分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: We propose a novel coaxial spherical-lens shaping system to achieve a flat-top focus profile by exploiting the spherical aberration of the lens. The well-known aspherical-lens shaping system is compared to ours, and a comparison of etching on silicon is conducted between a Gaussian beam and the one shaped by the proposed system. Analytical and experimental results show that the proposed system is able to achieve flat-top beam shaping using only spherical lenses. Compared with the existing systems, our proposed one is capable of shaping Gaussian beams with different wavelengths and waist radii. Furthermore, the shaped one obtained by ours is the flat-top beam with extended depth of focus. This letter provides an efficient and precise flat-top beam shaping scheme for optics and laser technology, and increases the potential of spherical lenses in the field of laser shaping.
分类: 物理学 >> 核物理学 提交时间: 2023-07-12
摘要: The in-medium feature of nuclear force which includes both nucleon-nucleon ($NN$) and hyperon-nucleon ($\Lambda N$) interactions impacts the description of single-$\Lambda$ hypernuclei. With the alternated mass number or isospin of hypernuclei, such effects could be unveiled by analyzing systematical evolution of the bulk and single-particle properties. From a density-dependent meson-nucleon/hyperon coupling perspective, a new $\Lambda N$ effective interaction in the covariant density functional (CDF) theory, namely DD-LZ1-$\Lambda1$, is obtained by fitting the experimental data of $\Lambda$ separation energies for several single-$\Lambda$ hypernuclei. It is then adopted to study the structure and transition properties of single-$\Lambda$ hypernuclei in Oxygen isotopes, comparing with several selected CDF Lagrangians. Discrepancy is observed explicitly in the isospin evolution of $\Lambda1p$ spin-orbit splitting with various effective interactions, ascribed to their divergence of the meson-hyperon coupling strengths with increasing density. In particular, the density-dependent CDFs introduce an extra contribution to enhance the isospin dependence of the splitting, which is originated from the rearrangement terms of $\Lambda$ self-energies. In addition, the characteristics of hypernuclear radii are studied along the isotopic chain. Owing to the impurity effect of $\Lambda$ hyperon, a size shrinkage is observed in the matter radii of hypernuclei as compared to their cores of normal nuclei, while its magnitude is elucidated further to correlate with the incompressibility of nuclear matter. Besides, there exists a sizable model-dependent trend that $\Lambda$ hyperon radii evolve with the neutron number, which is decided partly by the in-medium $NN$ interactions as well as the core polarization effects.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: In recent years, the optical 4f system has drawn much attention in building high-speed and ultra-low-power optical neural networks (ONNs). Most optical systems suffer from the misalignment of the optical devices during installment. The performance of ONN based on the optical 4f system (4f-ONN) is considered sensitive to the misalignment in the optical path introduced. In order to comprehensively investigate the influence caused by the misalignment, we proposed a method for estimating the performance of a 4f-ONN in response to various misalignment in the context of the image classification task.The misalignment in numerical simulation is estimated by manipulating the optical intensity distributions in the fourth focus plane in the 4f system. Followed by a series of physical experiments to validate the simulation results. Using our method to test the impact of misalignment of 4f system on the classification accuracy of two popular image classification datasets, MNIST and Quickdraw16. On both datasets, we found that the performances of 4f-ONN generally degraded dramatically as the positioning error increased. Different positioning error tolerance in the misalignment orientations was observed over the two datasets. Classification performance could be preserved by positioning errors up to 200 microns in a specific direction.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: When imaging moving objects, single-pixel imaging produces motion blur. This paper proposes a new single-pixel imaging method, which can achieve anti-motion blur imaging of a fast-moving object. The geometric moment patterns and Hadamard patterns are used to alternately encode the position information and the image information of the object with time-division multiplexing. In the reconstruction process, the object position information is extracted independently and combining motion-compensation reconstruction algorithm to decouple the object motion from image information. As a result, the anti-motion blur image and the high frame rate object positions are obtained. Experimental results show that for a moving object with an angular velocity of up to 0.5rad/s relative to the imaging system, the proposed method achieves a localization frequency of 5.55kHz, and gradually reconstructs a clear image of the fast-moving object with a pseudo resolution of 512x512. The method has application prospects in single-pixel imaging of the fast-moving object.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We investigate the reach of the LIGO/Virgo/KAGRA detectors in the search for signatures of first-order phase transitions in the early Universe. Utilising data from the first three observing runs, we derive constraints on the parameters of the underlying gravitational-wave background, focusing on transitions characterised by strong supercooling. As an application of our analysis, we determine bounds on the parameter space of two representative particle physics models. We also comment on the expected reach of third-generation detectors in probing supercooled phase transitions.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The Tianlai Dish Pathfinder array is a radio interferometer array consisting of 16 six meter dish antennas. The original digital backend integration time is at the seconds level, designed for HI intensity mapping experiment. A new digital backend with millisecond response is added to enable it to search for fast radio burst (FRB) during its observations. The design and calibration of this backend, and the real time search pipeline for it are described in this paper. It is capable of forming 16 digital beams for each linear polarisation, covering an area of 19.6 square degrees. The search pipeline is capable of searching for, recording and classifying FRBs automatically in real time. In commissioning, we succeeded in capturing the signal pulses from the pulsars PSR B0329+54 and B2021+51.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Realtime trigger and localization of bursts are the key functions of GECAM, which is an all-sky gamma-ray monitor launched in Dec 10, 2020. We developed a multifunctional trigger and localization software operating on the CPU of the GECAM electronic box (EBOX). This onboard software has the following features: high trigger efficiency for real celestial bursts with a suppression of false triggers caused by charged particle bursts and background fluctuation, dedicated localization algorithm optimized for short and long bursts respetively, short time latency of the trigger information which is downlinked throught the BeiDou satellite navigation System (BDS). This paper presents the detailed design and deveopment of this trigger and localization software system of GECAM, including the main functions, general design, workflow and algorithms, as well as the verification and demonstration of this software, including the on-ground trigger tests with simulated gamma-ray bursts made by a dedicated X-ray tube and the in-flight performance to real gamma-ray bursts and magnetar bursts.