Quality control of the CFRP mirror manufacturing process at NPF

TL;DR

This paper investigates the surface quality issues in CFRP mirror manufacturing, identifying dominant aberrations and proposing metrology techniques to improve surface quality and manufacturing processes.

Contribution

It introduces a comprehensive metrology approach combining optical and mechanical methods to analyze surface imperfections in CFRP mirrors.

Findings

Astigmatism is the dominant aberration in CFRP replicas.

Adding an extra resin layer reduces fiber print-through and surface roughness.

Residual irregularities remain after process improvements.

Abstract

The surface quality of replicated CFRP mirrors is ideally expected to be as good as the mandrel from which they are manufactured. In practice, a number of factors produce surface imperfections in the final mirrors at different scales. To understand where this errors come from, and develop improvements to the manufacturing process accordingly, a wide range of metrology techniques and quality control methods must be adopted. Mechanical and optical instruments are employed to characterise glass mandrels and CFRP replicas at different spatial frequency ranges. Modal analysis is used to identify large scale aberrations, complemented with a spectral analysis at medium and small scales. It is seen that astigmatism is the dominant aberration in the CFRP replicas. On the medium and small scales, we have observed that fiber print-through and surface roughness can be improved significantly by an extra resin layer over the replica's surface, but still some residual irregularities are present.