Low coherence interferometer for metrology of liquid-jet polishing of LIGO optics

Abstract

Accurate surface measurement is very important when making high-quality optical components, such as those used in the LIGO experiment for detecting gravitational waves. Liquid Jet Polishing (LJP) is one of the promising techniques that can achieve high surface quality by removing the residual errors from the polished surface. For this, it uses pressurized liquid slurry of abrasive fluid for time dependent removal of material from the surface. To achieve precision optics it is utmost important to have a suitable measurement system that can provide the residual errors present in the optics accurately. In view of this a diffraction phase interferometer was developed that can provide nanometer scale the surface map across the sample surface. This thesis explains the development of a Low Coherence based Diffraction Phase Imaging (DPI) system to measure surface profile of the sample under test. The DPI system was built using a Super luminescent Diode (SLD) as a low-coherence light source. It included a custom 4f imaging system and a pinhole to filter the light and capture clear phase information. Along with this, a prototype Liquid Jet Polishing (LJP) setup was also developed to generate the test samples that can be used to image using DPI system. Efforts were also made to assess the effect of important parameters such as nozzle size, slurry pressure, distance between nozzle and surface, and the movement speed of the sample stage.