High-Accuracy Surface Topography Manufacturing for Continuous Phase Plates Using an Atmospheric Pressure Plasma Jet

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.

Jet morphology analysis of microwave‐generated plasma for microfabrication of optics

“…[1,2] When the fluorine-containing gas and additional oxygen are mixed into the inert gas, the generating plasma has the capability to etch quartz and other Si-based materials without producing mechanical damage, hence the microwave plasma jet can be employed for microfabrication of optics. [3][4][5][6] In the plasma etching processing of optics, the plasma jet morphology is critical for the processing accuracy and efficiency of optics, especially for optics with complex microstructure, because the length-diameter ratio of the plasma jet determines the actual processing resolution. However, due to the addition of fluorine-containing gas and oxygen, the working gas containing such molecular gas could be excited vibrationally or rotationally, ionized, or dissociated to form different radicals, causing the stability and controllability of the plasma jet to decrease.…”