Ideally, the response of the Advanced Topographic Laser Altimeter System (ATLAS) instrument on the Ice, Cloud, and land Elevation Satellite–2 (ICESat-2) observatory to returns from a flat target at a fixed distance would be a single peak. However, ICESat-2 profiles from very flat surfaces display extra features below the presumed Earth surface. This paper identifies the multiple reflections within the ATLAS receiver that create those extra pulses. We describe their sources, compare their measured position to optical ray trace predictions, and discuss their relative amplitude. We then explore the possibility of using afterpulses to extract surface elevation information from highly saturated returns, in which the first return pulse is distorted and displaced by nonlinear effects in the detector.