Adaptive interferometric metrology for testing complex, rotationally variant optical surfaces like freeform mirrors
Institute Reference: 2-18037
Background
Traditional metrology techniques for optical surfaces such as spherical and flat optics typically use full-field interferometry, but they struggle to measure complex, rotationally variant surfaces like toroids or freeform mirrors. These surfaces have unique geometries that create high interference fringe density, which conventional sensors cannot adequately resolve. Current methods, such as using computer-generated holograms (CGHs) or deformable mirrors, are often limited by high costs, the need for unique components for each surface type, and poor adaptability during manufacturing.
Technology Overview
This invention introduces a novel metrology system for testing optical surfaces with rotational variance, such as toroidal and freeform surfaces, using a high-definition, phase-only liquid crystal spatial light modulator (SLM). The SLM acts as a reconfigurable null element, enabling real-time adaptation of the phase function to compensate for surface deviations. By using a simulated nulling phase function encoded onto the SLM, it generates a null interferogram capable of measuring complex surfaces without the need for custom mechanical optics or tilting the optic under test.
The system uses phase wrapping techniques to effectively null large surface sags by encoding the phase function in multiples of 2π radians, thus removing the theoretical upper limit on surface sag. The SLM enables both in-situ measurements during the manufacturing process and final quality checks, offering high flexibility compared to static null optics.
Benefits
This metrology system offers significant advantages, beginning with its adaptable testing capabilities. It allows for single-shot, adaptive measurements across a wide range of optical surfaces without requiring unique optical components for each specific type, greatly simplifying the testing process. Cost efficiency is another major benefit, as it eliminates the need for expensive computer-generated holograms (CGHs) and custom-designed null optics, thereby substantially reducing overall metrology expenses.
The system also delivers high precision, capable of handling high sag deviations and complex asymmetries. Thanks to the high-definition spatial light modulator and phase wrapping techniques, it can measure these deviations without any theoretical upper limits on sag. Furthermore, its in-situ capability enables testing during multiple stages of the manufacturing process. This feature allows for immediate adjustments, minimizing the need for corrections after production is complete and improving overall efficiency in manufacturing high-precision optical components.
Applications
This technology is particularly well-suited for the quality assessment of optical surfaces, especially those with complex geometries, like those found in advanced telescopes, medical imaging devices, and defense optical systems. It excels at evaluating surfaces that are challenging to measure using conventional techniques, ensuring that they meet high precision standards.
Moreover, the system can be seamlessly integrated into the manufacturing process, allowing for real-time quality control and adjustments. This integration significantly enhances the efficiency of producing high-precision optical components, as it facilitates early detection and correction of errors during production, reducing waste and improving overall quality outcomes.
Opportunity
The University of Rochester is open to exploring funded research collaborations, licensing agreements, and other partnership opportunities.