A Method to Retrieve the Total Flux at Lyman-Alpha in Micro-Channel-Plate Detectors Affected by Gain Sag: Application to the LAMP UV Imaging Spectrograph Onboard the Lunar Reconnaissance Orbiter

Micro-Channel Plate (MCP) detectors can suffer from a form of degradation known as gain sag in regions with significant fluence. We have developed a method to recover the total Lyman-Alpha (Ly-[Formula: see text]) emission line (121.6[Formula: see text]nm) flux for the Lyman-Alpha Mapping Project (LAMP) UV imaging spectrograph onboard of the Lunar Reconnaissance Orbiter (LRO), where gain sag issues are important. The constant ratio between the Ly-[Formula: see text] emission line and its ghost image at shorter wavelengths allows for a useful correction factor for the true flux at the Ly-[Formula: see text] region of the detector. A similar method could be used in other spectrographs whenever a ghost image of sufficient brightness is present.