Optical modeling of finite element surface displacements using commercial software

Abstract

Keith B. Doyle, Victor L. Genberg, Gregory J. Michels, Gary R. Bisson Sigmadyne, Inc. 803 West Avenue, Rochester, NY 14611 ABSTRACT The accuracy of optical modeling techniques to represent finite element derived surface displacements is evaluated using commercial software tools. Optical modeling methods compared include the Zernike polynomial surface definition, surface interferogram files, and uniform arrays of da ta in representing optical surface errors. Methods to create surface normal displacements and sag displacements from FEA displacement data are compared. Optical performance evaluations are performed as a function of surface curvature ( f/#). Advantages and disadvantages of each approach are discussed. Keywords: opto-mechanical analysis, integrated modeling, optical surface displacements, interferogram files, finite element analysis 1. INTRODUCTION Predicting optical performance over the operational environment of an optical system often requires importing finite element computed surface displacements into the optical model. This may include predicting surface deformations in service environments due to inertial and thermal loads to on-orbit random vibrations to predicting performance of an adaptive optical system. In general, for each of the above mechanical analyses, the modeling process first requires computing the mechanical displacements of the optical surface using finite element analysis, second post-processing the FEA displacement data into the appropriate optical displacement value, and third, repr esenting the surface errors in the optical model using various optical modeling methods. Common optical modeling methods used to represent surf ace errors in commercially available optical design software such as CODEV