Abstract
The continuous phase plate (CPP) is the vital diffractive optical element involved in laser beam shaping and smoothing in high-power laser systems. The high gradients, small spatial periods, and complex features make it difficult to achieve high accuracy when manufacturing such systems. A high-accuracy and high-efficiency surface topography manufacturing method for CPP is presented in this paper. The atmospheric pressure plasma jet (APPJ) system is presented and the removal characteristics are studied to obtain the optimal processing parameters. An optimized iterative algorithm based on the dwell point matrix and a fast Fourier transform (FFT) is proposed to improve the accuracy and efficiency in the dwell time calculation process. A 120 mm × 120 mm CPP surface topography with a 1326.2 nm peak-to-valley (PV) value is fabricated with four iteration steps after approximately 1.6 h of plasma processing. The residual figure error between the prescribed surface topography and plasma-processed surface topography is 28.08 nm root mean square (RMS). The far-field distribution characteristic of the plasma-fabricated surface is analyzed, for which the energy radius deviation is 11 μm at 90% encircled energy. The experimental results demonstrates the potential of the APPJ approach for the manufacturing of complex surface topographies.
Highlights
High-powered laser systems require precise control of the laser beam shape and energy distribution in the target plane [1]
Menapace et al [5] developed the magnetorheological finishing (MRF) technique to fabricate large-aperture continuous phase plate (CPP) for the National Ignition Facility (NIF), in which the spatial periods of the surface topography are usually larger than 4 mm and the PV values are as high as 8.6 μm [6,7]
All figuring experiments were performed in our self-developed atmospheric pressure plasma jet (APPJ) system
Summary
High-powered laser systems require precise control of the laser beam shape and energy distribution in the target plane [1]. The continuous phase plate (CPP), as a beam-shaping optical element, can manipulate the incident laser to allow beam shaping and smoothing with complex surface topographies [2]. The surface topography of the CPP, having multiple spatial scales, high peak-to-valley (PV) values, large gradients, and high accuracy, causes much difficulty in fabrication [3]. Subaperture technology is mainly used to imprint the topography deterministically to obtain CPP elements [4]. Menapace et al [5] developed the magnetorheological finishing (MRF) technique to fabricate large-aperture CPPs for the National Ignition Facility (NIF), in which the spatial periods of the surface topography are usually larger than 4 mm and the PV values are as high as 8.6 μm [6,7].
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