< back to main site

Publications

A new approach for establishing a reference plane for absolute measurement of shape and flatness with nanometre precision.

Virdee, M (1993) A new approach for establishing a reference plane for absolute measurement of shape and flatness with nanometre precision. NPL Report. MOM 114

[img] Text
mom114.pdf

Download (14MB)

Abstract

An alternative optical method to interferometry has been developed to measure form of flat and of shallow curvature optical surfaces to nanometre accuracy without reference to a master surface. The method consists of measuring the surface slopes at points along a line with a resolution of 1/100 of a second of arc. Slope values are integrated with respect to distance to obtain profile height. The surface is scanned with a laser beam whose direction and straightness can be maintained to a high degree of accuracy by using enclosures that insulate the acoustic noise and improve the thermal stability to better than 0.1 °C. The line profiles measured in X and Y directions are combined using a least-squares solution to obtain a complete surface map and reference plane. The calculated reference surface is further corrected for twist by measuring the diagonal profiles. Recent measurements using a new two-dimensional profilometer system have shown that it can repeatably measure shape over an area of 120 x 120 mm to within ­± 2 nanometres with angular deviations from flatness of up to 5 minutes of arc. This profilometer has a capability of readily examining surfaces with specular reflectivities varying from 4% to 100% up to 200 rnrn in diameter. Recently an assessment of systematic uncertainties of the two-dimensional instrument has been made by comparing flatness results with those obtained by Fizeau and Zygo interferometry, and the two sets of measurements agree to within ± 5 nanometres. The slope integration method has the potential to be developed further to characterise non-specular diffusing and specular surfaces over an area of at least 400 x 400 mm.

Item Type: Report/Guide (NPL Report)
NPL Report No.: MOM 114
Subjects: Engineering Measurements
Engineering Measurements > Dimensional
Last Modified: 02 Feb 2018 13:19
URI: http://eprintspublications.npl.co.uk/id/eprint/342

Actions (login required)

View Item View Item