An apparatus for performing nucleic acid amplification reactions includes a thermally-conductive receptacle holder with multiple receptacle wells. Each well has a through-hole extending from an inner surface of the well to an outer surface of the holder. A cover is rotatable between an open position and a closed position relative to the holder and is configured to exert a force onto any receptacles in the wells when the cover is in the closed position. The apparatus includes multiple optical fibers, and each of the optical fibers provides optical communication between one of the wells and an excitation signal source and/or an emission signal detector. A thermal element is positioned between a thermally-conductive support and the receptacle holder.