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Measuring Prisms and Corner Cubes

Optical Setups


Measuring a prism or corner cube is challenging because every facet reflects some light back to the measurement system. The result is a complex interferogram which is difficult or impossible to interpret.

A short coherence Fizeau interferometer such as the AccuFiz D isolates the fringes from each face, allowing you to:

  • verify the surface quality of the faces
  • calculate the dihedral angle errors and retroreflection errors, and
  • measure the transmitted wavefront error in single or double pass.

Measurement of solid, hollow, and porro prisms can be readily measured; more complex geometries (e.g., pentaprisms) may require different test arrangements.


Measuring a Corner Cube or Prism with a Short Coherence Fizeau Interferometer

measure corner cube, measure prism, optical setups, short coherence laser interferometer

Standard setup for measuring the surfaces and angles of a prism or corner cube.

corner cube measurement, single pass, double pass

Required Equipment

The diagram below shows the equipment needed to measure a prism or corner cube. The standard aperture for the AccuFiz D Fizeau interferometer is 100 mm or 150 mm, with beam expanders available up to 600 mm.
measure corner cube, measure prism, optical setups, short coherence laser interferometer
Required Components
AccuFiz D Interferometer More Information
Transmission Flat Specifications
2-Axis Base with Tip/Tilt Specifications
Shelf Mount Specifications
Return Flat Specifications


Want a convenient reference to this and other optical test setups? Download the Common Optical Testing Setups guide (PDF).

Other Considerations

Measuring High Reflectors

For highly reflective optics the test beam returned to the system may be so bright that it washes out the interference fringes. In this case, a beam attenuator such as a pellicle can be inserted into the test path to improve fringe contrast. An attenuation-coated transmission flat (available through 4D) can be used instead of a pellicle.

A pellicle can be used to reduce the return beam power from a highly reflective flat.

Measuring in Vibration

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.

The AccuFiz D interferometer features Dynamic Interferometry®, which enables all measurement data to be acquired simultaneously. Because acquisition speed is so fast, vibration is no longer an issue, and vibration isolation is not needed.

Measuring a Corner Cube with the AccuFiz®

Read more about the measurement process in this application note (PDF).


Measuring Prisms and Corner Cubes with a Fizeau Interferometer

A standard Fizeau interferometer can also be used to measure corner cubes and prisms. 

4D Technology AccuFiz Fizeau Laser Interferometer

Adding a short coherence Surface Isolation Source (SIS) module enables each surface to be measured without reflections from the other facets.

thin and plane-parallel surface error, flat surface error, optical setups, surface isolation source for accufiz fizeau interferometers

Need Assistance with Measuring Prisms or Corner Cubes?

Contact our applications staff today for expert opinions on optical measurement and on measurement equipment.

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