RLS iOH: ExoMars Raman laser spectrometer optical head bread board to flight model design and performance evolutions

Abstract

Raman Laser Spectrometer (RLS) is the Pasteur Payload instrument of the ExoMars mission that will perform Raman spectroscopy for the first time in a planetary space mission. RLS main units are: SPU (SPectrometer Unit), iOH (internal Optical Head), and ICEU (Instrument Control and Excitation Unit), that includes the laser for samples excitation purposes. The iOH focuses the excitation laser into the crushed samples (located at the ALD, Analytical Laboratory Drawer, carrousel) through the excitation path, and collects the Raman emission from the sample (collection path). Its original design presented a high laser trace reaching to the SPU detector, and although a certain level was required for instrument calibration, the found level was expected to be capable of degrading the acquired spectra confounding some Raman peaks. So, the iOH optical and opto-mechanical designs were needed to be updated from the BB (Bread Board) to the engineering and qualification model (iOH EQM), in order to fix the desired amount of laser trace, and after the fabrication and the commitment of the commercial elements, the assembly and integration verification (AIV) process was carried out. Considering the results obtained during the EQM integration verification and the first functional tests, the RLS calibration target (CT) emission analysis, additional changes were found to be required for the Flight Model, FM. In this paper, the RLS iOH designs and functional tests evolutions for the different models are summarized, focusing on the iOH AIV process and emphasizing on the iOH performance evaluation (by using CT spectra) from the re-design activities.