Abstract: A reaction chamber for a controlled reaction on a reaction surface of a sample provides for controlled distribution of radiant energy over the reaction surface to offset radiant heat loss of the sample, and establishes uniform distribution of reactant flow on the sample. A lamp housing supplies radiant energy over the sample, which absorbs at least a component of the radiant energy. A support member which supports the sample within the reaction chamber is formed of a material which is essentially transparent to the radiant energy so that it does not behave as a susceptor. An array of lamps, is mounted with the reaction chamber so that direct radiant energy is transmitted through a window to the reaction surface of the sample. A reflecting surface on the housing includes a lamp seat for each lamp in the array with an individually specified position, curvature and tilt with respect to the reaction surface.