<title>Computer modeling of slit diffraction (spatial filtering)</title>

Abstract

Generally, there are two sources of diffraction to consider when modeling optical systems: diffraction due to apertures (edge diffraction) and slit diffraction (spatial filtering). Most optical design and analysis programs can handle aperture diffraction, but until recently, none could easily handle slit diffraction. This type of analysis is needed in many areas of optical instrumentation such as spectroscopy or laser systems that utilize spatial filtering. In order to compute slit diffraction, an incoming optical field must first be truncated by a very small aperture (slit, pinhole, etc.). A Fourier decomposition is then performed on this truncated field to produce new direction vectors that then become the diffracted field. At the request of Ball Aerospace Systems group (BASG), Breault Research Organization (BRO), Inc. has developed a new subroutine called DECOMPOSE for their Advanced Systems Analysis Package (ASAP) software. This paper will describe how BASG verified the performance of this subroutine and evaluated it against textbook theory to prove its viability. This work was performed in an effort to analyze a portion of the Infrared Spectrograph (IRS) for the Space Infrared Telescope Facility (SIRTF).