Fabrication of Optical Components by Ultraprecision Finishing Processes

Abstract

The demand of ultraprecision optical components is increasing extensively with the rapid development of the modern optics. The optical components used in X-ray microscopy and extreme ultraviolet lithography (EUVL) demand surface roughness of about 0.1 nm rms, a figure accuracy about 1 nm peak-to-valley (p–v) and no induced subsurface crystallographic damage. Furthermore, an aspherical surface is gaining more interest over the past few years for its favourable properties, and many new optical materials are also being developed. Fabrication of ultraprecision optical components became a great challenge to the optical fabrication industry. Aspheric optical components are generally fabricated by shaping methods followed by precision finishing processes. Near net shape of the component can be accomplished by the shaping methods (e.g. single-point diamond turning, deterministic micro-grinding, etc.). The application of optical components fabricated by this method is limited to the infrared (IR) optics owing to the presence of high-spatial-frequency surface irregularities which lead to the possibility of scattering for shorter wavelength applications. Desired surface finish, figure accuracy and surface integrity can be attained by precision finishing techniques to make it suitable for shorter wavelength applications. In the recent years, ion beam figuring, elastic emission machining, nanoparticle colloid jet machining and magnetorheological finishing are extensively used for fabrication of ultraprecision optics. In this chapter, principle mechanism of material removal and applicability of aforementioned ultraprecision finishing processes to different materials are discussed.