Robustly Designed Optical Coatings for Cutting-Edge Science

Brian Bauman | 23-FS-024

Project Overview

Our goal is to create exquisite science-enabling optical coatings by designing them to be robust to common manufacturing errors in thickness and refractive index, thus opening new instrument design opportunities with reduced risk. We aim to achieve performance not through conventional tightening of coating tolerances, but by novel design of coatings to be more tolerant of errors in the first place -- achieving improved as-built performance. The key to the approach is a mathematical theory that analytically predicts the effects of tolerances and compensators so that those effects can be accurately included in the design merit function; this approach was successfully used in optical design to create systems tolerant of alignment errors. We applied a similar approach to thin film design. To demonstrate feasibility, we needed to show that we can create an appropriate coating performance perturbation theory that analytically calculates the performance degradation due to errors in layer thicknesses and refractive index. We also developed science cases that showed the scientific benefit of building out a capability to robustly-design optical coatings.

This study has shown that it is feasible to robustly-design optical coatings, and it has been somewhat less difficult than expected. We have obtained an analytic solution to performance degradation due to tolerances. Most components of the analytic solution are simple calculations based on information already calculated during optimization. A couple components are somewhat more complex, and we hope to find a simpler solution with a little more effort. Even so, we predict the additional computation time will be acceptable within the optimization loop. We have found that the "stock" scripting capabilities within a particular thin-film design code should be sufficient for implementing our approach within the optimization loop.

Mission Impact

Demanding and robust optical systems are enabling for a cross-cutting range of applications in astronomy, remote sensing, laser systems, and national security. This project supports Lawrence Livermore National Laboratory's Core Competencies of Lasers and Optical Science and Technology and Advanced Manufacturing, as well as the Director's Initiative in the areas of Optics and Manufacturing Technologies and Space Science and Security. Combined with building out a robust coating design capability, we expect to fundamentally change how the thin-film co mmunity designs coatings by developing the theory to optimally design exquisite coatings for manufacture. We also will enable new, previously unobtainable science with more ambitious (yet more realistic) coating specifications.