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Abstract:

In the measurement of surfaces as they are used and needed optics manufacture, many aspects of traceability and uncertainty arise. The route to traceability from a surface to ultimately the speed of light that defines the unit of length: the metre, is not at all straightforward. This presentation highlights some common aspects of traceability and uncertainty that are present in any surface measurement. Some of these may be obvious, such as the surface height that may be calibrated by step height standards. The traceability route to an absolute flatness reference is already less straightforward and the matter becomes really complicated when aspects such as surface filtering, bandwidth, parameter calculation, and measurement noise must be taken into account. In this presentation an overview of calibration methods and artefacts will be presented, in combination with related aspects of traceability and uncertainty estimations. It will also be explained how a common framework is being made in ISO standards that define a set of typical metrological characteristics that are common for any surface measuring instrument. However these standards even define the calibration methods, the route to a full uncertainty evaluation is not yet straightforward and open to interpretation. Some methods will be given that can be applied to both optical and mechanical surface measurement. Essential in any approach is a solid theory and measurement model of the probe-surface interaction, that is more or less available for mechanical measurements and under development for optical measurements. The presentation concludes with an outlook to further research.