Surface Error of Convex Optical Surfaces

Overview

Verifying the surface quality of convex lenses, mirrors, domes, and telescope secondary optics is typically accomplished with a Fizeau Laser Interferometer. A short coherence laser interferometer can also be used, and it is the preferred option for measuring thin domes.

A vertical configuration can speed measurements, particularly for repeated measurements of the same type of component. The lightweight AccuFiz interferometer and lookdown stand make vertical measurement easy.

For highly reflective optics the test beam returned to the system may be so bright that it washes out the interference fringes. A beam attenuator such as a pellicle can be inserted into the test path to improve beam contrast. A reference optic with attenuation coating can also be used.

With a traditional, phase-shifting interferometer, measurement data is acquired sequentially—a long enough process that vibration and air turbulence will degrade or even prevent measurement. The interferometer and all mounts must be situated on an air table to isolate the system from vibration.  Air isolation can be expensive—prohibitively expensive for very large optics or long measurement paths.

4D AccuFiz interferometers feature optional Dynamic Interferometry^®, which enables all measurement data to be acquired simultaneously. Vibration is no longer an issue, and an isolation table is not needed.