Twyman-Green Interferometer

 What is a Twyman-Green Interferometer?

A Twyman-Green interferometer is a laser interferometer configuration used for measuring the surface shape and transmitted wavefront quality of optical components, assemblies, systems, and optical-grade mechanical surfaces.

In a Twyman-Green laser interferometer,  a source beam is collimated, then divided by a beam splitter. The “reference beam” is directed to a high-quality reference mirror. The “test beam” is directed to the test surface. The test wavefront can be shaped to match the concave/convex curvature of the test surface or system by using a diverging lens or beam expander.

Advantages of a Twyman-Green Interferometer

Twyman-Green interferometers have several key advantages over other types of interferometers.

Measure in Difficult Locations

The compact optical design makes for a small measurement head, which is easy to position in tight spaces. The laser source can be coupled to the head via a fiber optic cable, which moves heat-generating elements away from the optics. The combined result: easy positioning in challenging locations.

Measure Despite Vibration, Without Isolation

With a dynamic PhaseCam interferometer, vibration isolation is not required. This advantage is particularly critical when measuring large optics, or when measuring over long paths, where isolation systems would be prohibitively expensive. The interferometer does not even need to be coupled to the test optic, further simplifying setup.

Measure Without an Expensive Reference

With a Fizeau interferometer,  expensive, high quality reference transmission (flat or spherical) optics are required. The Twyman-Green interferometer does not require this external reference optic.

Operate Remotely

Motorized control of all functions means that a PhaseCam Twyman-Green can be operated remotely in measurement towers, vacuum chambers, environmental chambers and other challenging locations.

No Calibration Required

With no mechanical phase-shifting as in a temporal interferometers, fewer parts, and no delicate high-voltage PZT actuators, a Twyman-Green PhaseCam is always accurate.

High Resolution

The inherently on-axis design of the Twyman-Green interferometer means high resolution and accuracy is built into PhaseCams.

Measure Low Return Systems or Highly Reflective Surfaces

Polarization control lets you match the energy in the test and reference beam to optimize fringe contrast. This feature lets you significantly improve the measurement noise floor and vertical resolution. A wide range of test setup reflectivities can be supported, and excellent contrast can be achieved, even in low return setups.