Prisms and corner cubes
Prisms are multi-faceted, solid optics which are used to redirect light. The light entering a prism may reflect off one or several surfaces before exiting, or it may be refracted as it passes through the material due to the varying thickness of the prism body. Light passing through a right angle prism reflects off a single surface and is redirected 90 degrees from the incoming beam.
A corner cube retroreflector is a prism which returns an incoming beam directly toward its point of origin, regardless of the beam’s angle of entry. Corner cubes find widespread applications including satellite communications, surveying and range-finding and laser resonator cavities.
Manufacturers need to control both the surface quality of each face of a prism or corner cube as well as the relative angles between the faces. The challenges of measuring these optics are similar to those encountered when measuring flat optics: every facet in the optical path reflects some light back to the measurement system, resulting in a complex interferogram which is difficult or impossible to interpret. Measuring the front face of a prism proves particularly challenging as the extremely bright return signal can wash out the fringes altogether.
4D Technology’s AccuFiz SIS Fizeau dynamic laser interferometer uses a short coherence source that isolates the fringes for each face of a prism. Use the AccuFiz SIS to measure prism angles and faces—even the front face. The short coherence source also allows you to isolate fringes to measure corner cube surfaces, as well as measuring dihedral angle errors and retroreflection errors.
4Sight Software, included with all 4D interferometers, includes both corner cube and prism analyses that make it easy to characterize angles and faces of coated and uncoated prisms.
Homogeneity is a measurement of how much a specific glass optic’s refractive index deviates across its substance. Using our dynamic, short coherence interferometers, you can measure homogeneity more easily with three, not four, measurements. Plane-parallel flats without wedge can also be measured.
Parallelism is a measurement of how well aligned the two faces of a flat are to each other. For many optics, a wedge angle between the front and back surface is deliberately created to prevent the two surfaces from interfering. Both parallelism and wedge can be measured on 4D interferometers. Parallelism is particularly easy, using our short coherence source.
Added Technical Resources
Measuring a Corner Cube with AccuFiz
AccuFiz laser interferometer with 4Sight software makes it simple to characterize the errors in corner cubes, including angle error and retroreflection calculations.
Products for Prism & Corner Cube Measurement
Excels at fast, repeatable measurement of surface shape and transmitted wavefront error of flat and wedged optics. It is the most versatile Fizeau available, for any production environment.
Measures both sides of transparent, parallel optics as thin as 200 microns, surfaces in multi-surface optical systems, remote cavity test setups, and solid cavities such as etalons (laser rods).
NanoCam Sq systems measure surface roughness on coated and uncoated flats to ensure the quality of polishing processes.