Bulletin of the Russian Academy of Sciences: Physics最新文献

Advanced characterization of 3D microstructures is critical for applications in optics, photonics, and biomedicine. Confocal laser scanning microscopy (CLSM) has emerged as a key technique for non-destructively characterizing microstructures fabricated via direct laser writing (DLW) lithography. CLSM offers high resolution and contrast scanning, simplified sample preparation and easy to operate, as well as lower cost compared to electron microscopy. In addition, CLSM allows rapid acquisition of longitudinal and cross-sectional images at any position in 3D microstructures. This review summarises recent CLSM applications for investigation of fabricated DLW microstructures. We discuss CLSM approaches for visualising internal microstructures, surface analysis, and the investigation of material properties. Furthermore, we discuss the utilization of CLSM in case studies of fabricated DLW microstructures for different applications. Finally, we provide our thoughts on future directions for CLSM integration with advanced fabrication techniques to expand characterization capabilities. Hence, we hope that this review will provide a fruitful insight for research communities in optical engineering, photonics, and materials science.

We studied fluid flows in evaporating sessile ethanol droplets subjected to heating by CW laser radiation via the light-absorbing substrate. The flow dynamics under the combined effect of evaporative cooling and localized laser heating were investigated using a fully coupled nonisothermal flow finite element model incorporating the arbitrary Lagrangian–Eulerian moving mesh methodology to accurately capture the motion of the droplet surface due to evaporation in the constant contact angle mode. The competition between Marangoni flows driven by these two thermal mechanisms and the resulting control over the flow pattern, average temperature and droplet evaporation time is elucidated. It is shown that flow switching to the laser-induced circulation pattern is characterized by flow velocities more than an order of magnitude faster than the pre-laser state. This flow reorganization significantly increased the droplet’s average temperature and drastically reduced the total evaporation time. The findings of the study provide new foundations for active control of droplet dynamics in microfluidic and coating technologies.

We studied the methods for measuring propagation losses in thin-film lithium niobate (TFLN) waveguides. Thin-film lithium niobate is a promising platform for integrated photonics, enabling the fabrication of compact waveguide structures and topologies. The fabrication process of TFLN waveguides includes several stages: design, fabrication, and testing. This paper focuses on the testing stage, which allows for an objective evaluation of the fabrication process and the correctness of the design. The methodology for measuring propagation losses in waveguides is an important research topic in integrated photonics. Several measurement approaches are considered, including interferometric methods based on Fabry–Pérot resonances within the waveguide and the cut-back method. A comparison of these methods in terms of universality, repeatability, and accuracy shows that the cut-back method is the most promising among those considered.

The influence of high hydrostatic pressure and powder annealing temperature on the sintering kinetics of Al₂O₃ was investigated. Dilatometry revealed that the sintering of metastable aluminum oxide phases occurs in two stages, with densification inhibition between these stages. It was shown that the use of metastable γ/θ-Al₂O₃ phases along with a pressure of 700 MPa reduces the temperature required to obtain high-density corundum ceramics to ~1500–1550°C.

We have explored germanium nanoparticles (Ge NPs) as a potential material for photothermal therapy in cancer treatment. Given the high intrinsic optical absorption of bulk germanium in the near-infrared (NIR-I) biological transparency window, pulsed laser ablation in liquid (PLAL) was employed to produce a colloid of Ge NPs with a Mie-resonant size in the range of 100–500 nm. The heating efficiency of individual Ge NPs was evaluated using 785 nm laser irradiation, while the temperature-dependent shift in the Ge–Ge Raman band was monitored simultaneously. The maximum estimated temperature increase of 480 K at a laser power density of 3 mW/μm² for Ge NPs with a diameter of 300 nm was confirmed with no signs of oxidation or structural degradation. This value is more than four times higher than that of pure silicon NPs of a similar size. Laser heating (808 nm, 4.5 W) of an isopropanol suspension containing Ge NPs demonstrated that their resonant size enables grounds for mild photothermal therapy with a linear light-to-heat conversion efficiency response to NPs concentration reaching 17%, and the potential to heat the suspension by ∆T = 5–50°C within an NPs concentration range of 1.25–10 μg/mL.

The problem of low efficiency of power supply systems with energy transmission over optical fiber (Power-over-Fiber, PoF), belonging to the class of optoelectronic devices and systems, is investigated. It is shown that a significant decrease in efficiency occurs in the dynamic mode of operation under varying complex load. To solve this problem, a method based on the use of pulse-width modulation (PWM) of the laser diode pump current is proposed. This method allows maintaining high efficiency of the key system components even when operating at low average power levels. Computer simulation of the system was carried out in the MATLAB Simulink environment using digital twins. It is shown that the transition to the pulsed mode increases the system efficiency by 1–6% in the average optical power range of 0.75–15 W compared to the continuous mode, leveling its value to 12–14% over the entire operating range. The proposed method improves the efficiency and reliability of advanced optoelectronic systems for remote sensing, monitoring, and power supply in challenging electromagnetic and temperature conditions.

We report a single‑step, maskless route to fabricate palladium patterns directly on silicon using ultrashort‑pulse laser writing under a Pd‑salt solution. Varying the precursor concentration controls the morphology over a broad range. At ~10⁻⁶ M, the substrate shows subwavelength ripples characteristic of laser‑induced periodic surface structures (LIPSS) with no detectable Pd. At higher concentrations, the ripples become decorated with Pd nanoparticles, which then coalesce into continuous films that inherit the grooved relief, while at ≥10⁻³ M nanoflower‑like dendrites emerge. Arbitrary patterns (including line arrays, net‑like lattices, and dot arrays) are written with micrometer pitches and clear gaps between features. Post‑oxidation at 450°C converts Pd to PdO, as confirmed by the ~640 cm⁻¹ Raman band. These Pd and PdO structures, with tunable nanoscale morphology, offer a direct pathway to integrated optical and resistive hydrogen‑sensor elements for on‑chip leak detection and safety monitoring across hydrogen production, storage, and distribution.

The development of new synthetic approaches for realization of high-quality perovskite nanocrystals is one of perspective research directions. Generally, synthetic approaches require complex apparatus and precise parameter control to achieve high quality nanocrystals. Therefore, searching for low cost and simple approaches for fabrication of fine perovskite nanocrystals capable of demonstrating resonant properties such as lasing is one of the most difficult but promising research directions. In our approach we use polymer dendrites that offer high structural and geometrical reproducibility by growing in periodic structures. This reproducibility and periodicity can be used for fabrication of various resonant photonic structures confined inside dendrites. In our study, we demonstrate that bunches of high-quality perovskite nanocrystals can be grown inside polymer dendrites. Obtained perovskite nanocrystals preserve strict geometrical form typical for growth methods like chemical vapor deposition or solution assisted nucleation. Obtained perovskite nanocrystals under pump excitation demonstrate high-quality single mode lasing with narrow laser line.

Today, perovskite thin-film electronics require specific semiconductor materials for high performance. Modern indoor perovskite solar cells can be significantly improved if the classic MAPbI₃ semiconductor is replaced by triple-cation compositions with a band gap greater than 1.6 eV. However, simply changing the anion proportion in a perovskite can lead to changes in the Goldschmidt tolerance factor and initiate phase separation. In this study, one of the most stable CsFAMAPb(IBr)₃ thin films was used to investigate new stable compositions under UV light. Here, we used six different proportions of halogens with a fixed ratio of cations in the thin films, which were experimentally tested to determine their optical and photoluminescence parameters and assess their potential for indoor photovoltaic applications.

We present numerical calculations of the cooperative photoluminescence spectra of two dipole–dipole–coupled dibenzoterrylene molecules embedded in an anthracene crystal at liquid-helium temperature. Using master-equation formalism for non-identical two-level emitters, we reproduce the excitation spectra recently observed in experiment. The excellent agreement between the simulations, analytical model, and measurements confirms the observation of controllable molecular entanglement and validates the theoretical framework. The approach provides an efficient computational tool for predicting and controlling cooperative photoluminescence in solid-state molecular systems. These results establish a basis for future experiments aimed at achieving optical entanglement of organic molecules and developing quantum photonic devices.