The oblique incidence is a crucial metrology method to realize the measurement demand for high aspect ratio multiple elements piezoelectric X-ray bimorph mirror surface by small-aperture Fizeau interferometers in one single shot. Due to the change of optical path difference in oblique incidence, we analyzed how different oblique incidence angles would affect the results of the surface height with numerical simulation and evaluated angular errors when curved mirrors are measured. Then we constructed an oblique incidence measurement system for measuring the 200 mm X-ray bimorph mirror with multiple elements piezoelectric by using a 100 mm clear aperture Fizeau interferometer and return reference mirror based on a preliminary determination of the angle of oblique incidence, and so the precise angle of oblique incidence is calculated from the actual measurement results. The oblique incidence can directly observe the dynamic effects of a high aspect ratio X-ray bimorph mirror surface in response to the applied voltages. With practical interferometric measurements of the multiple elements piezoelectric X-ray bimorph mirror by the constructed oblique incidence measurement system, and we obtained multiple sets of response functions and optimized surface at different voltages. Furthermore, the bimorph mirror surface optimized height profile was experimentally controlled and measured to be 17.13 nm PV (peak to valley) at the centerline, which can lay the foundation for measuring the X-ray bimorph mirror surface with extremely high aspect ratios.
Gold-coated photoresist grating (GCPG) is commonly employed in high-power femtosecond laser systems for its broadband and simple structure. The pyrolysis and low heat conductivity of photoresist substrates are well known to result in a low GCPG laser damage threshold, which restricts the power increase of laser systems. Gold-coated fused silica grating (GCFSG) has a high threshold potential since the grating pattern is transferred from the photoresist to the fused silica substrate by etching. In this paper, a rectangular GCFSG with a period of 1740 l/mm was designed and fabricated. Using rigorous coupled-wave analysis (RCWA), the ideal slot form for GCFSG with high diffraction efficiency was designed. After a comprehensive analysis of the impact of gold plating coating flaws on efficiency, iterations of the coating process were carried out to optimize the slot shape. For these GCFSG samples, magnetron sputtering was used as the gold deposition process and the samples had a bandwidth of at least 150 nm with the -1st-order diffraction efficiency of 93% around the central wavelength of 800 nm. The measured efficiency results were compared with our simulation calculations and good agreement was achieved. After being damaged by lasers, GCFSG can be reused with good economics by being cleaned and then gold-coated.
The beamline optical system in the fourth generation synchrotron radiation light source and free-electron laser facilities puts forward harsh requirements on the performance of optical components, among which, the bimorph mirror is an adaptive optical component designed to meet the ultra-high surface shape progress regulation of the component and the wavefront compensation of the beamline. Domestic design and processing of bimorph mirror technology is still in urgent need of technical breakthroughs. To address this issue, we have studied the fabrication process of bimorph mirror, analyzed the design of the brake unit size in the bimorph mirror and the influence of the mirror clamp support method on the deformation process.
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