Abstract: The ion beam figuring method for optical mirrors with spiral scan mode is discussed. With the near-Gaussian property of the removal function, the figuring process can be simplified to a linear one and described by conventional computer controlled optics shaping (CCOS) principle. The modified Richard-Lucy iterative algorithm based on the Bayesian principle is adopted for the solution of dwell time. On the basis of analysis of the continuous velocity of dwell time, the criteria for determining the spiral path parameters are given. With these methods, the ion beam figuring technology with spiral scan mode is established. The figuring experiments on planar and aspheric samples are made, the final surface errors are both below 1/100λ. The experimental results show that spiral figuring is a deterministic method of high efficiency for optical mirrors, and can be used as the final figuring process, moreover the processing cost can be reduced.

Key words: Ion beam figuring, Richard-Lucy iterative algorithm, Spiral scan mode, Optical fabrication