Lin Shang-Wei, Chiu Chao-Chih, Hsu Ming-Ying, Chang Chia-Feng, Chen Bo-Yi, Yin Gung-Chian
National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
Rev Sci Instrum. 2025 Sep 1;96(9). doi: 10.1063/5.0256054.
In this work, we developed a vacuum-compatible long trace profiler (LTP) for in situ metrology of ultra-precise x-ray optics within synchrotron vacuum chambers. Although traditional LTPs operate ex situ under atmospheric pressure, earlier optical setups-such as that by Qian et al.-performed in situ distortion measurements by directing laser beams through vacuum viewports. While these configurations enabled in situ monitoring of mirror deformation, their accuracy was constrained by optical distortions from vacuum windows and by beam deviations caused by air turbulence. To overcome these limitations, we developed a fully in-vacuum LTP system installed directly inside the vacuum chamber, fully compatible with ultrahigh vacuum (UHV) conditions (<1 × 10-8 Torr). Based on the original Takacs LTP design, the system incorporates a vacuum-compatible CMOS sensor, an external laser to reduce heat and weight, and a motorized four-axis alignment stage. This system is designed to measure low-spatial-frequency slope error, which is critical for evaluating optical figure quality. Performance was validated under identical atmospheric conditions using a conventional LTP for comparison. Under identical conditions, the in-vacuum LTP measured slope errors of 100 nrad RMS (flat) and 200 nrad RMS (curved). However, measurable deviations in curvature radius and coma coefficient were observed, attributed to stage wobble and lens aberrations. These findings confirm baseline performance and demonstrate the system's feasibility for UHV-compatible slope metrology. The in-vacuum LTP is intended to support real-time slope monitoring and feedback correction of active optical components during operation at synchrotron beamlines.
在这项工作中，我们开发了一种与真空兼容的长跟踪轮廓仪（LTP），用于同步加速器真空室内超精密X射线光学元件的原位计量。尽管传统的LTP在大气压力下进行非原位操作，但早期的光学装置——如钱等人的装置——通过将激光束穿过真空视窗来进行原位畸变测量。虽然这些配置能够对反射镜变形进行原位监测，但其精度受到真空窗口的光学畸变以及空气湍流引起的光束偏差的限制。为了克服这些限制，我们开发了一种完全安装在真空室内的真空LTP系统，该系统与超高真空（UHV）条件（<1×10-8托）完全兼容。基于最初的塔卡克斯LTP设计，该系统集成了一个与真空兼容的CMOS传感器、一个用于减少热量和重量的外部激光器以及一个电动四轴对准平台。该系统旨在测量低空间频率斜率误差，这对于评估光学面形质量至关重要。使用传统LTP在相同的大气条件下对性能进行了验证以作比较。在相同条件下，真空LTP测量的斜率误差为均方根值100纳拉德（平面）和200纳拉德（曲面）。然而，观察到曲率半径和彗差系数存在可测量的偏差，这归因于平台摆动和透镜像差。这些结果证实了基线性能，并证明了该系统在与超高真空兼容的斜率计量方面的可行性。真空LTP旨在支持同步加速器光束线运行期间有源光学元件的实时斜率监测和反馈校正。
