Development of an in-vacuum long trace profiler for in situ measurement of optical components

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Abstract
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.
Funding Information
  • National Synchrotron Radiation Research Center (11362PT35)

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