Optical system for auroral diagnostics package onboard PoGO-Lite astrophysical balloon

Abstract: This thesis report describes the development of the optical system ALBERT (Alfvén Laboratory Baloon ExpeRimenT) that will fly from ESRange in 2011 as an auroral diagnostic unit for the PoGO-Lite mission. ALBERT has been developed at KTH in collaboration with the University of Southampton. ALBERT consists of two main systems. A support structure (mechanical system) and two spectrometers (optical system). The development started with a conceptual CAD assembly and the end objective was to have ALBERT manufactured. The mechanical system has been developed and manufactured in house and the parts are mainly manufactured from aluminum. The mechanical system was codeveloped with the thermal engineer to make sure the etalon temperature would be kept at a stable 20°C to ensure the performance of the spectrometers. The thesis also aimed to optimize the photometers for the use in the PoGO-Lite mission. The photometers have been designed to detect auroral oxygen emissions at´777.4nm and 844.6nm. The photometers consist of one interference filter, one Fabry-Pérot Etalon filter, two lenses, an aperture and one photomultiplier tube. The Fabry-Pérot Etalon filter is mounted on a tilting mechanism which enables the photometer to become a spectrometer. Extensive testing has been performed throughout this project with the objective to optimize the spectrometers. Knowhow about the system and its components enables the design of the aperture, a critical component that determines the performance of the´spectrometer. After extensive testing of the Fabry-Pérot Etalon filters and the interference filters with an Michelson interferometry spectrometer a final characterization of the Fabry-Pérot Etalon could be done using an Argon lamp and a high-end EMCCD camera. It could then be concluded that one of the etalons was not to specification and was rendered useless for ALBERT. The other etalon could be used and the optimization of the aperture for that spectrometer concluded in that a banana shaped aperture was the optimal. The inner and outer radii of the aperture corresponded to the radii of the rings from the interesting spectrum in the characteristic ring pattern produced by an etalon.