Application of a long-trace profiler in situ at TPS beamlines

Abstract To achieve an ultrahigh-resolution with soft x-ray beamlines at the Taiwan Photon Source (TPS), the slope error of a highly precise grating must be at the level of 0.1 μrad (RMS) under thermal loading with various curvatures. Some optics generally operate under a high power density from an undulator magnet on a beamline. The thermal load introduces a thermal bump in the optics profile and degrades the beamline performance, such as the energy resolution and beam size. Hence, active X-ray mirrors are emerging as primary solutions to meet the performance requirements of TPS. First, active X-ray optics were assembled in the laboratory and bent to the desired surface using an in-house long-trace profiler (LTP). When the optics were installed in the beamlines, LTP in situ (ISLTP) was used to fine-tune the mirrors under various operating conditions. This paper introduces the design and construction of ISLTP with a precision of 0.1 μrad (RMS) developed to measure the mirror profile in soft x-ray beamlines. The ISLTP can provide feedback perturbations owing to localised heat loading from the X-ray beam and thermal changes in the ambient environment, and its performance and in situ measurements are presented.