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Transmitted Wavefront Error of an Infinite Conjugate System

Optical Setups


Measuring the transmitted wavefront error (TWE) of imaging, zoom, and camera lenses, multi-element lens assemblies, image relays, microscope objectives, and refractive telescope objectives is typically completed with a laser interferometer. The diagram below shows a typical setup using a Twyman-Green Interferometer, though testing can also be completed with a Fizeau interferometer.


Measuring TWE with a Twyman-Green Interferometer

infinite conjugate system, transmitted wavefront error, optical setups, twyman-green interferometer

Standard setup for measuring the transmitted wavefront error of an infinite conjugate system.

Depending on the application, it may be important to test TWE using an interferometer with a laser source close to the optic’s functional wavelength. PhaseCam interferometers are available in a range of visible and IR wavelengths.

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

Required Equipment

The diagram below shows the equipment needed to measure an infinite conjugate system with an PhaseCam Twyman-Green interferometer.
infinite conjugate system, transmitted wavefront error, optical setups, twyman-green interferometer
Required Components
Twyman-Green Interferometer More Information
Diverging Optic Specifications
5-Axis Stand Specifications
Dovetail Mount Specifications
Bayonet, 3-Jaw, or Shelf Mount Specifications
2-Axis base with Tip/Tilt Specifications
Return Flat Specifications


Other Considerations

Low Return Systems

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 system reflectivities can be supported, and excellent contrast can be achieved, even in low return systems.

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.

4D PhaseCam Twyman-Green interferometers feature Dynamic Interferometry®, which enables measurement data to be acquired simultaneously. Because acquisition speed is so fast, vibration is no longer an issue, and an isolation table is not needed.


Measuring TWE with a Fizeau Interferometer

A Fizeau interferometer, which is commonly available in an optical shop, can also be used to measure TWE of an infinite conjugate lens.

Need Assistance with Measuring Transmitted Wavefront Error?

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