Applied Physics B最新文献

A dispersion-managed femtosecond optical parametric oscillator (OPO) with stable power is demonstrated in this article. The OPO, based on LiB₃O₅ (LBO) crystal, was synchronously pumped by a frequency-doubled, Kerr-lens mode-locked Yb: CGYA laser. The output signal had a wavelength tuning range of 680 ~ 740 nm, a maximum average power of 1.1 W, and a minimum pulse duration of 105 fs. By inserting ultraviolet fused silica (UVFS) windows into the cavity to introduce additional normal dispersion, the dual-signal-wavelength output was suppressed, and the power stability was significantly enhanced. The RMS of the one-hour power fluctuation decreased to one seventh of its original value, from 2.47% to 0.38%. This work is of particular significance for promoting the engineering application of femtosecond OPOs.

This study presents both numerical modeling and experimental fabrication of three different partial-reflection (PR) coatings each optimized for quantum cascade lasers (QCLs) that emit radiation in the mid-infrared range. A novel double-layer PR coating comprising silicon dioxide (SiO₂₎ and silicon nitride (Si₃N₄) was proposed as a potential solution for compatibility with QCLs fabrication processes. Subsequently, the PR coating was compared with two well-known PR coatings: a single layer of aluminum oxide (Al₂O₃) and a single layer of yttrium oxide (Y₂O₃). The coatings were designed to reduce the reflectivity of the front laser mirror from 30% to approximately 13%. The thickness of the dielectric layers was optimized for lasers emitting at 4.4 μm, with applicability in the 2.5–6 μm range. The proposed double-layer coating achieved the desired reflectivity while reducing the total coating thickness by 120 nm. By using the presented coatings it will be possible to increase the optical power of Mid-Infrared QCLs.

Unlike the deterministic theory of modulation instability (MI), which describes this process in terms of a well-defined gain spectrum and a well-resolved threshold, the statistical treatment of MIs, presented in this study, is concerned with a question as to how probable MI-driven beam-instability events are. We show that stochastic laser beams that nominally meet the deterministic beam-stability criterion can emerge as unstable on large pulse samples. With the laser peak power set well below the deterministic MI threshold, the count rate of MI-driven beam-instability events within a large sample of laser pulses is shown to be Poissonian-distributed, with its mean defined by the exponent of the extreme-event beam-instability statistics. We present a closed-form analytical solution for this beam-instability count rate, revealing the key tendencies in its behavior as a function of the signal-to-noise ratio and the bandwidth of its noise component. We demonstrate that the stochastic beam-instability dynamics of high-power laser field waveforms, including the laser pulses used for the ignition of inertial confinement fusion, can be scaled down in laser power and studied in laboratory-scale laser experiments.

This article describes the measurement procedure and data processing features of an apparatus for measuring the spectral emissivity of electrically conductive opaque materials in air. The developed laboratory setup has the following three main features: induction heating of the sample, correction in order to exclude the surrounding radiation reflected by the sample, and the use of multiwavelength pyrometry. Single-sided induction heating of the sample eliminates the contribution of stray radiation from the heating element to the recorded signal. The correction on surrounding radiation increases the accuracy of emissivity determination, especially at low temperatures. The multiwavelength pyrometry is used to obtain the true temperature of a sample. This technique makes it possible to obtain the surface temperature of the sample directly from its thermal radiation spectrum, allowing to examine the material during the oxidation process. The emissivity spectra of zirconium and hafnium diboride samples were measured with the created setup. The obtained spectra reveal several features, which correlate with chemical transformations on the surface of the materials during oxidation.

A novel approach is proposed for accelerating Rydberg atoms utilizing two-dimensional Pearcey beams instead of traditional circular symmetric beams such as Gaussian beams. The structure of the two-dimensional Pearcey optical field can achieve quasi-unidirectional acceleration of atoms within a small spot size, which is conducive to improving the detection efficiency. In addition, the self-focusing characteristic of this beam can significantly reduce the required intensity of the driving source compared to the traditional scheme using the Gaussian beams.

Using Dammann grating (DG) metasurfaces enables miniaturization and integration of devices for generating structured light, allowing them to be used in different applications with different types or working wavelengths of structured light. However, most existing DG metasurfaces are based on Hermitian photon systems, and there has been no exploration of the results of DG metasurfaces under non-Hermitian photon system conditions. In this study, we numerically constructed a non-Hermitian DG metasurface with parity-time (PT) symmetry of the adjacent silicon dioxide substrate and lithium niobate (LiNbO3, LN) nanorods. Simulation results have demonstrated that introducing PT symmetry into DG metasurfaces alters their response wavelengths, leading to changes in the structured light patterns. To further investigate the effects introduced by incorporating PT symmetry into diffraction gratings, we have also designed two types of pseudo-Dammann gratings (PDG), namely, annular PDG and cross-shaped PDG. Incorporating PT symmetry into PDG not only improved the uniformity of the diffracted light spot arrays but also altered the distribution arrangement of the spots in one type of PDG, enabling the generation of novel and unique structured light patterns in the far field. This study theoretically proposed a PT-symmetric and dynamically tunable metasurface structure, providing a new approach for the design, control, and fabrication of dynamically adjustable optical components.

In recent years, space–time-modulated metasurfaces have garnered significant attention. Programmable space–time-coding digital metasurfaces have emerged as powerful platforms for realizing space–time modulation and have been successfully employed for manipulating electromagnetic waves in both spectral and spatial domains. This article systematically introduces the general concepts and working principles of space–time-coding digital metasurfaces. It provides an overview of the latest advancements in wireless communication within this field and summarizes the challenges and future directions in this rapidly evolving research area.

Changes in environmental conditions will directly influence the intensity of turbulent motion, and a random variation of the refractive index ensues. In this paper, a phase-based moiré deflection tomography is used to explore the effect of thermal disturbance on the spatial and temporal distributions of the refractive index structure constant, which is achieved after passing parallel beams through the indoor convective air turbulence. Initially, experiments are conducted for 60 min under two conditions: with and without the thermal flow field. In each set, 3600 frames of moiré fringes are successfully captured. And then, the temporal and spatial distributions of the refractive index structure constant are obtained. Subsequently, its regularities of distribution are analyzed in combination with the reconstructed temperature of the thermal flow field. Finally, the finding reveals a strong positive correlation between the refractive index structure constant and temperature fluctuations, in particular, the pronounced influence of thermal disturbance leads to a rapid exponential rise in its values. In a word, the related results could provide valuable insights for studying atmospheric optical communication and laser detection.

In this paper, we perform a cryptanalysis of a previously published symmetric cryptosystem that utilizes the Arnold transform (AT), singular value decomposition (SVD), and the fractional Hartley transform (FrHT) domain. By performing an attack-analysis, it is shown that the symmetric cryptosystem is vulnerable to a Known-Plaintext Attack (KPA). If an attacker knows the cipher-text and the order of the FrHT, attacker can recover the correct combination of SVD and AT parameters used in the image encryption algorithm. To overcome the security weakness of the symmetric cryptosystem, we propose an asymmetric phase image encryption by employing the Arnold transform, Singular value decomposition, and Hessenberg decomposition (HD) in the FrHT domain. The scheme is validated using evaluation metrics; mean-square-error, peak signal-to-noise, entropy, 3D mesh-, correlation-, noise-attack-, occlusion-attack-, and linear-attack analyses. Keys generated by SVD and HD make the cryptosystem asymmetric, making it resistant to Known-Plaintext Attack (KPA) and Chosen-Plaintext Attack (CPA).

We introduce a new utilization of an Aerodynamic Lens Stack (ALS) for concentrating aerosols in the production of high energy (>200 keV) electrons through their interaction with intense((>10^{16}) W/cm(^2)), ultra-short (30 fs) laser pulses. The lens was designed and simulated in COMSOL with various parameters such as inlet dimensions and backing pressures. Subsequently, the particle jet was analyzed using particle streak velocimetry (PSV). Following the characterization process, the jet was exposed to the laser, and the emission of electrons was investigated and described. Our results demonstrate the effectiveness of the lens in producing and focussing aerosols originating from liquid sources, underscoring its potential as a precise microtarget for laser interactions.