Fabrication of continuous phase plate using atmospheric pressure plasma processing

Continuous phase plate (CPP) with complex surface structures is used to smooth the focal spot of laser beam. Great demand for CPP in laser fusion system requires mass production technology with low cost. Therefore, the rapid fabrication method for CPP using atmospheric pressure plasma processing (APPP) is presented in this paper. Firstly, the fundamental characteristics of APPP were studied to obtain the optimal processing parameters. Considering the influence on etching rate from surface temperature, trench machining experiments were conducted to establish the exponential model of influence function. Based on this model, the iterative calculation method for dwell time was developed to minimize the thermal effect on machining error, and the sinusoidal surface experiments prove its effectiveness. At last, a 320 mm × 320 mm × 2 mm CPP of BOROFLOAT33 (B33) with 2.78 μm PV was fabricated within 16 h using APPP, and the RMS of form error is 96 nm. The far field focal spot of the machined CPP was calculated. The result shows that the machined CPP has an acceptable beam-shaping function, which demonstrates the potential for fabricating CPP using APPP.