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CGH Nulls

With our CGH Nulls, you can test aspheres using your existing interferometer. The CGH Null transforms the spherical or collimated test beam into the aspheric wavefront required to produce a null interferogram. Our CGH Positioners and Alignment CGHs simplify the alignment of CGH to interferometer.

CGH Null Test of Custom Asphere

Easy to Use

Mount CGH Positioner with Alignment CGH in your interferometer’s test beam.
Adjust decenter (or tilt-tip) and focus to acquire and null alignment fringes.
Remove Alignment CGH and replace with Custom CGH Null.
Align test optic to acquire and null fringe pattern. Record interferogram.

Breaking the Rules

Convention says that a CGH null should be used in single pass because of low diffraction efficiency. It should be located in a collimated beam to ease alignment tolerances. Test and reference beams should pass similarly through the CGH to cancel any substrate aberrations.

Our CGH Nulls typically violate these rules, so we must produce high efficiency CGHs on precision substrates and align them to micron tolerances. You benefit in simple test configurations that use your existing interferometer and accessories.

CGH transmitted wavefront error


Our CGH nulls are encoded to meet your accuracy requirements. Errors due to as-built substrate thickness, zero-order transmitted wavefront distortion and flatness are incorporated into a software null that should be subtracted from your measured interferograms for best accuracy.

System errors of your interferometer and transmission sphere can be compensated in the usual manner—by measuring a good spherical surface and subtracting the result from subsequent interferograms.

Full Documentation

Diffraction International delivers complete technical documentation with each and every CGH null. The report is fully electronic and can navigated with any current web browser. View a sample report from a recent H95F3C Cylinder Null.

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Page updated: 8 November 2018

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