Absolute Metrology Services

A Woman-Owned Business

Absolute Metrology Services has extensive experience with interferometry and optical testing. Over the past 20 years we have worked with large aperture interferometers and interferometric microscopes, from basic and advanced interferometry training levels to high-level, absolute reference certifications and calibrations. Browse our offerings on this site, or contact AMS directly with your specific needs.

Reference Certifications and Calibrations

When your reference optics are properly certified, you know the level of uncertainty that the reference optic surface error is introducing into each measurement. When your reference optics are properly calibrated, these errors can be subtracted from your measurements. This is critical when the quality of test part approaches that of the transmission flat or sphere used to test it. Interferometers should have their Transmission Flats (TFs) and Transmission Spheres (TSs) certified regularly to ensure their form is still within their original stated specification. AMS can perform reference certifications and calibrations on Fizeau-style transmission spheres and transmission flats if they are compatible with a 4" or smaller Zygo bayonet mount. Contact AMS if you have a piece that does not fit these requirements.

All of the tests described below are ISO 17025:2005 compliant. They either produce a reference directly from a self-referencing, absolute test procedure or are directly traceable to a reference measured this way.

Certification of Transmission Flats, Reference Flats, and General Flat Optics

This test is a single cavity test comparing your flat optic to a previously calibrated "master" TF or RF which has been calibrated using the Absolute Flat Test (below) and its errors properly registered and subtracted from the certification measurement. It provides adequate traceability to meet the requirements of ISO 17025:2005.

Certification of Transmission Spheres, Reference Spheres, and General Spherical Optics

This certification will test your part directly using the Absolute Spherical test (below) or test your part against a "master" spherical surface calibrated using the Absolute Spherical Test with its errors property registered and subtracted. It provides adequate traceability to meet the requirements of ISO 17025:2005.

Absolute Flat Test

This test is an extension of the standard three-flat test which yields a full-area map of the flat under test. It provides adequate traceability to meet the requirements of ISO 17025:2005.

Absolute Spherical Test

This test yields the full area data over a spherical surface, using a combination of rotational measurements and measurements at 'cats-eye' positions. It provides adequate traceability to meet the requirements of ISO 17025:2005.

Contact AMS to discuss your reference calibration needs.

On-Site Reference Certification / Calibration for Large Aperture Transmission Flats, 12" and Up

If you have a large aperture interferometer of your own, and it is time to have your references certified or calibrated, consider on-site reference calibration. AMS strongly recommends using this method to calibrate large flats that would otherwise have to be removed from their cells for shipping. Why? When a reference is calibrated, removed from its cell, and replaced at your site, it will always have a different shape than its original calibration result. Additional advantages of on-site calibration include:

  • Shorter downtime, since reference does not need to ship and "wait in line" for calibration
  • Less handling means reduced risk to the optic
  • Analysis of error sources and calibration uncertainty is performed from your site data

AMS can work around your schedule to perform reference calibrations in your optical testing laboratory without ever removing the reference from its cell. Use on-site calibration to achieve the lowest uncertainty in your measurements of large pieces.

Most large aperture Fizeau interferometers have the capability to measure to better than 1/100th wave uncertainty after calibration and error subtraction is implemented. The quality of these absolute measurements depends mostly upon proper environmental control and good metrology practice. AMS will take care of the good metrology practice, and will work with you to analyze your cavity environment before any calibration is performed.

Contact AMS to discuss your on-site reference certification and calibration needs.


Our Services

Interferometry Training

Reference Calibration

Applications Engineering

Optical Testing Services


AMS is a subsidiary of Greywall Incorporated
East Hampton, CT 06424
ph: 860-883-9953
alt: 860-267-6177
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