Figuring large optics at the sub-nanometer level: compensation for coating and gravity distortions

Area of Science:

• Optical engineering
• Materials science
• Metrology

Background:

• Modern manufacturing enables sub-nanometer surface precision for large optics.
• Coating deposition and gravitational forces cause significant deformations.
• Existing compensation methods have limitations for large optical components.

Purpose of the Study:

• To demonstrate and model a method for compensating coating-induced stress in large optics.
• To achieve sub-nanometer surface accuracy (λ/200) on a 370mm substrate.
• To identify key factors and limitations for fabricating large, precision optics.

Main Methods:

• A novel process involving coating and annealing was applied to a 370mm substrate.
• Finite element analysis and optical modeling were used to simulate the stress compensation process.
• Surface figure measurements were performed to verify the achieved precision.

Main Results:

• Coating stress on a 370mm substrate was successfully compensated to λ/200 using the coating and annealing process.
• Modeling identified critical factors influencing the effectiveness of stress compensation.
• The study quantified the limitations of using coatings for deformation compensation.

Conclusions:

• The demonstrated coating and annealing process is effective for compensating stress in large optics.
• Incorporating stress effects into optical design is crucial for future high-precision applications.
• Understanding coating-substrate interactions is vital for advancing gravitational wave detection and other precision optical technologies.