Hybrid compensation method for testing large-aperture low-sag freeform mirrors
Optics Express
|August 14, 2026
Summary
This study introduces a hybrid method using computer-generated holograms and a spherical mirror to test large, complex freeform mirrors. The novel approach achieves high-precision measurements for large-aperture, low-sag surfaces.
Area of Science:
- Optical Engineering
- Metrology
- Surface Testing
Background:
- Computer-generated holograms (CGH) are precise for surface testing but limited by equipment aperture constraints.
- Measuring large-aperture, high-precision freeform mirrors is challenging due to these limitations.
Purpose of the Study:
- To develop a hybrid compensation method for testing large-aperture, low-sag freeform mirrors.
- To overcome the aperture constraints of traditional CGH testing.
Main Methods:
- A hybrid approach combining CGH with a spherical mirror.
- Development of a hybrid computational method using a virtual equivalent surface to calculate CGH phase function.
- Establishment of an interferometric data-processing model including distortion correction and error removal.
Main Results:
- Experimental validation on a large-aperture freeform mirror (698 mm × 210 mm).
- Achieved low-frequency measurement accuracy of 3.6 nm RMS.
- Achieved clear aperture surface measurement accuracy of 8.3 nm RMS.
Conclusions:
- The hybrid compensation method enables high-precision testing of large-aperture, low-sag freeform surfaces.
- The spherical mirror compensator shows general applicability for advanced optical metrology.
