A slot impingement cooler is formed of a plurality of sets of foils in a stacked and registered array. In each set of foils, a first foil has supply slots that direct a flow of coolant, a second foil has a plurality of effective light-trap cavities, a third foil has return slots that return the flow of coolant, and an optional fourth foil has a plurality of effective light-trap cavities. The foils have registered supply manifold openings and registered return manifold openings therethrough.