Zernike mapping of optimum dwell time in deterministic fabrication of freeform optics.

Wule Zhu,Anthony Beaucamp

doi:10.1364/oe.27.028692

Abstract

In optics fabrication technologies such as computer controlled optical surfacing (CCOS), accurate computation of the dwell time map plays an essential role in the deterministic performance of the fabrication process. However, it is still difficult for existing methods to derive smooth dwell time maps that reduce dynamic stressing on the machine especially at the aperture edge region, while retaining fine correction capability on freeform optics. To answer these challenges, we propose a new method based on Zernike decomposition and improved differential evolution optimization of the dwell time map, which can be applied to time-dependent optics fabrication processes such as fluid jet machining. Simulations and experiments based on a bi-sinusoidal freeform design were carried out to assess the feasibility of the proposed methodology. With appropriate fluid jet pressure, a bi-sinusoidal optical surface with demanding form error target of sub-100 nm in peak-to-valley was achieved, showing a remarkable improvement on the state-of-the-art, while keeping a good average surface roughness of 2.6 nm Ra on the optical glass.

Highlights

In recent years, there has been a rapidly increasing demand for an ever wider array of advanced optical systems, resulting in a strong need for accurate and efficient manufacturing of optics with complex shapes, especially freeforms [1]
Various computer-controlled optical surfacing (CCOS) methods have been developed over the past decades including magnetorheological finishing [4], elastic emission machining [5], fluid jet polishing [6], bonnet polishing [7], etc
A new approach for mapping the optimum dwell time was presented that enables ultra-precise generation of freeform optics by deterministic fluid jet (DFJ) fabrication

Summary

Introduction

There has been a rapidly increasing demand for an ever wider array of advanced optical systems, resulting in a strong need for accurate and efficient manufacturing of optics with complex shapes, especially freeforms [1]. Diamond tool based single point cutting is a deterministic optics fabrication method that can generate freeform optics with surface roughness of 5∼10 nm Ra [2], but it highly relies on the positioning accuracy of the machine and sharpness of the cutting tool [3]. Fluid jet polishing consists of pressurized slurry passing through a nozzle and removing materials by impingement of the workpiece, and is considered a versatile process for super fine finishing of small and complex components [8,9] It possesses a number of merits including: 1) absence of tool wear and edge effect due to the non-contact removal mechanism, 2)

Methods

Conclusion