Performance Evaluation Of Pitch Lap In Correcting Mid-spatial-frequency Errors Under Different Processing Parameters

Computer controlled optical surfacing(CCOS) is the main representative of modern optical manufacturing technology, which greatly improves the efficiency of optical processing. However, mid-spatial-frequency(MSF) errors are produced during CCOS processing. MSF errors are extreme resistance to many modern optical engineering.For the high-power laser systems, MSF errors can cause broadening of the central bright spot and the nonlinear self-focusing, also can reduce the brightness. So how to control MSF errors is an urgent task. Traditional evaluation such as PV, RMS and micro roughness can no longer describe such surface errors, and power spectral density function is a method to evaluate errors with the whole frequency range. The performance in correcting MSF errors are researched and analyzed. The work is as follows:Firstly, the influence of MSF errors to the optical element properties and the method to evaluate MSF errors are introduced. The meaning for pitch lap in suppressing MSF errors is described based on them.Secondly, the model and the basic theory of smoothing are introduced and analyzed. For the sinusoidal MSF errors, PV and RMS are converged exponentially through the band-pass filtering.Then, the motion model of smoothing is analyzed and the mathematical expression of removal function is derived. In order to check the accuracy and stability of the removal function, the removal function experiments are carried out and the experimental results are compared with the simulation results.A series of experiments are designed by orthogonal method. Then smoothing is done on the surface of plane mirrors. The diameter of the plane mirrors is 100 mm. The PV and RMS curve and power spectral density curve are analyzed through 2 ~ 10 mm band-pass filtering and the relationship of smoothing limit, rate and the parameters is also analyzed, based on those we can get the most optimal combination of parameters.Finally, the most optimal combination of parameters is applied to the smoothing of plane mirror and high-order aspherical mirror to verify the conclusion.