Applied Physics B最新文献

This paper investigates the nonlinear propagation dynamics of finite Airy-Gaussian (AiG) laser beams in a uniform dense collisionless plasma using the Wentzel-Kramers-Brillouin (WKB) and paraxial ray approximations. Instead of treating the coupled beam width parameter differential equations (BWPDEs) solely as evolution equations, the beam propagation is analysed within an equivalent classical dynamical framework. The beam width evolution is reformulated as a two-dimensional dynamical system governed by propagational quasi-Hamiltonian functional and an effective pseudo-potential. An energy-like propagational quasi-Hamiltonian functional is derived characterizes the nonlinear beam dynamics. The evolution of the system is further interpreted through kinetic energy-like and effective pseudo-potential terms. The analysis reveals that, the quasi-Hamiltonian functional governs the self-trapping, oscillatory self-focusing and defocusing behavior of the beam. Different propagation regimes are identified according to the evolution of the quasi-Hamiltonian functional; near-zero values correspond to self-trapping, bounded oscillations indicate stable propagation and divergent behaviour signifies beam defocusing. The condition for self-trapping, self-focusing, defocusing and beam stability are further examined through a Hessian matrix analysis. The proposed framework provides deeper physical insights into the nonlinear dynamics of finite AiG beams and extends the conventional beam width parameter approach by revealing the underlying dynamical structure of beam propagation in plasma.

With the exponential growth of digital communication channels, the transmission and storage of high-dimensional multimedia data, including images and videos, have become crucial to modern information systems. The areas like defense, healthcare and banking utilize the modern communication channels very often to share information. Thus, ensuring the confidentiality, integrity, and authenticity of sensitive visual information has become a critical challenge. Although there are various conventional data security algorithms that exist, they often encounter limitations in handling large-scale image data due to high computational complexity and slow processing speed. Optical cryptosystems have emerged as a promising alternative owing to their inherent parallelism, multidimensional processing capability, large key space, and high-speed implementation. In this review, recent advancements in optical cryptosystems beyond classical DRPE scheme are summarized. Particularly, we examine the asymmetric optical cryptosystems based on PTFT, QZ decomposition, QZ synthesis, SVD, GSVD, interference, and computer-generated holography. Moreover, this review also discussed the emerging approaches of optical data security using structured light beams such as vector vortex beams. Finally, the review covered various techniques to test the vulnerabilities of optical cryptosystems such as plaintext and modified plaintext attacks, AI based cryptographic attacks, and iterative attacks designed for asymmetric cryptosystems. The objective of this review article is to serve as a reference text for readers from a variety of research backgrounds interested in the domain of optical information security.

Atomic vapor laser isotope separation (AVLIS) of gadolinium has historically emphasized enrichment of the odd isotopes, with external magnetic fields treated primarily as a source of selectivity degradation. Here we revisit polarization-selective photoionization of gadolinium with a different objective: to exploit controlled B-field–induced mixing as a design parameter for enhancing the photoionization of even isotopes. Using density-matrix simulations of a J = 2 → 2 → 1 → 0 excitation ladder, we examine the combined effects of magnetic-field orientation and amplitude, laser polarization, and laser fluence on the photoionization efficiency of ¹⁶⁰Gd and ¹⁵²Gd. We identify operating regimes in which modest magnetic fields (≈10–20 G), appropriately oriented relative to the laser fields, substantially increase even-isotope photoionization probability without catastrophic loss of selectivity. When translated into separation metrics, these conditions yield high theoretical product assays and isotopic cuts approaching or exceeding 60–70% in a single pass, representing approximately a two-fold improvement in isotopic cut relative to zero-field operation. The results demonstrate that magnetic fields need not be treated solely as a limitation in polarization-selective AVLIS but can instead be leveraged to improve throughput for even-isotope enrichment, particularly for rare isotopes such as ¹⁵²Gd, and suggest that AVLIS can be competitive with electromagnetic isotope separation for the production of even gadolinium isotopes.

Water-jet guided laser (WJGL) processing provides an effective technology for the precision machining of ceramic matrix composites (CMCs), particularly for high-aspect-ratio microhole drilling, owing to its advantages in energy confinement, cooling, and debris removal. In this study, WJGL processing and dry nanosecond laser processing were systematically compared for the drilling of C_f/SiC composites under comparable laser conditions. The results show that the introduction of water significantly modifies the laser-material interaction by providing cooling and debris removal, thereby reducing thermal accumulation and subsequent oxidation. By optimization of water pressure, microholes with a minimum diameter of 200 μm and a maximum aspect ratio of 15:1 were successfully fabricated. Compared with dry nanosecond laser processing, WJGL achieved a higher material removal rate while markedly suppressing thermal oxidation at the cross section, thus preserving the integrity of both the SiC matrix and the BN interface. Consequently, the WJGL-processed C_f/SiC composites show significantly improved wear resistance compared to the dry nanosecond laser-processed ones due to the reduced surface damage.

Digital holographic microscopy (DHM) involves computationally demanding operations such as numerical wave propagation, phase retrieval, and three-dimensional (3D) reconstruction, which rely heavily on large-scale matrix computations. As spatial resolution and sampling density increase, the associated computational burden grows substantially, often necessitating optimized signal-processing strategies to enable real-time and high-fidelity reconstruction. To address this, we propose a sparse reconstruction method based on adaptive dictionary learning (DL) named as Sequential Generalized K-means (SGK) is integrated into DHM. In the proposed method, input hologram is divided into patches, and each patch is represented as linear combination of sparse dictionary atoms. Each atom in dictionary is updated sequentially by averaging the training patches associated with its fixed sparse coefficients. Unlike K-SVD, proposed method avoids the expensive singular value decomposition (SVD) for dictionary update thereby minimizes the computation time and improves the hologram reconstruction accuracy. To further enhance reconstruction quality, optimum choice of key parameters such as patch size, dictionary size, and sparsity level is essential. Experimental results demonstrate that the proposed SGK-based sparse reconstruction achieves high-fidelity reconstructions and faster convergence than conventional dictionary-learning approaches, highlighting its suitability for real-time microscopic imaging applications.

Light fields with a central wavelength of 2 µm are very well suited for strong-field-driven charge carrier control: Their photon energy lies far below the band gap of many materials, while their oscillation period remains significantly shorter than the coherence time of charge carrier oscillations. The resulting potential for field-driven charge carrier control is contingent on the reproducibility of the field structure of such ultrashort laser pulses. Here, we present a compact 200-kHz laser system that delivers ultrashort pulses with a duration of less than 20 fs in the spectral range around 2 µm and with a pulse energy of 25 µJ. The electric field structure of the 2-µm pulses is characterized in detail. In particular, the carrier-envelope phase (CEP) is measured over a wide range of timescales, from microseconds to hours. Passive stabilization due to difference frequency generation results in a root mean square value of carrier-envelope phase noise of less than 70 mrad over all measured time scales. The applicability of the pulses is demonstrated by measuring CEP-dependent high-order harmonic spectra with energies of up to 160 eV.

This paper presents a physics-guided stepwise tomography framework that decouples the ill-posed tomography of temperature and concentration into three measurement- and prior-guided stages. By sequentially embedding two-line thermometry, projection matrix, and structural similarity, the framework first reconstructs a preliminary temperature field via a physics-data collaborative network, then employs it as a structural prior to guide iterative concentration inversion, and finally restores spatial details through a joint superresolution network, achieving high-fidelity reconstruction under a sparse optical layout with 40 optical paths and 2 absorption lines. Comprehensive validation in three cases supports improved robustness in the tested cases. In Case A, an in-distribution LES test dataset achieved dataset-averaged temperature/concentration mean relative errors ((E_T/E_X)) of 1.35%/2.51% and temperature/concentration structural similarity indices ((SSIM_T/SSIM_X)) of 0.991/0.989. In Case B, an out-of-distribution LES flame with modified inlet conditions showed section-dependent performance, with representative noise-free longitudinal sections giving (E_T=4.54%-7.67%), (E_X=5.55%-14.11%), (SSIM_T=0.742-0.974), and (SSIM_X=0.763-0.965). In Case C, an experimentally derived axisymmetric flame case constructed from Sandia Flame D measurements further showed that the main jet, reaction-zone, and diffusion-region structures can still be captured; representative cross-sections achieved (E_T<5%), (E_X<8%), (SSIM_T>0.98), and (SSIM_X>0.96). This strategy provides a promising route toward real-time combustion diagnostics in geometrically complex environments with restricted optical access.

Spatially resolved, quantitative laser diagnostics are needed to understand high-temperature and high-speed flow fields. To that end, a spectrally resolved laser-induced fluorescence diagnostic targeting nitric oxide (in bath gases of Ar and N₂) was developed and validated in a series of static cell and shock tube experiments. Also, a spectrally resolved fluorescence model was created to simulate the underlying processes of diatomic spectrally resolved fluorescence and quantify the maximum theoretical measurement rate under various conditions. The diagnostic was validated from 295–1350 K and 2.1–47.0 kPa, and validation experiments showed good agreement with known values—a 3.0% and 5.5% average error in temperature and pressure (for collisional-to-Doppler width ratios greater than 0.30), respectively.