The Method of Multi-Scale Removal Function Composite Processing CPPs Based on Magnetorheological Finishing

Continuous Phase Plates (CPPs) are pivotal optical components for the precise control of laser beams in inertial confinement fusion. However, their random surface morphology, progressively diminishing spatial period structures, and increasingly substantial modulation depths pose significant challenges in manufacturing. Magnetorheological Finishing (MRF), characterized by its non-sub-surface damage and deterministic material removal, has emerged as the predominant method for CPP fabrication. Nonetheless, traditional processes reliant on a single-sized removal function in an iterative "processing-measurement-processing" cycle to achieve the target surface profile encounter a dilemma in balancing precision and efficiency. Addressing this issue, this study experimentally investigates the impact of varying removal function sizes on the efficiency and accuracy of CPP fabrication. A novel multi-sized removal function combination approach for CPP processing is proposed. Initially, a simulation analysis based on the two-dimensional convolution removal principle is conducted to validate the feasibility of this method. Subsequently, experimental processing of a standard surface profile with a peak-to-valley (PV) value of 4.398λ (λ=632.8nm), a surface RMS of 623.477nm, and a minimum spatial period of 14mm is performed. The process achieves a residual error RMS of 35.4nm within 219 minutes. Compared to the large-sized removal function process, the precision is enhanced to the level of the small-sized removal function process, while the efficiency is improved by approximately 21% compared to the small-sized removal function process. This study provides a foundational basis for the MRF processing of larger-aperture CPPs.