基于垂直偏振光成像法进行储存环束流垂直发射度测量的研究

For the recent 3rd generation light sources, the vertical emittance of a few pico-meter-radians which can be achieved with good coupling correction close to 0.1%, will lead to very small beam sizes. Several microns vertical beam size measurement has presented challenges for diagnostic capable in this region. Some traditional techniques including visible-UV light imaging, visible light interferometer and x-ray pinhole camera are difficult to measure such micro-level beam size. X ray based techniques like x-ray reflective optics, Fresnel zone plates optics and compound refractive lenses are more likely to make a precise measurement. However, it’s difficult to get a bigger improvement in the resolution, at the same time they need to build complex beam line and spend more on the expensive optics device. In this research topic, we present an idea of building an imaging system using the vertical polarized light, which including the vertical beam size information in the central valley between the two lobes. We can obtain the vertical beam size by comparing the valley-to-peak ratio with the theoretical model. A valley-to-peak ratio of about 2% is the estimated lowest detection limit of the monitor considering the rather low and smooth image background, a beam size about 3 μm could be measured.

对于最新设计的第三代同步辐射光源来说，当发射度耦合优化至接近0.1%时，储存环的垂直发射度可以达到若干pm•rad，这将获得截面尺寸非常小的束流。目前，对于微米量级的束流垂直尺寸进行测量非常具有挑战性。传统的几种方法，包括可见光成像法，可见光干涉法，X射线小孔成像法等都较难获得微米量级的分辨率；而X射线波段的掠反射镜聚焦成像法，菲涅尔波带片法，复合折射透镜法等需要建设复杂的束线、光学设备价格较为昂贵且在分辨率上无法较大幅度提升。本课题从现实需求出发，提出利用弯铁光源产生的垂直偏振光进行成像，像面上双峰间的波谷携带了束流垂直尺寸信息，通过建立同步光激发、传播模型，利用采集的波谷-波峰比值来计算束流垂直尺寸，进而求得垂直发射度。在像面噪声很低的情况下，可分辨出的最小比值达到2%时，可以测得接近3μm的束流。

随着同步辐射光源的发展，当发射度耦合优化至接近0.1%时，储存环的垂直发射度可以达到若干pm•rad，这将获得束流垂直尺寸为微米量级的束流。目前，对于微米量级的束流垂直尺寸进行测量非常具有挑战性。传统的几种方法，或是需要建设复杂的束线、光学设备价格较为昂贵，或是分辨率无法达到要求。本课题从现实需求出发，提出利用弯铁光源产生的垂直偏振光进行成像，像面上双峰间的波谷携带了束流垂直尺寸信息，通过建立同步光激发、传播模型，利用采集的波谷-波峰比值来计算束流垂直尺寸，进而求得垂直发射度。本项目严格按照研究计划和研究内容执行，完成了理论模型的建立、光学系统的设计与搭建、图像采集与处理软件的编写、在线实验研究等内容。得到了波谷-波峰比值的实时测量数据，并得到了束流垂直尺寸及垂直发射度。