Using Zemax programming language and API as a method to perform parametric ghost analysis, chromatic aberrations, and baffle thermal loading on the LiteBIRD medium and high frequency telescopes

We combine use of the Zemax Programming Language and an API (Application Programme Interface) feature in the Zemax Opticstudio software which allows for rapid ray-tracing computations and maps of intermediate ray distribution intersections with in-house IDL code to produce maps of stray-light distribution and spectral content of ghost images. The calculation of the spectral amplitude of the latter is performed via prior knowledge of spectral transmission of all optical elements involved in a refractor telescope. The results are of generic nature and can be applied to any optical system. For the numerical examples in this case we consider the JAXA LiteBIRD CMB Medium and High frequency telescopes as a study case and perform a parametric study of the position of its infrared rejecting filters by looking at multiple configurations within a python envelope. By manipulating the resulting intermediate products of ray incidence distribution we determine the optimal position of the filters that will minimize ghost features on the focal plane (or define some competing configurations based on desired outcomes).The resulting analysis is in competition with other aspects of filter positioning (mechanical and thermal) so the results of this optimization is not necessarily a final outcome. Results from such a study can be used to characterize the variation of spectral response across the focal plane caused by the impact angle distribution on the optical coatings and finally the distribution of thermal (out of band) rejected light reflected by the filters on the optical baffles. The first can be obtained with the majority of optical modelling commercial packages, the second are more complex and can also be done in a similar way with packages that perform non-sequential analysis.