Parallel simply means that the distances between two surfaces, in this case the front and back planes of the glass component, are constant. If the surfaces were to extend theoretically to infinity, they would never converge.
In the world of glass components, perfect parallelism does not exist. Therefore, it is necessary to set required limits and measure for accuracy. Parallelism, also referred to as “wedge”, for glass components can be defined in several ways:
Transmitted Wavefront Error (TWE) is the degree of deviation seen in the wavefront when a beam is transmitted through an optical component. Although wedge/parallelism, power and irregularity all have the potential to contribute to total TWE, most definitions of TWE include only the irregularity component. For most components, Coresix can achieve ¼ wave per inch TWE.
Total Thickness Variation (TTV) is the difference between the minimum and maximum values of thickness over the clear aperture of the component. We determine this value using a scan pattern with a dual head laser accurate to 0.1µm and can achieve TTV’s of <1µm.
Arcs (Minutes and Seconds) A minute of arc (arcminute) is a unit of angular measurement equal to 1/60th of one degree. An arcsecond amounts to 1/60th of an arcminute. So, one arcsecond is equal to 1/3600 degrees of a full circle. Arcminutes and Arcseconds can be converted to degrees of deviation from perfect parallelism, both expressing the same measurement.