Performance optimization of a SERF atomic magnetometer based on flat-top light beam

We explore the impact of pumping beams with different transverse intensity profiles on the performance of the spinexchange relaxation-free(SERF) atomic magnetometers(AMs). We conduct experiments comparing the traditional Gaussian optically-pumped AM with that utilizing the flat-top optically-pumped(FTOP) method. Our findings reveal that the FTOP-based approach outperforms the conventional method, exhibiting a larger response, a narrower magnetic resonance linewidth, and a superior low-frequency noise performance. Specifically, the use of FTOP method leads to a 16% enhancement in average sensitivity within 1 Hz–30 Hz frequency range. Our research emphasizes the significance of achieving transverse polarization uniformity in AMs, providing insights for future optimization efforts and sensitivity improvements in miniaturized magnetometers.

Zone plate design for generating annular-focused beams

Annular-focused beams have attracted attention because of their novel properties and applications in optical trapping, high resolution microscopy, and laser-induced periodic surface structuring. Generation of this beam is very important and necessary. In this article, a novel design of zone plate for forming the annular-focused beams is proposed. The design principle is introduced, and the characteristics of zone plate are analyzed by numerical simulation. The result shows that the zone plate can form a monochromatic ring-shaped intensity distribution in the focal plane. And the design method is also generally suitable for designing the other optical elements to generate the annular-focused beams.

Intensity Distribution of the Finite Olver Beams through a Paraxial ABCD Optical System with an Aperture of Basis Annular Aperture

Based on the Collins diffraction formula and by means of the expansion of a hard aperture function into a finite sum of complex Gaussian functions, two analytical approaches of the Finite Olver beams (FOBs) passing through a paraxial ABCD optical system with a circular annular aperture or a rectangular one are developed in this paper. The propagation properties of the FOBs through an unapertured ABCD optical system or through this last with a circular (or rectangular) aperture or a circular (or rectangular) black screen are deduced, from the main results, as particular cases. Also, the characteristics of Finite ordinary Airy beam passing through the all considered optical systems are derived here that correspond to zeroth-order of the FOBs. According to the predicted formulas, computer simulation examples are given to deepen the understanding of the characteristics of the FOBs passing through some optical systems of annular aperture basis.

Pulling force of acoustic-vortex beams on centered elastic spheres based on the annular transducer model

To solve the difficulty of generating an ideal Bessel beam,an simplified annular transducer model is proposed to study the axial acoustic radiation force(ARF)and the corresponding negative ARF(pulling force)exerted on centered elastic spheres for acoustic-vortex(AV)beams of arbitrary orders.Based on the theory of acoustic scattering,the axial distributions of the velocity potential and the ARF for AV beams of different orders generated by the annular transducers with different physical sizes are simulated.It is proved that the pulling force can be generated by AV beams of arbitrary orders with multiple axial regions.The pulling force is more likely to exert on the sphere with a smaller k0a(product of the wave number and the radius)for the AV beam with a bigger topological charge due to the strengthened off-axis acoustic scattering.The pulling force decreases with the increase of the axial distance for the sphere with a bigger k0a.More pulling force areas with wider axial regions can be formed by AV beams using a bigger-sized annular transducer.The theoretical results demonstrate the feasibility of generating the pulling force along the axes of AV beams using the experimentally applicable circular array of planar transducers,and suggest application potentials for multi-position stable object manipulations in biomedical engineering.

Optimal Design of Aperture Illuminations for Microwave Power Transmission with Annular Collection Areas

This work presents an optimal design method of antenna aperture illumination for microwave power transmission with an annular collection area.The objective is to maximize the ratio of the power radiated on the annular collection area to the total transmitted power.By formulating the aperture amplitude distribution through a summation of a special set of series,the optimal design problem can be reduced to finding the maximum ratio of two real quadratic forms.Based on the theory of matrices,the solution to the formulated optimization problem is to determine the largest characteristic value and its associated characteristic vector.To meet security requirements,the peak radiation levels outside the receiving area are considered to be extra constraints.A hybrid grey wolf optimizer and Nelder–Mead simplex method is developed to deal with this constrained optimization problem.In order to demonstrate the effectiveness of the proposed method,numerical experiments on continuous apertures are conducted;then,discrete arrays of isotropic elements are employed to validate the correctness of the optimized results.Finally,patch arrays are adopted to further verify the validity of the proposed method.

Flat-top beam illumination for polarization-sensitive second-harmonic generation microscopy

Wide-field second-harmonic generation (SHG) was used to obtain the second-harmonic signal from the entire image area for rapid imaging, despite the fact that conventional Gaussian beam illumination has low energy utilization efficiency,which makes it easy to overexpose the intensity of the image center area. However, flat-top beam illumination has uniform spatial distribution, thereby improving the photon excitation efficiency in the entire image region and reducing laser damage and thermal effect. By combining flat-top beam illumination and wide-field SHG polarization measurement, we can calculate more myosin fibril symmetrical axis orientations through polarization analysis of 16 images at a fast imaging speed while expanding the field of view. More importantly, the application of a flat-top beam can further improve the capability of polarization measurement in SHG microscopy.

Production of annular flat-topped vortex beams

A model of an annular fiat-topped vortex beam based on multi-Gaussian superimposition is proposed. We experimentally produce this beam with a computer-generated hologram （CGH） displayed on a spatial light modulator （SLM）. The power of the beam is concentrated on a single-ring structure and has an extremely strong radial intensity gradient. This beam facilitates various applications ranging from Sisyphus atom cooling to micro-particle trapping.

Temperature rise induced by an annular focused transducer with a wide aperture angle in multi-layer tissue

In order to improve the operability and accuracy of high-intensity focused ultrasound （HIFU）, an annular focused transducer, whereby a B-ultrasound probe is placed in its center, is used to realize the real time monitoring and control of the treatment. In this paper, the spheroidal beam equation （SBE） was used to calculate the sound lield by an annular focused transducer with a wide aperture angle to first derive the heat deposition and the Pennes equation was used to calculate the temperature field in multi-layer tissue. We studied the effect of different parameters on the temperature of the tissues. The result shows that the focal length has a significant influence on both maximum liver temperature rise and skin temperature rise, and both increase with the increase in the focal length. When the frequency increases, the temperature rise first undergoes a rapid increase before gradually reaching a maximum, and then finally decreasing. The temperature rise increases while the inner radius decreases or the sound pressure increases. By choosing suitable parameters, the proper temperature rise both on the target tissue and skin via an annular tbcused transducer with a wide aperture angle can be obtained.

Designs of Two-Element Optical Refracting System to Achieve Uniform Laser Beam Profile

Various specific laser irradiance distribution outputs are needed in many applications. To fulfill this need, a detailed step-by-step design procedure for split refracting system is proposed for three types of laser beams transformation: 1) Annular-uniform-to-uniform;2) Annular-Gaussian-to-uniform;and 3) Gaussian-to-uniform to obtain the required laser irradiance distributions. Mathematical expressions of the two Plano-aspheric surfaces are derived for each type. The proposed designs take into account few important parameters such as the system length, the surfaces radii of curvature, the annular beam starting cone angle, and the beams power ratio. Further, the proposed designs are much better than the ones, which were previously

Compact and broadband circularly polarized ring antenna with wide beam-width for multiple global navigation satellite systems

A compact and broadband circularly polarized （CP） annular ring antenna with wide beam-width is proposed for multiple global navigation satellite systems （GNSS） in the L1 band. The annular ring is excited by two modified L-probes with quadrature phase difference. It has a 36.3% 10-dB return loss bandwidth and a 13% 3-dB axial ratio bandwidth, because of the orthogonal L-probes with 90° phase difference. The measured peak gain of the antenna is 3.9 dBic. It can detect the satellites at lower elevation as its half power beam-width （HPBW） is 113° in both the x-z and y-z planes, achieving a cross-polarization level of larger than 25 dB. Noticeably, the antenna achieves 89% size reduction compared with the conventional half wavelength patch antennas. It can be used in hand-held navigation devices of multiple GNSS such as COMPASS, Galileo, GPS and GLONASS.

环状光束在非Kolmogorov大气湍流中传输的理论研究

基于广义惠更斯-菲涅耳原理,利用非Kolmogorov谱,推导出环状光束在非Kolmogorov大气湍流中传输的束宽和角扩展的解析表达式.从理论上分析,它们的变化除了与环状光束的光束参数(束腰、波长、阶数和遮拦比)和传输距离有关外,由于湍流的影响,还与湍流的广义指数参数α、内尺度l0和外尺度L0有关,并进行了一定的物理解释.

E型波导振荡器反转永磁引导系统初步设计

开展了E型波导振荡器永磁引导系统的物理与设计研究。对强流相对论电子束在理想方波形反转引导磁场中的传输条件进行了理论分析,给出了相对论条件下轴对称复合场中电子束的傍轴轨迹方程和最小引导磁场的计算公式。根据该理论分析,针对C波段E型波导振荡器高频互作用区的结构特点,设计了反转永磁引导系统,同时给出了漂移管内各个磁场分量的表达式。该系统由轴径向磁化空心永磁体组合产生反转引导磁场,永磁体的总质量约为2.5 kg。采用爆炸发射阴极,展示了强流相对论电子束在该引导磁场中的传输特性。研究结果显示,所设计反转永磁引导系统可引导400 kV、580 A的环形电子束稳定通过半径为6 mm的漂移管,带入器件,得到112.5 MW的4.8 GHz微波输出功率,效率为48.49%,确定了反转永磁引导系统应用于E型波导振荡器的技术可能性。

Digital generation of super-Gaussian perfect vortex beams via wavefront shaping with globally adaptive feedback

High-intensity vortex beams with tunable topological charges and low coherence are highly demanded in applications such as inertial confinement fusion(ICF) and optical communication. However, traditional optical vortices featuring nonuniform intensity distributions are dramatically restricted in application scenarios that require a high-intensity vortex beam owing to their ineffective amplification resulting from the intensity-dependent nonlinear effect. Here, a low-coherence perfect vortex beam(PVB) with a topological charge as high as 140 is realized based on the super-pixel wavefront-shaping technique. More importantly, a globally adaptive feedback algorithm(GAFA) is proposed to efficiently suppress the original intensity fluctuation and achieve a flat-top PVB with dramatically reduced beam speckle contrast. The GAFA-based flat-top PVB generation method can pave the way for high-intensity vortex beam generation,which is crucial for potential applications in ICF, laser processing, optical communication and optical trapping.

环形光束的聚焦性质研究

从理想的环形光束出发 ,理论上分析了环形聚焦光束在焦点附近的光强分布情况 ,以及光束内外径之比对聚焦性质的影响 .然后利用数值模拟的手段 ,研究了带软化因子的环形光束的聚焦性质 ,在整体上给出了环形光束的聚焦性质 .

0.14THz返波管器件

对有限引导磁场环形电子束的色散曲线作了理论推导,并利用该色散关系数值计算了正弦慢波结构的色散曲线。采用KARAT模拟程序对0.14 THz返波管进行了粒子模拟,并在RADAN303脉冲源上开展了初步的实验研究,实验获得频率大于0.14 THz、脉冲宽度1-2 ns和辐射功率大于100 kW的太赫兹波输出。

相对论行波管色散特性分析

数值计算了一种填充等离子体的波纹波导结构的行波管 ,在强引导磁场下 ,被一环形相对论电子注驱动的小信号增益。详细地分析了等离子体的浓度、电子注的电压、电流及其在慢波结构中的传输位置对行波管的增益。

轴棱锥光学系统对激光束的变换及应用

本文对轴棱锥系统对激光束的变换特性作了详细分析。结果表明，本文提出的新型轴棱锥光学系统具有某些实际应用价值。

贝塞尔-高斯光束通过圆孔与圆环光阑的衍射

为了研究贝塞尔-高斯光束通过圆孔硬边光阑和圆环光阑的衍射特性,从Collins公式出发,采用数值模拟的方法模拟出光强分布。模拟结果表明,贝塞尔-高斯光束经圆孔光阑衍射后轴上光强随菲涅耳数F呈周期振荡;贝塞尔-高斯光束经圆环光阑后轴上光强随F呈振动衰减。在F相同时,贝塞尔-高斯光束经圆孔光阑衍射后横向光强分布比经圆环光阑衍射后横向光强分布平滑,孔径越小,光强调制越明显;当孔径与束腰相等时候,横向光强分布与菲涅耳数没有关系。

环状光束通过透镜的聚焦特性研究

给出了环状光束在柱坐标系下的一种描述模型,并利用广义衍射积分理论,推导出环状光束经过近轴ABCD光学系统的传输公式·在此基础上,通过数值模拟方法定量分析了环状光束的聚焦光强分布以及焦面处的桶中功率·研究结果表明,环状光束的聚焦特性与光束阶数以及系统菲涅耳数有关;环状光束在实际焦面和几何焦面上的桶中功率均随着遮拦比的增大而降低,而随着系统菲涅耳数的增大而增大·在实际工作中,通过合理地选取系统菲涅耳数和光束遮拦比可以有效地控制环状光束聚焦后的光束质量·

环形区域上Zernike模式法波前重构

针对激光技术领域常见的环形激光光束 ,利用圆域 Zernike多项式和环域 Zernike多项式进行模式法波前重构 ,结果显示 :如果环形激光光束波前相位畸变主要由低空间频率成分组成 ,则可以直接利用圆域 Zernike多项式进行波前重构 ;如果环形激光光束波前相位畸变含有较多的高阶频率成分 ,则利用环域 Zernike多项式进行波前重构。