Lin Shang-Wei, Wang Duan-Jen, Fu Huang-Wen, Tsai Huang-Ming, Hua Chih-Yu, Kuo Chang-Yang, Hsu Ming-Ying, Kao Kai-Yang, Yin Gung-Chian, Fung Hok-Sum, Perng Shen-Yaw, Chang Chia-Feng
National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
Rev Sci Instrum. 2019 Feb;90(2):021716. doi: 10.1063/1.5055634.
To achieve an ultrahigh resolution of a beamline for soft X-rays at the Taiwan Photon Source (TPS), the profile of a highly precise grating is required at various curvatures. The slope error could be decreased to 0.1 µrad (rms) at a thermal load with a specially designed bender having 25 actuators. In the meantime, a long-trace profiler (LTP) was developed in situ to monitor the grating profile under a thermal load; it consists of a moving optical head, an air-bearing slide, an adjustable stand, and a glass viewport on the vacuum chamber. In the design of this system, a test chamber with an interior mirror was designed to simulate the chamber in the beamline. To prevent an error induced from a commercial viewport, a precision glass viewport (150CF, flatness 1/150 λ rms at 632.8 nm) was designed. The error induced from the slope error of the glass surface and the vacuum deformation was also simulated. The performance of the optical head of the LTP in situ (ISLTP) has been tested in the metrology laboratory. The sources of error of this LTP including the linearity and the glass viewport were corrected after the measurement. For the beamline measurement, an optical head was mounted outside the vacuum chamber; the measuring beam passed through the glass viewport to measure the grating profile in vacuum. The measurement of the LTP after correction of the above errors yielded a precision about 0.2 µrad (rms). In a preliminary test, an ISLTP was used to measure the grating profile at soft X-ray beamline TPS45A. The measured profile was for the bending mechanism to optimize the slope profile. From the measured energy spectrum, the slope error of the grating was estimated with software for optical simulation to be about 0.3 µrad (rms), consistent with our estimate of the ISLTP. In the future, it will be used to monitor the thermal bump under a large thermal load. In addition, an ISLTP was used to monitor the properties of optical elements-the twist and radius in the beamline during the installation phase.
为在台湾光源（TPS）实现软X射线光束线的超高分辨率，需要各种曲率下高精度光栅的轮廓。通过具有25个致动器的特殊设计的弯曲器，在热负载下斜率误差可降至0.1微弧度（均方根）。同时，现场开发了一种长跟踪轮廓仪（LTP）来监测热负载下的光栅轮廓；它由一个移动光学头、一个气浮滑块、一个可调支架和真空腔上的玻璃视窗组成。在该系统的设计中，设计了一个带有内部镜子的测试腔来模拟光束线中的腔室。为防止商业视窗引起的误差，设计了一个精密玻璃视窗（150CF，在632.8nm处平面度为1/150λ均方根）。还模拟了玻璃表面斜率误差和真空变形引起的误差。长跟踪轮廓仪现场光学头（ISLTP）的性能已在计量实验室进行了测试。测量后对该LTP包括线性度和玻璃视窗在内的误差源进行了校正。对于光束线测量，将一个光学头安装在真空腔外部；测量光束穿过玻璃视窗以测量真空中的光栅轮廓。校正上述误差后LTP的测量精度约为0.2微弧度（均方根）。在初步测试中，使用ISLTP测量了软X射线光束线TPS45A处的光栅轮廓。测量的轮廓用于弯曲机构以优化斜率轮廓。根据测量的能谱，使用光学模拟软件估计光栅的斜率误差约为0.3微弧度（均方根），与我们对ISLTP的估计一致。未来，它将用于监测大热负载下的热隆起。此外，在安装阶段，使用ISLTP监测光束线中光学元件的特性——扭曲和半径。
