nanomaterials for use in thermal interface materials and other heat management applications in advanced electronics and energy systems.

Modulation of viscoelasticity as a result of information reading by ultrasonic field of polyvinyl chloride–metal-nanodispersed filler system

2025-12-18T14:45:29+02:00

The results of studying the viscoelastic properties and mechanical relaxation processes of systems based on polyvinyl chloride (PVC) containing 0–3.00 vol. % of nanodispersed copper powder obtained by the physicochemical method (ph/ch) and the method of electric conductor explosion (ECE) were presented. The viscoelasticity modulation was carried out at a frequency of 0.4 MHz in the temperature range 298 K ≤ T ≤ Ts. Based on the phenomenological Maxwell–Frenkel approach, the processes of compression–tension, shear, and bulk deformation of the composite were investigated. It has been shown that the viscoelastic properties of the system are due to the structural changes, energy and entropic influence of the boundary layer (BL). The maximum changes in the value of the viscoelastic characteristics of the PVC system occur in the range of changes in the Cu content of 0.05–1.50 vol. %, which expands the scope of the material in thermal and dynamic (mechanical) fields.

Mechanical stress, optical and surface properties of high temperature annealed HfO2, Sc2O3 and Al2O3 binary mixture thin films deposited by ion beam sputtering

2025-12-18T14:45:13+02:00

High compressive stress is one of the main drawbacks of ion beam sputtered coatings by deteriorating the flatness of optical components. Mixtures of high refractive index metal oxides with SiO2 allow one to increase the laser induced damage threshold of multilayer stacks. Study of optical, surface roughness and stress properties of HfO2–Al2O3, Sc2O3–Al2O3, HfO2–Sc2O3 binary mixtures using a broad range of post-deposition thermal annealing up to 900°C is presented. Admixing Al2O3 in moderate concentrations to HfO2 and Sc2O3 allows one to sustain a low surface roughness, to decrease the extinction of layers during thermal treatment, while obtaining –360…–560 MPa tensile stress after annealing to 500°C, depending on the particular mixture. The obtained data allow one to point out possible candidates – HfO2(56%)–Al2O3(44%), Sc2O3(70%)–Al2O3(30%), HfO2(~70%)–Sc2O3(~30%) – and the 500–600°C annealing temperature range for the design of stress compensated multilayer coatings for the UV spectral range with potentially increased laser induced damage threshold.