OPTICAL-PERFORMANCE OF HIGH-ASPECT LIGA GRATINGS II

The analysis of an IR tunable filter that uses a transmission grating with variable spacing is extended to include incident spherical waves instead of plane waves and to illustrate specifically the effects of f inite conductivity in the metal. The model is based on a rigorous vect or solution of Maxwell's equations implemented in a finite elements so lver. The modeling results based on tabulated optical properties of ni ckel are compared with experimental measurements made with filters fab ricated in permalloy by the lithographie, galvanoformung, abformung (L IGA) process. The theoretical and experimental results compare quite w ell and suggest that the resolution of the filter is severely reduced at the shorter wavelengths (less than 4 mu m). At longer wavelengths, the resolution is limited by the aspect ratio of the LIGA structures. A spectral resolution of 0.1 mu m appears to be practical. (C) 1998 So ciety of Photo-Optical Instrumentation Engineers. [S0091-3286(98)01311 -7].