Thermal management of film deposition processes. In one aspect, a deposition system includes a vacuum chamber defining an evacuated interior volume, a deposition source disposed within the interior volume, a substrate holder disposed within the interior volume and arranged to hold a substrate with a first surface of the substrate facing the deposition source and a second surface of the substrate disposed facing away from the deposition source, and a heat sink disposed to have a first side of the heat sink in radiative thermal contact with the second surface of the substrate held by the substrate holder, the first side of the heat sink comprising a collection of features having a longitudinal dimension that is four or more times larger than a lateral dimension between the features, the features thereby dimensioned and aligned to reflect, multiple times in succession, radiative thermal emissions of the second surface of the substrate.