BRIGHT:the three-dimensional X-ray crystal Bragg diffraction code

In pursuit of a fully coherent X-ray free-electron laser(FEL), highly reflective Bragg crystals are used and will be used as a highly selective spectral filter in hard X-ray self-seeding FELs and X-ray FEL oscillators(XFELO), respectively. However, currently, when simulating self-seeding and XFELO, the three-dimensional effect of Bragg diffraction is not fully considered. In this paper, we derive a comprehensive solution for the response function of the crystal in Bragg diffraction. A three-dimensional X-ray crystal Bragg diffraction code, named BRIGHT, is introduced, which can be combined with other FEL-related codes, e.g., GENESIS and OPC. Performance and feasibility are assessed using two numerical examples,namely a self-seeding experiment for the linac coherent light source and XFELO options for Shanghai high repetition rate XFEL. The results indicate that BRIGHT provides a new and useful tool for three-dimensional modeling of FEL.

Mechanism of Bragg Diffraction-Assisted Light Extraction in GaN-based Light-Emitting Diodes Based on a Self-Consistent Model

By introducing the distribution of the light energy density in GaN-based light-emitting diode (LED),theLED model based on the incoherent regime and the light extraction efficiency are investigated.The energy density asa function of the angle of incidence is calculated to demonstrate the mechanism of the light extraction.The deviationbetween the tendencies of the transmissivity of the output layer and the extraction efficiency is also demonstrated.

Photoluminescence and X-ray Diffraction of Distributed Bragg Reflector

Spectral and structural characteristics of distributed Bragg reflector (DBR) in vertical-cavity surface-emitting lasers were studied with photoluminescence and double-crystal X-ray diffraction measurement.The expected high quality epitaxial DBR structure was verified.In the X-ray double-crystal rocking curves of DBR the zeroth-order peak,the first and second order satellite peaks were measured.Splitting of diffraction peak appeared in the rocking curves was analyzed.The effects of introduced deep energy levels on the structural perfection and optical properties were discussed.

Multifrequency Magneto-optic Bragg Diffraction and Radio Frequency Signal Parallel Processing

Magneto-optic(MO)coupling of guided optical waves with microwave magnetostatic waves(MSWs)simultaneously excited by multiple radio frequency(RF)signals can lead to multifrequency diffraction effects and then parallel processing of RF signals can be realized by using of the characteristics that diffraction efficiencies(DEs)are approximately in direct proportion to RF signals intensities and diffraction angles are related to frequencies of the corresponding RF signals within linear MO interaction region.In this paper,studied is the multifrequency MO Bragg diffraction in first-order MO interaction approximation,and obtained was the approximate analytical expression for principle diffraction efficiency(PDE).Also,put forward was a parallel imaging method of relative intensity of RF signals based on single-frequency diffraction.By calculation and analysis,it is shown that the relative error is not more than 0.3dB for the case of three RF signals within the frequency space of 60MHz.

An introduction to Bragg diffraction-based cold atom interferometry gravimeter

This paper presents a new type of cold atom interferometry gravimeter based on Bragg diffraction,w hich is able to increase the gravity m easurem ent sensitivity and stability of com m on Ram an atom gravim eters significantly. By com paring w ith Ram an transition,the principles and advantages of Bragg diffraction-based atom gravim eters have been introduced. The theoretical m odel for a tim e-dom ain Bragg atom gravim eter has been constructed. Som e key technical requirem ents for an n-order Bragg diffraction-based atom gravim eter have been deduced,including the tem perature of atom cloud,the diam eter,curvature radius,frequency,intensity,and tim ing sequence of Bragg lasers,etc. The analysis results are verified by the existing experim ental data in discussion. The present study provides a good reference for the understanding and construction of a Bragg atom gravim eter.

Bragg-Angle Diffraction in Slant Gratings Fabricated by Single-Beam Interference Lithography

A single-beam interference-lithography scheme is demonstrated for the fabrication of large-area slant gratings, which requires exposure of the photoresist thin film spin-coated on a glass plate with polished side-walls to a single laser beam in the ultraviolet and requires small coherence length of the laser. No additional beam splitting scheme and no adjustments for laser-beam overlapping and for optical path-length balancing are needed. Bragg-angle diffractions are observed as strong optical extinction that is tunable with changing the angle of incidence. This device is important for the design of efficient filters, beam splitters, and photonic devices.

静磁波变分计算与磁光Bragg衍射效率的提高

采用变分方法分析了垂直偏置磁场横向不均匀时掺Bi的YIG薄膜中微波静磁正向体波的激发和传播特性。计算了静磁正向体波对导波光的衍射效率,在静磁波的线性激发范围内计算结果与实验符合很好．处理方法可为线性磁光Bragg器件的优化设计提供理论指导．

一种基于声光Bragg衍射的信号处理系统

设计了一种基于声光 Bragg衍射的信号处理系统 ,给出了相应的实验框图和说明 ,分析了其主要性能。本系统最大的优点是可以方便地产生高精度的、能连续可调的延迟信号。在目标模拟、雷达干扰系统等方面有着极大的应用价值 ,同时还可以作为一个组件 。

X射线成像光学的新进展：Bragg－Fresnel多层膜元件

简要叙述了Ｘ射线反射式衍射光学元件──Ｂｒａｇｇ－Ｆｒｅｓｎｅｌ多层膜元件产生和发展的过程。介绍了它的基本原理及它的设计和制作步骤。对其应用前景作了简要分析，并对开展这方面的研究工作提出了一些设想。

光纤Bragg光栅的饱和效应(英文)

光纤 Bragg光栅的饱和效应可引起二阶衍射 ,并使一阶衍射的峰值反射率下降 .本文利用折射率变化模型和耦合模理论 ,模拟了饱和情况下 Bragg光栅的一阶和二阶衍射谱 ,并讨论了饱和系数对一阶和二阶衍射的 Bragg波长和峰值反射率的影响 .数值模拟结果与参考文献中的实验结果相吻合 .

基于Bragg衍射的声光频谱分析仪

针对其他测频器件的缺陷,提出了基于Bragg衍射的声光频谱分析法,介绍了它的主要工作原理,研制出了信号处理软硬件设备,通过试验和仿真,实现了对电磁频谱进行实时并行检测分析。采用声光频谱分析制成的声光Bragg接收机能够在复杂的电磁环境中同时快速检测出多束射频电磁波。该机瞬时带宽可达1 GHz,对单个脉冲的截获率约为100%,灵敏度可达-80 dBm,测频分辨率可达1 MHz。在电子战中有很高的应用价值。

X射线Bragg-Fresnel元件中衍射图形制作技术研究

本文研究Ｘ射线Ｂｒａｇｇ－Ｆｒｅｓｎｅｌ元件中衍射图形的制作技术。介绍了衍射图形制作技术方案的确定，金属吸收层厚度的计算，制作技术工艺流程及衍射图形测试结果。

软X射线Bragg-Fresnel二维聚焦镜的设计理论和方法

Ｘ射线Ｂｒａｇｇ－Ｆｒｅｓｎｅｌ元件是近十年发展起来的一种用于Ｘ射线波段的新型光学元件。本文介绍一种具有二维聚焦效能的Ｂｒａｇｇ－Ｆｒｅｓｎｅｌ元件的设计理论和方法。设计中采用衍射理论并用Ｃ语言编制计算机程序系统对衍射图形进行设计。对于使用波长１３．８ｎｍ，入射角５°，使用焦距２００ｍｍ的使用条件，设计结果为３５Ｍｏ／Ｓｉ双层多层膜，周期厚度７．１４ｎｍ，理论反射率约为６０％；衍射图形共４００个环带，最内环半宽度５２．５μｍ，最外环宽度１．３μｍ。

不均匀磁化薄膜中静磁波对导波光的Bragg衍射

研究了横向不均匀偏置磁场作用下掺Bi的YIG薄膜中微波静磁波的激发和传播特性;采用变分方法计算了静磁正向体波的色散关系和交变磁化强度,分析了不均匀场对静磁波-导波光耦合的影响·理论计算得到的衍射效率曲线与实验结果基本一致,表明适当不均匀场可以大大提高磁光Bragg器件的衍射性能·

超短脉冲激光经透射型体Bragg光栅的时域特性

利用Kogelnik耦合波理论对超短脉冲激光经透射型体Bragg光栅的时域衍射特性进行了研究,讨论了透射型体Bragg光栅的群延迟色散和光栅结构参数之间的关系,分析了群延迟色散和频谱剪切对衍射脉冲时域强度分布的影响.结果表明:当入射超短脉冲脉宽为100fs时,经透射型体Bragg光栅衍射后的脉冲展宽主要源自光栅对入射脉冲的频谱剪切,当入射超短脉冲脉宽为10fs时,衍射脉冲的展宽量不仅受频谱剪切的影响,而且与光栅的群延迟色散密切相关.

Bragg反射齿型平面凹面衍射光栅性能研究

本文基于Bragg反射光栅是一维光子晶体的一种特例结构,提出利用一维光子晶体理论进行Bragg衍射光栅的设计并对其性能进行研究分析.根据一维光子晶体理论,建立了罗兰圆结构的凹面椭圆Bragg蚀刻衍射光栅,研究了TE/TM模式下器件的分光特性以及入射角度改变对器件角色散造成的影响;同时,文中对比了空气介质型和金属铝线型椭圆Bragg蚀刻衍射光栅的光学性能.研究结果表明:选择合适的器件参数,可以实现TE/TM模式下1.465—1.615μm范围内波长衍射效率在95%以上,且空气介质型结构光栅的通道均匀性要优于金属铝线型结构光栅;入射角在30?—60?范围内变化时,相同入射角度下,TM模式下器件角色散大于TE模式.基于Bragg衍射光栅设计的波分复用器是一种尺寸小、衍射效率高的新型EDG波分复用器,为未来密集型EDG波分复用器发展提供了一种新的设计思路.

固体中的原子相关性和Bragg衍射

提出一个描述固体结构的新方法——原子相关性方法。给出原子相关性、相关性基矢、相关性格子及其倒格子的定义，分析对比原子相关性在晶体、准晶和非晶中的不同表现。从原子相关性出发讨论了固体的衍射问题。

光折变晶体中平面光栅的构建与研究

光折变效应在全息存储和处理方面具有重要的应用价值,光折变晶体中的全息光栅特性直接影响信息处理的质量和速度.本实验通过理论分析,计算得出Raman-Nath平面光栅的制作参量,设计实验系统并测量了LiNbO 3晶体中平面光栅的多级衍射性质,讨论了多级衍射效率和其空间分布特征.实验设计基于学生的光学知识和实验技能,向非线性光学知识和科学思辨创新方法拓展,在可调光分束器、图像处理等方面具有潜在的应用价值.

Revealing the residual stress distribution in laser welded Eurofer97 steel by neutron diffraction and Bragg edge imaging

Eurofer97 steel is a primary structural material for applications in fusion reactors. Laser welding is a promising technique to join Eurofer97 plasma-facing components and overcome remote handling and maintenance challenges. The interaction of the induced residual stress and the heterogeneous microstructure degrades the mechanical performance of such fusion components. The present study investigates the distribution of residual stress in as-welded and post-heat treated Eurofer97 joints. The mechanistic connections between microstructure, material properties, and residual stress are also studied. Neutron diffraction is used to study the through-thickness residual stress distribution in three directions,and neutron Bragg edge imaging(NBEI) is applied to study the residual strain in high spatial resolution.The microstructures and micro-hardness are characterised by electron backscatter diffraction and nanoindentation, respectively. The M-shaped residual stress distribution through the thickness of the as-welded weldment is observed by neutron diffraction line scans over a region of 1.41 × 10 mm^(2). These profiles are cross-validated over a larger area(∼56 × 40 mm^(2)) with the higher spatial resolution by NBEI. The micro-hardness value in the fusion zone of the as-welded sample almost doubles from 2.75 ± 0.09 GPa to 5.06 ± 0.29 GPa due to a combination of residual stress and cooling-induced martensite. Conventional post weld heat treatment(PWHT) is shown to release ∼90% of the residual stress but not fully restore the microstructure. By comparing its hardness with that of stress-free samples, it is found that the microstructure is the primary contribution to the hardening. This study provides insight into the prediction of structural integrity for critical structural components of fusion reactors.

DEVIATION FROM BRAGG LAW AND EDGE EFFECT IN DOUBLE-CRYSTAL DIFFRACTION

A more precise expression for the angular deviation from the Bragg law and the angularrange of X-ray diffracted by perfect crystal are derived. The critical angle of the total re-flection of X-ray from the surface of crystal is obtained naturally by the new expressions,which well coincides with that deduced in optics in consideration of the refraction. Twopeaks appear on the rocking curve when X-rays shoot at the surface at a small glancing angleand simultaneously on the side of crystal although the double-crystal is in (n, -n) setting,which is called the "edge effect". The angle between these two peaks on the rocking curvecan be used to measure the number of electrons in an unit cell of crystal.