物理与天体物理最新文献

The impact of partially coherent Gaussian beams using Exponential-Weibull (EW) turbulence channels is examined within a single-input single-output (SISO) underwater wireless optical communication (UWOC) system. The importance of the beam is demonstrated by the fiber coupling efficiency. The main causes of interruption of the optical beam are attenuation and turbulence, measured by scintillation index (SI). In addition, closed-form expressions for average bit error rate (BER) utilizing various modulation techniques and outage probability (OP) are derived using the heterodyne detection (HD) technique. Performance metrics are improved by various parameters like temperature and salinity contributions, turbulent kinetic energy, distance, degree of partial coherence, and average SNR.

Circular Airy (CAi) beams, also known as abrupt autofocusing (AAF) beams, represent a distinct class of structured optical fields whose propagation is governed by inward-accelerating wavefronts and caustic-driven energy localization. While their unique focusing dynamics and high-intensity focal spots have been extensively studied, their role as illumination fields for image formation has remained largely unexplored. Here, we present the first systematic investigation, to our knowledge, of image formation using AAF illumination, establishing a direct connection between the focal-spot physics of AAF beams and their imaging performance. We show that the autofocusing mechanism of AAF beams produces a compact, Bessel-like focal core with reduced transverse extent and extended axial persistence compared to Gaussian illumination, enabling improved resolution and depth of focus in imaging. Through a unified Fourier-optics framework, we demonstrate that the structured AAF point spread function preserves spatial-frequency support over defocus, allowing direct image formation with enhanced robustness. These results position AAF beams as a physically grounded illumination strategy for high-resolution, extended-depth imaging and establish structured autofocusing fields as a new degree of freedom in optical image formation.

Placido-ring corneal topography is essential for refractive surgery planning, keratoconus screening, and postoperative monitoring, but reconstructing corneal shape is difficult because it is a nonlinear specular-reflection inverse problem and is vulnerable to noise, tear-film breakup, and missing reflections. We propose physics-guided neural reconstruction (PGNR), a convolutional framework that reconstructs corneal elevation from polar Placido measurements while enforcing meridional geometric-optics forward-model consistency through a measurement-space loss that reduces nonlinear noise bias. Under controlled degradation, PGNR reduces the elevation mean absolute error (MAE) by 69% versus forward ray-tracing, while its elevation MAE increases by only 5.1% with 20% missing data.

Single-ended vibration localization based on frequency-shifted optical delay lines avoids the time synchronization required by dual-ended schemes but requires costly narrow-linewidth lasers. To overcome this limitation, we introduce a transmitter-side matched-delay local oscillator (MD-LO) for the sensing unit. The MD-LO matches the sensing-link length and the delay paths between frequency-shifted components, which can tolerate laser phase noise through self-coherent detection. With sensing aided by the MD-LO, vibration detection down to 10 Hz under a 3-MHz-linewidth distributed-feedback (DFB) laser is achieved, and single-ended distributed vibration localization over a 25.2-km weakly coupled four-core fiber is demonstrated. As an illustrative example of integrated sensing and communication (ISAC), the sensing carrier also serves as the local oscillator for self-coherent communication, achieving 3 × 448 Gb/s net transmission over the remaining three cores.

We demonstrate a Kerr-lens mode-locked (KLM) room-temperature Ti:sapphire laser achieving an average power exceeding 10 W in a single transverse mode with a slope efficiency of 35%. The laser operates at a repetition rate of 73.8 MHz, delivering sub-100-fs pulses with a maximum single-pulse energy of 160 nJ. Owing to excellent thermal management, the laser maintains long-term operation with a root-mean-square (RMS) power fluctuation of 1.08% at a power of 10.3 W over 6 hours. To the best of our knowledge, this represents the highest average power ever reported from a femtosecond Ti:sapphire mode-locked oscillator.

We investigate topological synchronization in electrically driven semiconductor nanolaser arrays. By embedding a non-Hermitian topological Hamiltonian into complex-amplitude-carrier rate equations, we construct a nonlinear array model including carrier dynamics, linewidth enhancement, deterministic spontaneous emission, photon lifetime, and gain saturation. Numerical simulations show that when the coupling Hamiltonian is in a topological phase, edge nanolasers can form highly coherent frequency synchronization, whereas interior nanolasers do not participate in the same global locking process. A comparison with a trivial phase verifies that this selective edge synchronization originates from topological boundary modes rather than ordinary coupling-induced locking. Variations of parameters further show that the phenomenon is robust against changes in the Purcell factor and spontaneous-emission coupling factor but requires a finite window of pump strength and coupling strength. These results connect non-Hermitian topological photonics with realistic nanolaser-array dynamics and provide a theoretical route toward dense coherent nanolaser sources.

Polarization-resolved high-order harmonic generation from oriented polar molecules encodes electron recollision from opposite molecular directions, yet the underlying interference is hidden in intensity spectra. Here we decompose the polarization-resolved harmonic response of carbon monoxide molecules into four ionization-recombination amplitudes associated with the carbon and oxygen centers. The calculated spectra reproduce the established odd-even polarization pattern and reveal distinct orientation-dependent behavior for neighboring harmonics near the cutoff. Molecular rotation converts destructive interference into phase locking of the carbon-ionization amplitudes for the even harmonic, whereas increasing phase competition suppresses the neighboring odd harmonic. This contrast is manifested in the orientation-dependent polarized yields, the polarization imbalance, and the contrasting activation and suppression of neighboring harmonics, providing experimentally accessible signatures of microscopic interference in oriented polar molecules.

We demonstrate self-injection locking (SIL)-based bright and dark-pulse microcomb generation in an ultrahigh-Q crystalline magnesium fluoride (MgF₂) microresonator in the telecom C-band. By simple tuning of the laser injection current, both a single bright soliton and a dark-pulse state are obtained in the same resonator. We further perform a direct comparison of SIL-induced linewidth reduction using the same laser chip with a 10-GHz-FSR MgF₂ resonator and a 100-GHz-FSR silicon nitride microring resonator. The MgF₂ resonator exhibits substantially stronger noise suppression, reaching a hertz-level Lorentzian linewidth of 1.78 Hz. These results highlight ultrahigh-Q crystalline resonators as a promising platform for ultralow-noise microwave-rate coherent comb generation.

In this paper, the propagation characteristics of the dual-ring perfect vortex beam (DR-PVB) with full manipulation of its amplitude, radius, beam width, and topological charge (TC) for each ring in a gradient-index (GRIN) medium are systematically investigated. The influences of TCs l_o and l_i, ring radii w_o and w_i, full widths at half-maximum (FWHM) d_o and d_i, and the factor of GRIN medium b on beam evolution, especially on the focal field pattern, are analyzed. DR-PVB experiences periodic focusing and produces multilayered focal structures. By tuning beam and medium parameters, the number of bright spots and the peak intensity at the focal plane, and the focusing period can be flexibly controlled, respectively. l_o and l_i jointly regulate field intensity distributions and rotation directions. Proper ring radii and FWHM raise focal peak intensity. Reducing b shortens the focusing period and strengthens focal light intensity. Moreover, radiation force calculations demonstrate that DR-PVBs enable multi-position particle trapping and improved trapping stiffness via multimodal transverse and smooth axial optical forces. This work provides a feasible strategy for flexibly engineering vortex light fields in GRIN media and promotes their applications in optical manipulation.

Scattering of Ince-Gaussian (IG) beams by a homogeneous dielectric sphere is investigated using a volume integral equation formulation solved numerically using the method of moments. The incident IG beams are characterized by their mode indices, parity, beam waist, semi-focal distance, and polarization state. The scattering characteristics are analyzed in terms of directivity, normalized total scattered power, and normalized absorbed power. Validation of the formulation is established through comparisons with limiting cases, including plane-wave and Laguerre-Gaussian-beam incidences. Numerical results reveal that the directivity patterns strongly depend on the beam mode indices, namely the order and degree, as well as the beam parity. Odd-order modes exhibit zero directivity in the forward and backward directions, consistent with a symmetry property of the incident field. The dependence of the directivity on the semi-focal distance is shown to be linked directly to the sensitivity of the corresponding Ince polynomials. Furthermore, the effect of the beam waist on the directivity depends on the mode, with changes in the maximum directivity and the depths and positions of the minima. The normalized total scattered and absorbed powers increase with the electrical size of the sphere, while their magnitudes depend strongly on the beam mode, with considerably lower values observed for some higher-order modes. However, the modes with the highest normalized total scattered power do not necessarily have the highest normalized absorbed power. The influence of polarization is found to be weak for the fundamental mode and IG_2,0 ^e , but more pronounced for some other modes, with absorption generally showing a stronger dependence on the polarization state than scattering.