Chromatic aberration theory in modern metrology
Hyperchromatic systems are especially used in chromatic confocal metrology to measure distances, layer thicknesses, and object surfaces. The correction of the spherical aberration for all wavelengths is an essential requirement for the design of such systems. We present general techniques for the methodical design of hyperchromatic systems with large longitudinal chromatic aberration. The proposed techniques are applied to design a contact-free wall thickness measuring device. Large tilting angles of up to 20° in combination with an extra long measuring range of 18mm and a minimum working distance of 35mm require a high speed optical system. We discuss the problems arising during the design of a system that realizes high lateral resolution within the whole measuring range. Furthermore we demonstrate the optimization of optical systems which image different wavelengths onto different image planes.
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