In this paper, a monotonic-increasing-thickness model (MITM) is proposed for designing cylindrically diffractive focusing micromirrors (DFMs) and cylindrically diffractive focusing micromirror arrays (arrayed DFMs). Based on rigorous electromagnetic theory and the boundary element method, numerical results reveal that focal properties of the designed DFMs are significantly improved through replacing the traditional equal-thickness model (ETM) with the proposed MITM, especially in the case of small <i>f</i>-numbers. In addition, the superiority of the MITM to the ETM is demonstrated in designs of the arrayed DFMs. For interference effect in the arrayed DFMs, we present new explanations.
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