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Spatial period is an important characteristic parameter in the design and fabrication of continuous phase plate (CPP). The smaller the minimum spatial period, the more freedom of CPP design and the more difficult of CPP manufacture. The minimum spatial period of continuous phase plate determines removal function size of tool in high-precision machining of continuous phase plate. Based on chemical reaction, atmospheric pressure plasma processing (APPP) is a non-contact and high efficiency material removal method. The removal function of APPP is nonlinear with dwell time because of chemical reaction rate affected by temperature. The dwell-time algorithm of variable removal function was proposed in order to solve the nonlinear removal function. APPP for fabrication of continuous phase plate with small spatial period is introduced in this paper. Finally, APPP with variable removal function dwell time algorithm was used to fabrication a continuous phase plate with spatial period of 8mm, surface peak-valley (PV) more than 790nm, wavefront gradient root-mean-square (RMS) of 1.07um/cm. The results show that residual surface error between designed surface and measured surface root-mean-square (RMS) is down to 50 nm. The variable removal function in APPP for fabrication of continuous phase plate with small spatial period is validated.
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