A small FORTRAN program for assessment of alignment tolerance in arbitrary sequences of flat or conic section mirrors

This report is a new edition of [1] with different title, the limitation to flat mirrors having been removed in the new version of the program (available in source code alongside this report). All types of commonly used mirrors are now included, i.e. flat and elliptic, hyperbolic, parabolic. Spherical mirrors are only a special case of elliptic ones. This revised 2022 edition introduces support for multi-beam quasi-optical transmission lines and an estimation of ohmic loss. Mirrors are a common component in THz and sub-THz quasi-optical systems. The system designer always faces the need to specify alignment tolerances for manufacturing, but computing the impact of misalignments using commercial programs can be tedious, requiring lots of simulations. This program tries to alleviate the burden by performing a Montecarlo analysis for an arbitrary sequence of mirrors, specified with the positions of the central axis reflection points in a single reference frame. It is somewhat similar to [2]. The first point in the sequence must be the position of the source, the last an arbitrary point along the axis of the output beam. Source and mirrors are assumed to have random errors in orientation, with a uniform distribution function within the specified tolerance. In order to support multi-beam transmission lines, the perturbation in mirror orientation can be applied on a specified point (e.g. mechanical center of mirror), so that results are consistent across beams. The program also computes the polarization and its dependence on alignment tolerances. To aid designers in choosing the optimum polarization, ohmic loss is also computed, taking into account its polarization dependency. It is freeware and available in Fortran 95 source form at ISTP (former IFP) website alongside this report. Users are kindly requested to cite this report in their papers.