Continuous phase plate (CPP) has been widely used in high energy laser optical systems such as inertial confinement fusion (ICF) due to its high energy efficiency and easy control of focal spot shape. At present, Magnetorheological Finishing (MRF) technology is one of the main means to realize CPP high precision processing. This paper analyzes and optimizes the error factors that affect the accuracy improvement in CPP machining process, such as tool path, removal function characteristics, positioning accuracy and material removal amount. The main error source surface shape matching error is analyzed and the frequency domain cross-correlation matching algorithm based on Fourier transform is used to realize the sub-pixel level height between the actual wavefront and the theoretical design wavefront accurate registration. Based on the results of process optimization, the high-precision processing of CPP with the design feature size of 10 mm, the peak to valley (PV) of 1 λ (λ = 1053nm) and gradient rms of 0.82 λ/cm was processed with MRF technology. Through the iteration of two processing stages, the matching accuracy between the processing wavefront and the theoretical wavefront is controlled at 10.5nm (root mean square, RMS), which lays the foundation for CCP processing with larger diameter and smaller cycle.
Continuous phase plate (CPP) is an important diffractive optical element, which is widely used in high power laser devices. The continuous phase plate with a small aperture period of 4 mm is processed by the atmospheric pressure plasma polishing (APPP). Through the study of the reaction mechanism, it is found that the removal volume has a non-linear relationship with the dwell time, which will lead to machining errors. Based on this, a dwell time compensation method is proposed, and the machining program is generated according to this relationship. A 70mm × 70mm × 20mm continuous phase plate was fabricated by using the processing program generated by this method. The processing time was 4.5h, and the surface residual converged to 57.188nm RMS. The experimental results show that the method can effectively calculate the removal function under different dwell time, and significantly improve the machining accuracy.
High-precision aspheric components are widely used in modern systems with the capability of high image quality, but an high-slope convex aspheric aspheric surface is more challenging to fabricate because of its more complex shape and measuring difficulty compared with other surfaces. As the traditional aspheric surface manufacturing will cause many problems like the tools cannot conform to the local varying curvatures of high slope convex aspheric optics. In this paper, a high efficient approach include CNC generating, MRF fine polishing and multi-wavelength interferometer measurement to get a high-precision convex aspheric surface is presented. A kind of flexible tools was designed to polish the surface and correct MHSF errors on the aspheric surface which can always conform to the surfaceduring the process. And the pressure needed during the polishing process is simulated by COMSOL software. A high-precision convex aspheric surface is successfully obtained and the final surface RMS is better than λ/30.
Smoothing is a convenient and efficient way to correct mid-spatial-frequency errors. Quantifying the smoothing effect allows improvements in efficiency for finishing precision optics. A series experiments in spin motion are performed to study the smoothing effects about correcting mid-spatial-frequency errors. Some of them use a same pitch tool at different spinning speed, and others at a same spinning speed with different tools. Introduced and improved Shu's model to describe and compare the smoothing efficiency with different spinning speed and different tools. From the experimental results, the mid-spatial-frequency errors on the initial surface were nearly smoothed out after the process in spin motion and the number of smoothing times can be estimated by the model before the process. Meanwhile this method was also applied to smooth the aspherical component, which has an obvious mid-spatial-frequency error after Magnetorheological Finishing processing. As a result, a high precision aspheric optical component was obtained with PV=0.1λ and RMS=0.01λ.