Applied Physics B最新文献

Propellant tanks typically operate under low-temperature and high-pressure conditions. However, existing fiber optic sensors often fail to meet the comprehensive and reliable assessment requirements for large-range strain measurements and mechanical performance in such extreme environments. To address this challenge, two types of metallized-packaged fiber Bragg gratings (FBGs) strain sensors were designed and fabricated, demonstrating exceptional suitability for high-precision localized and long-term strain monitoring at ultra-low temperatures. The FBGs were inscribed using a femtosecond laser line-by-line method and securely bonded to a metallic substrate with tin (Sn) solder, ensuring robust strain transfer and enhanced mechanical stability during cryogenic testing. Experimental results demonstrated that the FBG temperature sensors effectively performed temperature sensing in the ultra-low temperature liquid helium (LH) environment (5 K). To evaluate the mechanical performance of the FBG strain sensors in the LH environment, a cyclic load test of 1000 N was first conducted, followed by four overload tests with maximum loads reaching 3000 N. Experimental results demonstrated that the metallized FBG strain sensors exhibited a well-defined elastic region under loads up to 2500 N, characterized by a strain sensitivity of over 1.26 pm/N, and a hysteresis error less than 0.1 nm. Beyond 2500 N, the sensors transitioned into a plastic deformation regime, with the hysteresis error increasing to more than 1.47 nm.

Raman spectroscopy, widely applied to probe phonon dynamics in nanomaterials, is often considered non-destructive; however, localized laser-driven heating may significantly affect vibrational and structural responses in thermally sensitive systems. We present a systematic Raman spectroscopic study of laser-driven nanostructuring, phase evolution, and surface optical-phonon behavior in ZnO/MnO nanocomposites over a broad range of MnO concentrations (5–95%). Laser power density was varied, from 159 to 955 kW/cm², during Raman measurements to evaluate its influence on phonon behavior and phase stability. A critical laser power threshold of 40 mW (637 kW/cm²) was identified at 30% MnO concentration, where a Raman mode near 258 cm⁻¹ splits into two components, providing direct spectroscopic evidence of this phase transition involving MnO-related intermediate phases. At higher manganese concentrations, the Raman response reveals a complex coexistence and evolution of manganese-related phases, including MnO, Mn₂O₃, MnO₂, MnOOH, Mn₃O₄, ZnMn₂O₄, and ZnMnO₃. Surface-related vibrational modes progressively weaken and disappear with increasing manganese content and laser power, indicating a transition from zinc oxide to manganese oxide-dominated structures. These findings highlight the decisive role of laser excitation conditions in Raman spectroscopy and provide practical guidance for interpreting measurements of thermally sensitive mixed-oxide nanomaterials.

Optical vortices can be generated periodically across an interference region when three or more coherent waves interact, forming an optical vortex array (OVA). In this work, we investigate how the initial topological charge (TC) of the incident beam is redistributed among the phase singularities formed in the interference field by interfering a Laguerre-Gaussian beam carrying orbital angular momentum (OAM) of ± l with two Gaussian beams, while the total TC remains constant. We demonstrate that, for a zero-order vortex beam (l = 0), the interference results in paired vortices carrying opposite unit TCs of ± 1, whereas for nonzero TCs (l > 0), the original TC does not remain localized in a single higher-order vortex but instead undergoes a systematic splitting into l individual unpaired vortices, each carrying a unit TC of + 1. For fractional TC, the number of unpaired vortices follows a nearest integer rule of the imposed TC, exhibiting n unpaired vortices for fractional charges closer to the integer n and n + 1 unpaired vortices as the charge approaches the next higher integer. The reported results are supported by numerical simulations and experimental verification, providing new insight into optical vortex formation and enabling controlled vortex engineering with potential applications in optical trapping and manipulation, high-dimensional optical communication, and structured-light-based information encoding.

Dielectric Barrier Discharge (DBD) excimer lamps emitting at 222 nm are promising for sterilization due to strong antimicrobial activity and reduced risks to human health. Unlike conventional 254 nm mercury lamps, Far-UVC at 222 nm penetrates microorganisms but not living human cells, enabling safe use in occupied spaces. This study reports the design and fabrication of optical thin-film filters that selectively transmit 222 nm radiation while blocking harmful 254 nm light. Filters were designed with OpenFilters software and deposited on quartz substrates using 2-inch magnetron sputtering. The multilayer structure of Si₃N₄, Al, and SiO₂ showed ~ 7% transmittance at 222 nm with complete blocking at 254 nm. Microbiological experiments were performed using a KrCl₂ excimer lamp operated with and without the filter. For Escherichia coli, the filtered lamp achieved log reductions of up to 1.47 after 45 min, while the unfiltered lamp produced reductions exceeding 4 log under identical conditions. Similar trends were observed for Staphylococcus aureus. Although reduced microbial inactivation was observed with the filtered system, the effective suppression of hazardous wavelengths demonstrates its potential for safer Far-UVC disinfection. These results highlight the role of 222 nm band-pass filters in improving the safety and applicability of DBD excimer lamps for UV sterilization.

Continuous-wave (CW) cyan and deep-ultraviolet lasers at 488 nm and 244 nm were realized using a Pr³⁺:YLF crystal. A folded V-type resonator with a Brewster-angle birefringent plate generate single-line oscillation at 488 nm, producing a maximum output power of 342 mW under 15 W diode pumping. Intracavity frequency doubling with a 3-mm BBO crystal generates 244 nm radiation, achieving 62 mW of output. This work represents the first demonstration of CW Pr³⁺:YLF laser emission at 488 nm and its extension to 244 nm, offering a compact approach for blue-cyan and deep-UV sources.

In this work, the vectorial vortex beam generation is presented to support the dynamic control of the structured light. The principle of phase stitching is implanted for the preparation of phase holograms. The single-phase hologram containing different topological charges in the upper and lower half is designed to introduce the asymmetrical geometry of vortex beam. The conversion from asymmetrical to symmetrical is controlled through topological charge. This grated method is implemented first to the spiral phase and coherently added to the axicon, termed as grafted spiral axicon. The spatial rotation of vortices of the plane polarized vortex beam is obtained after analyzer transmission. The vortices that appear on the upper and lower half of a ring are moved along the circle either in the same direction or opposite direction. The vortices introduced in the concentric rings and mutual controllable rotation along clockwise or anticlockwise to extend the family of vortex beam. This controllable generation of bright lobes and spatially rotating of these lobes of the vortex beam is termed as vectorial vortex beam. This technique can be applied where the asymmetrical distribution of particles is present and secondly, where the dynamic spatial control of lobes is required.

The nonlinear process of spontaneous parametric down-conversion in the silver-gallium-sulfide crystal can generate highly non-degenerate photon pairs in near-infrared and mid-infrared spectral ranges. In this work, we demonstrate and characterize the tunable mid-infrared photon source in silver-gallium-sulfide. By angle tuning the phase matching condition of the nonlinear crystal, we can tune the wavelength of the generated photons in mid-infrared from 5.661 to 10.885 μm (from 1766 to 919 cm⁻¹), while the correlated photons in the near-infrared are from 747.1 to 702.6 nm. The phase matching curve and the frequency-angular spectrum of mid-infrared photons were experimentally validated by measuring the properties of near-infrared photons. The brightness of the photon pair source was found to be (29.2± 1.1)(frac{text{MHz}}{text{mW}}) in the low-gain regime, exceeding the values reported in previous studies using silver-gallium-sulfide crystals. The wide tunability of the photon source in the mid-infrared range is important for hyperspectral imaging and sensing, and it is of significant interest for biomedical, chemical, and environmental applications.

In this study, we explore a novel approach to accelerating electrons by utilizing Bessel beam generated from an axicon lens alongside an externally applied wiggler magnetic field. Bessel beams are unique in their ability to maintain a non-diffracting profile over long distances, making them ideal for the efficient acceleration of electrons. The axicon lens converts a conventional Gaussian beam into a Bessel beam, creating a central bright spot surrounded by concentric rings, which enhances the stability of the interaction. Among the various orders of Bessel beam, the zeroth-order beam is especially advantageous due to its lower divergence and stronger focusing capabilities, leading to more efficient electron acceleration compared to higher-order beams. By utilizing the characteristics of zeroth-order Bessel beam and the oscillating effects of the wiggler magnetic field, we investigate the energy gain and trajectory modulation of electrons in this system. Our findings demonstrate that the presence of the wiggler field significantly enhances the focusing power of Bessel beam, resulting in enhanced acceleration rates compared to a fundamental Gaussian beam under identical conditions.

Manufacturing imperfections in large-aperture holographic gratings critically limit multi-petawatt Chirped Pulse Amplification systems. This study investigates their impact on wavefront quality using Zemax ray-tracing simulations based on real interferometric measurements. The results confirm that distortions are cumulative, with imperfections in the second and third gratings primarily driving beam degradation. Significantly, we demonstrate that rotating these critical gratings by 180° alters the residual wavefront structure. The study concludes that optimizing grating orientation, combined with adaptive optics, is an effective strategy to mitigate aberrations and restore peak intensity, offering vital guidelines for next-generation high-field laser facilities.

A non-contact method for assessing the local geometrical thickness, porosity, and effective refractive index of synthetic opals using spectral optical coherence tomography is proposed. This approach was employed to investigate the diffusion of aqueous glycerol solutions with varying concentrations into the macropores of synthetic opals pre-filled with water. The kinetics of changes in the optical thickness and refractive index of synthetic opals during the optical clearing process were monitored. The obtained data were analyzed using the least-squares method, which enabled the determination of porosity 20–30%, refractive index 1.37–1.45, and geometrical thickness 0.94–1.17 mm of the synthetic opals. The results were validated by an alternative method of refractive index matching. It is demonstrated that the proposed approach can be applied to the analysis of local structural and optical parameters of porous materials, offering promising prospects for applications in materials science and bioengineering.