Aspheric surfaces are indispensable in high-performance optical systems. The ability to accurately manufacture these surfaces to the required shape depends on the ability to measure them. In this project we develop and characterize procedures that address this measurement challenge through the application of Computer Generated Holograms (CGHs). The project focuses on an innovative application of CGHs to measure the mandrels used to form mirrors for X-ray telescopes.
The project addresses metrology needs of U.S. industry and other agencies for the manufacture and application of ultra-precision surfaces and optical elements possessing high added-value. Ultra-precision surfaces and optical elements are essential to product innovations in many high-tech areas, such as semiconductor manufacturing, medical technology, defense, homeland security, consumer products, office automation, information technology, and science. Product examples range from an enormous variety of imaging systems to hard-drive platters, automotive lighting, laser beam shapers, and x-ray focusing optics. Advanced optical elements boost competitiveness and technological leadership in a broad range of manufacturing sectors. “Light is the tool of the future”, as evidenced by the growth in optical inspection, machine vision, and laser systems for welding and additive manufacturing. Advances in nano-scale and semiconductor manufacturing fundamentally rely on advances in ultra-precision surfaces and high-performance optical elements, such wafers, photomasks, and the lenses and mirrors used in optical projection lithography.
Both the manufacture and development of ultra-precision surfaces and optical elements critically depends on the ability to measure their performance. Despite advances in deterministic manufacturing techniques, only optical surfaces that can be measured can be made. This is particularly important for imaging systems performing at the limit imposed by the wave nature of light (“diffraction limit”), be they very large optical telescopes with apertures of many meters, or small cameras in mobile phones which must achieve good imaging performance in a tiny space.
Advanced optical elements incorporate features that yield vastly improved performance but pose significant measurement challenges. Examples of such features are complex surfaces, i.e., surfaces that are neither flat nor spherical, micro- and nano-scale surface structures, extreme accuracies, special materials and coatings, and adaptive technologies. The development and manufacture of these advanced features depend strongly on advances in traceable metrology for optical figure and wavefront. In high-impact applications, such as semiconductor lithography, the required form accuracies are at the (sub-) nanometer level. Traceability requires standards-compliant uncertainty statements that are often difficult to develop, but are increasingly demanded for ISO-certified quality systems and export. No general, widely-recognized, validated way exists to calibrate complex and nano-structured (optical) surfaces, and the application range and uncertainty of existing methods are poorly understood. This is a persistent measurement barrier to the widespread manufacture and adoption of these elements, despite their high potential for product innovations.
The project addresses these measurement challenges through the following objectives:
Figure 1. Form error of a 1 kg silicon sphere. The form error was obtained from 138 overlapping images.
Lead Organizational Unit:pml
Related Programs and Projects:
Physical Measurement Laboratory (PML)