Measurement Of Line Density Of Variable-line-space Gratings And Surface Shape Of Toroidal Mirrors

Heifei Advanced Light Facility(HALF)is a fourth generation synchrotron radiation light source based on a diffraction-limited storage ring.Its emittance and brightness reach advanced international level.As a bridge between the light source and experimental stations,a beamline is a booster for making good use of the excellent performance of the fourth generation synchrotron radiation light source in terms of extremely low emittance and high brightness.The quality of the optical components used in beamlines is a key factor in their performance,with variable-line-space(VLS)gratings and curved mirrors with multiple face shapes being the core optical components of beamlines and experimental stations.The quality of these optical components is particularly important.Therefore,it is urgent to explore techniques for the high-precision measurement of VLS grating line densities and small radius curved surface shapes.In response to the above requirements,based on the long trace profiler(LTP)system at National Synchrotron Radiation Laboratory(NSRL),this thesis proposes new methods for the line density measurement of VLS gratings by stitching measurement,and for measurement of curved surface shapes of mirrors coupled with a small aperture computer generated hologram(CGH)diffraction component.They meet the high accuracy requirements of HALF for measuring the line density of VLS gratings and the surface shape of curved reflectors.Key aspects include the following:1.A stitching method for measuring the line density of VLS gratings based on the LTP system is proposed,by adding the stitching function of the LTP system to the measured line density of VLS gratings.The inverse method is used instead of the previous method of processing data based on the angle of the rotary table.By the improved experimental method and new data processing method,the sources of the stitching errors introduced in the measurement is analyzed,and the corresponding method to suppress error is proposed.The repeatability of the results(Δ N/N)is better than 9.95 × 10-7(RMS),meeting the accuracy requirements(1×10-6(RMS))of grating line density measurements.2.A method combining the LTP system and a CGH is developed to measure the surface shape of toroidal mirrors and other curved mirrors,to meet the requirements of HALF for high-precision measurement of small curvature radius of curved surfaces.The structure of the corresponding CGH element is designed according to the surface shape of the mirror to be measured.This solution does not change the existing optical head system of the LTP system.The CGH module converts the plane wavefront of the measurement beam into certain wavefront which fits the surface shape of the mirror to be measured,enabling the measurement of meridional surface shapes of the toroidal mirror with a minimum radius of 89.7 mm,greatly extending the measurement capabilities of the existing LTP system.The repeatability of the improved LTP system is better than 30 nrad(RMS),meeting the measurement accuracy requirements and laying the foundation for the construction of HALF.