Transmitted Wavefront Error of Finite Conjugate Lenses
Measuring the transmitted wavefront error (TWE) of singlets, doublets, triplets, achromatic lenses, and compound lenses with diffractive or aspheric surfaces, is typically completed with a laser interferometer. The diagram below shows a typical setup using a Fizeau Interferometer, though testing can also be completed with a Twyman-Green interferometer.
Measuring TWE with a Fizeau Interferometer
Typical setup for measuring the transmitted wavefront error of a finite conjugate lens.
An interferometer with a HeNe laser source can often be used to measure surface quality. However, depending on the optical coatings and/or the application, it may be important to test TWE using an interferometer with a laser source close to the optic’s functional wavelength.
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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 AccuFiz interferometers feature optional Dynamic Interferometry®, which enables all measurement data to be acquired simultaneously. Vibration is no longer an issue, and an isolation table is not needed.
Transmission Sphere Selection Guide
Learn how to choose the correct transmission sphere for your application.
Measuring TWE with a Twyman-Green Interferometer
A Twyman-Green interferometer can also be used to measure TWE of a finite conjugate lens. A beam expander can be used to increase the size of the measurement beam.
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