Image degradation due to scattered radiation from residual optical fabrication errors is a serious problem in many optical systems operating at short wavelengths or for some optical fabrication processes. Most currently-available image analysis codes (ZEMAX, ASAP, FRED, etc.) require the scatter behavior (BRDF data) as input in order to calculate the image quality from such systems. This BRDF data is difficult to measure and rarely available for the operational wavelengths of interest. An FFTLog algorithm enables the practical use of the computationally intensive Generalized Harvey-Shack (GHS) surface scatter theory to calculate BRDFs (from assumed or measured surface metrology data) for increasingly short wavelengths that violate the smooth surface approximation implicit in the Rayleigh-Rice surface scatter theory. Surface roughness must be specified (and measured) over the entire range of relevant spatial frequencies. Commercially-available optical analysis codes can then utilize these predicted BRDFs to make accurate image quality predictions. The GHS surface scatter theory can thus be used to specify optical fabrication tolerances necessary to satisfy specific image quality requirements in the design phase of a program (using assumed surface PSDs), and then be used (with measured metrology data) during the optical fabrication process to determine when the surfaces are smooth enough to satisfy the top-level image quality requirements.
9/17/2013 Special Seminar: Specifying Optical Fabrication Tolerances to Meet Specific Image Quality Reguirements
Published on May 24, 2013
Speaker:James E. Harvey (Photon Engineering, LLC)