Stray light compensation for dust analysers based on light scattering

摘要

One of the key issues concerning the measurement of size and density of dust grains based on light scattering system is the compensation of the stray light due to the optical components misalignment and to the possible contamination of these components by the dust particles during the measurement runs. This paper focuses on the case study of MEDUSA ( Martian Environmental DUst Systematic Analyzer), one of the experiments initially selected for the ExoMars mission,planned by the European Space Agency (ESA), with the scientific objective to study water and dust in Mars atmosphere.The MEDUSA experiment foresees an Optical System (OS) aimed at measuring atmospheric dust content and size distribution. One pump assures that the proper gas and dust flow circulates inside the instrument. This paper reports the description and trade off analysis of several techniques for the stray-light compensation implemented on the MEDUSA OS Proximity Electronics (PE) Test Board (2006), designed and manufactured by INAF-Osservatorio Astronomico di Capodimonte, in the frame of the MEDUSA Bread Board (B/B) activities. The PE Test Board can implement more than one compensation mode, such as: AC coupling, DC coupling with offset compensation via external loop and DC coupling with offset compensation via on board HW loop. The choice among the mentioned compensation modes shall be done also according to the configuration of the overall acquisition system, implemented by the Main Electronics (ME), as explained in the reported trade-off analysis. For the architecture configuration of the industrial breadboard (2008) the preferred solution was the one based on the DC coupling with on board HW loop, for which some test results are reported.