Quantifying height of machined steps on copper disk using Fourier domain short coherence interferometer

摘要

The internal shape and alignment of accelerator discs is crucial for efficient collider operation in the possible future compact linear collider. We applied a custom made and calibrated Fourier domain short coherence interferometer to measure the height of 40 and 60 μm machined steps on a copper disc in our laboratory. The step heights were determined to be: (43.0 ± 3.1) μm and (46.5 ± 3.2) μm for the 40 μm nominal step, and (46.6 ± 3.6) μm for the 60 μm nominal step. The errors represent 95% confidence level uncertainties and include uncertainty contributions from the calibration, refractive index of air, cosine error, and surface roughness. The step heights were validated by a calibrated contact stylus profilometer which resulted into (44.5 ± 0.8) μm and (45.9 ± 1.0) μrn for the 40 um nominal step, and (45.5 ± 1.7) μm for the 60 μm nominal step at 95% confidence level. The results show feasibility for noncontacting absolute shape and step height characterization with micrometer-level accuracy. This instrument is a first step towards a quality assurance tester for the accelerating structures of the compact linear collider.