Plane-parallel optics are transparent components with parallel faces, or systems with two or more parallel surfaces. To measure plane-parallel optics with a laser interferometer can be challenging, as the parallel surfaces can all contribute interference fringes, making measurement extremely difficult or impossible.
4D's Surface Isolation Source is an optional, external laser source that excludes all but the surface of interest. Both surfaces of a transparent optic can then be measured, and transmitted wavefront error, optical thickness and homogeneity can be calculated. The adjustable path match mechanism provides flexibility, letting you dial in any surfaces that are within 88 through 112 millimeters from the aperture.
In a single setup you can measure both the front and back surfaces of an optic without repositioning it. Homogeneity, transmitted wavefront error and optical thickness can be readily obtained from a combination of measurements.
An AccuFiz equipped with SIS can perform all of the functionality of a standard AccuFiz as well as measuring plane-parallel optics. For example, you can use the Surface Isolation Source to measure the flat surface of a plano-convex lens, then switch to the internal source and add a transmission sphere to measure the spherical surface.