Applied Physics B最新文献

Methods of Laguerre–Gaussian (LG) modes formation are now the content of a significant number of publications on lasers of various types. Axicons with an obtuse apex (170–178(^{circ })) in combination with spherical lenses have been traditionally used in pumping channels of solid-state lasers to produce annular pump beams for LG modes selection. Switching of modes was carried out usually by moving the lenses or some other elements of the laser. We show that acute-apex axicons in a liquid (which do not work in air because of the total internal reflection inside) can be used also for LG modes selection and allow temperature switching of modes. A cuvette with 78(^{circ }) apex axicon immersed in a liquid mixture was installed in the pumping channel of a pulsed Rh6G dye laser ((lambda _text {las} approx ) 580 nm, (lambda _text {pump}) = 532 nm). Temperature tuning of LG(_{0,l}) petal modes with indices up to l = 21 was demonstrated. Switching to the neighboring mode required changing the temperature of the cuvette with the axicon by (approx ) 1.2(^{circ }hbox {C}) with no shift of any laser elements. The obtained results expand the range of axicons that can be used in laser pumping channels and provide a practically convenient method of LG modes selection in a laser.

Optical sensor research faces significant limitations due to reliance on single-parameter measurements and scarce experimental data. This study introduces an advanced physics-based framework employing rigorous finite-difference time-domain (FDTD) simulations to analyze electromagnetic wave propagation in optical grating structures. A comprehensive dataset of 5000 simulations with 11 parameters is systematically generated, closely mimicking experimental conditions and addressing critical biosensor data gaps. Moving beyond traditional peak-wavelength analysis, multiple spectral features including FWHM, peak reflectance, and integrated spectral area are extracted using Python-based post-processing algorithms. Advanced data visualization reveals non-trivial sensitivity patterns, particularly highlighting enhanced performance for 100-nm analyte layers at n = 2.500. A machine learning (ML) approach, utilizing a multi-layer perceptron (MLP), establishes a new measurement paradigm, achieving exceptional prediction accuracy (R²=0.9992 for wavelength, 0.9546 for FWHM). This demonstrates that multi-parametric analysis significantly outperforms conventional methods. The methodology is extendable to diverse optical sensor architectures through feature engineering, and the publicly available datasets provide a foundation for future computational photonics and intelligent sensor design. This work innovatively integrates physics-based simulations, data generation/processing, advanced visualization, and ML, enabled by Python’s computational power and physical insights. In contrast to conventional AI applications in photonics that typically rely on experimental data optimization or limited numerical simulations, this study establishes a novel paradigm by integrating large-scale FDTD-generated datasets with machine learning, enabling comprehensive multi-parameter spectral analysis previously unattainable with traditional methods.

This study presents a comprehensive theoretical and numerical investigation of multiphoton absorption (MPA) in Z-scan experiments using super-Gaussian laser beams. We developed an analytical model for normalized optical transmittance under weak nonlinearity approximation and performed extensive simulations examining the effects of varying MPA absorption order and super-Gaussian beam parameter. Our results reveal that flatter beam profiles consistently produce stronger nonlinear absorption effects across all multiphoton orders due to extended high-intensity regions that enhance interaction volumes. Lower-order MPA processes demonstrate greater overall absorption efficiency, with two-photon absorption showing the most dramatic transmittance reductions, while higher-order processes exhibit progressively weaker absorption despite their enhanced intensity sensitivity. Remarkably, while minimum transmittance varies significantly with beam profile, the Full Width at Half Maximum increases linearly with super-Gaussian parameters, revealing fundamental scaling relationships governing nonlinear interaction spatial extent. These findings establish important design principles for optical limiting systems, precision laser manufacturing, medical applications, and material characterization techniques, providing a comprehensive framework for optimizing nonlinear optical interactions through strategic beam profile selection and offering valuable insights for both fundamental research and practical applications in modern photonics.

In this study, we investigate the light propagation characteristics within an integrating cavity, focusing on the transition from a non-uniform light field (NULF) to a uniform light field (ULF). We challenge the conventional assumption in integrating cavity theory that postulates the immediate establishment of a ULF upon light entry. Employing both experimental and simulation approaches, we derive the time constant of the integrating cavity under ULF conditions and measure the cavity’s transient and steady-state responses. Our findings reveal that while a brief NULF phase precedes the ULF, the total radiant flux within the cavity adheres to the ULF propagation law from the onset. This study demonstrates that the NULF can be treated as an approximation of the ULF in terms of total radiant flux variation within an integrating cavity. Our study not only provides empirical validation for integrating cavity theories based on the ULF assumption but also presents compelling evidence of their efficacy in cavities with diverse geometries.

In lateral shearing interferometry, the discretely distributed edges and weak gradient variations in shearing interferograms can adversely affect the accurate calculation of shear parameters, consequently degrading wavefront reconstruction precision. To address this issue, this study proposes a TransUNet-based transfer learning method for shear parameter calculation. First the model pre-trained with simulated interferograms to learn fringe characteristics, then the model fine-tunes with limited real experimental data to overcome the scarcity of real interferograms. The model can achieve precise four-class segmentation of interferograms (background, two non-interference regions, and interference fringes), building upon the segmentation results, least-squares circle fitting algorithm is applied to simultaneously accomplish shear parameter calculation and wavefront center localization. Experimental validation demonstrates that the proposed method maintains excellent computational precision and automation levels even under noisy and weak-gradient conditions, while the shear parameters calculated by our method achieve significantly higher accuracy in wavefront reconstruction than existing mainstream algorithms.

We present an experimental scheme for the measurement of the cross–correlation function in optical beams. Our approach involves illuminating a Spatial Light Modulator by an extended thermal source (generation) and a Sagnac–based wavefront folding interferometer (characterization). We emphasize the use of a common–path interferometer due to its easy assembly and high stability features, factors that make this apparatus relevant for practical applications. As illustrative examples, we explore Laguerre–Gauss and Hermite–Gauss modes, highlighting that in the partially coherent regime, their intensity distributions are blurred while retaining essential information in their cross-correlation function.

This work presents a comprehensive variational and numerical analysis of hyperbolic-function optical beams—hyperbolic tangent-Gaussian (ThG), sine-Gaussian (ShG), and cosine-Gaussian (ChG) profiles—in strongly nonlocal nonlinear media. The novelty lies in deriving exact dynamical solutions and stability criteria for each profile, enabling direct comparison of confinement efficiency, critical power, and robustness. Quantitative results show that ChG beams achieve the lowest critical power for self-trapping, with (P_{textrm{cr}}^{textrm{ChG}}) up to (37%) lower than ShG and (22%) lower than ThG at (m=3), and maintain stable propagation up to 2.1 times their critical power threshold. ChG profiles also exhibit the broadest stability domain in the ((m, P_0)) parameter space and the highest confinement efficiency, with efficiency values exceeding those of ThG and ShG by factors of 1.5 and 2.3, respectively, for (sigma =5). Spectral analysis reveals that increasing the profile order m leads to a 1.8 times broadening of the spectral energy for ChG beams compared to ThG. These findings establish ChG beams as optimal for robust, power-efficient self-trapped beam propagation in nonlocal nonlinear optical systems and provide universal design principles for advanced soliton-based photonic devices. The findings offer direct applicability in advanced soliton-based photonic devices including all-optical soliton routers, reconfigurable beam steering platforms in nematic liquid crystals, and hollow Gaussian pulse control in photonic crystal fibers. The ability to engineer beam symmetry and stability under nonlocality provides a foundation for robust nonlinear signal processing.

A piecewise hollow-core fiber (HCF) consists of two or more segments of HCFs that are in tandem, which can extend the functions of currently widely-used gas-filled HCF compressors. In this work, we present a model to study the influence of misalignment on the pulse propagation dynamics, which includes incident angle deviation and transverse shift between two consecutive segments. In particular, we focus on soliton dynamics involving dispersive wave (DW) emission in vacuum ultraviolet range and sub-cycle pulse generation. It is found that DW emission is more sensitive to incident angle deviation due to shorter wavelengths, and an empirical estimation of the incident angle tolerance is obtained. The tolerance of transverse shift is up to 20 μm in the case studies, which can be met in practice. This work provides insights into the working of a piecewise HCF system that can help to build and analyze such systems.

The design features MXene–SiO₂–Fe-based metasurfaces to enhance efficient absorption across a wide range of the solar spectrum. The proposed investigation of the absorber is essential for an efficient thermal energy harvesting solution and a broad frequency range of both infrared and visible light absorber architectures. The findings derived from computational and numerical analyses will assist in identifying optimal material geometries for effective wideband infrared and visible UV light absorbers and thermal harvesting structures. The entire structure is evaluated against interference theory-based calculations to ascertain effective absorption across the solar spectrum. The basic parameters, such as refractive index, permittivity, permeability, and impedance, were presented for the proposed structure to identify its metamaterial effect. This study introduced a double-multilayer structure of SiO₂ and Fe as the metamaterials. MXene is a resonator in the THz frequency range at an angle of incidence of 60° degrees, within the range of plasmonic insensitivity. The absorption capacity reaches > 90%, making the proposed structures suitable for harvesting solar energy. In addition, the simulated results show high thermal radiation and high thermal efficiency with increasing temperature, emphasizing the importance of simulating MXene as a resonator. The proposed structure can be crucial for designing highly efficient parasitic solar absorbers for multiple solar and thermal absorption applications.

This study systematically investigates the beam quality degradation in conventional broad-area semiconductor lasers, which arises from the excitation of higher-order transverse modes under high injection currents. To address this fundamental limitation, we propose and demonstrate a novel lateral surface grating structure integrated on both sides of the ridge waveguide. Through comprehensive numerical and experimental analyses, we first examine the optical loss characteristics induced by the grating structure. Subsequently, we explore the mode modulation mechanism by systematically varying the separation distance between the gratings and the ridge waveguide. Our results reveal that reducing this critical distance significantly enhances the grating's ability to suppress higher-order transverse modes. This improvement manifests in two key aspects: (1) a notable reduction in the transverse divergence angle in the far-field pattern, and (2) a more concentrated energy distribution in the near-field profile. These findings demonstrate the effectiveness of our proposed approach in achieving superior beam quality while maintaining stable laser operation.