Specifying Wavefront Or Surface Error In Aspheres

By Flemming Tinker, President, Aperture Optical Sciences

The optical quality of aspheric mirrors is commonly specified by their surface accuracy and reflected wavefront error. The surface error is the deviation of the surface from its perfect form, while the wavefront error is the deviation of the resulting reflected or transmitted wavefront from its perfect shape. It is often assumed that these tolerances are related to each other by a simple scale factor. However, that is not the case when it comes to aspheric mirrors. This application note compares surface accuracy measurements with wavefront error measurements, and provides an application example on using them in off-axis parabolas.