Accurate Measurement of Surface Irregularities for a Standard Sphere Using Fizeau Laser Interferometer

Document Type : Original Article

Authors

1 Engineering and Surface Metrology Laboratory, National Institute of Standards (NIS), Giza, Egypt

2 Physics Department, Faculty of Women for Arts, Science, and Education, Ain Shams University, Cairo, Egypt

Abstract

Spherical surfaces are essential components in optical systems for different applications. Also, standard ‎spheres are typically employed to calibrate dimensional and mass-measuring instruments. Therefore, ‎measuring and eliminating the surface irregularities of these spheres represents a challenge for modern ‎industries. Surface irregularities can be measured by either the contact method (as stylus profilometers) ‎or the non-contact method (as interferometers). The Fizeau laser interferometer (GPI-XP, Zygo Co.) is ‎typically used to accurately measure surface irregularities for flat surfaces, lenses, and mirrors of 102 mm ‎diameter, and it is not prepared for testing heavy spheres. This work presents a modification for the ‎interferometric system to expand its capability for testing spheres of diameters up to 145 mm and masses ‎up to 2 kg. Also, the modification provides automatic rotation for the tested surfaces (an electric rotating ‎platform) to avoid the disadvantages of manual rotation (a tweezer). At different rotation angles, the ‎measurements are performed on a mass-standard silicon sphere (SiScKg-02-d, PTB Inst.). The average ‎measured value of the surface irregularities is 43.9 nm, with an improved repeatability of 2.8 nm and a ‎minimized measurement uncertainty of ±6.8 nm. The evaluation of the uncertainty budget is also ‎investigated in this study.‎

Keywords

Journal of Scientific Research in Science

Articles in Press, Corrected Proof
Available Online from 26 July 2023

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