An apparatus for performing nucleic acid amplification reactions, the apparatus comprising: a thermally-conductive receptacle holder, the receptacle holder comprising a plurality of receptacle wells, each of the receptacle wells being configured to receive a receptacle, and each of the receptacle wells having a through-hole extending from an inner surface of the receptacle well to an outer surface of the receptacle holder; a thermally-conductive support, the support being a solid member comprising a base portion and an upright portion, wherein the base portion comprises a plurality of through-holes, and wherein each of the through-holes of the base portion is in alignment with a corresponding one of the through-holes of the receptacle holder; a thermal element positioned between a first side of the upright portion of the support and an opposed side surface of the receptacle holder; a compressive housing having a top surface positioned above the receptacle holder, the top surface having a plurality of through-holes, each of the through-holes of the compressive housing being in alignment with a corresponding one of the receptacle wells; a cross-brace mounted to the first side of the upright portion of the support, wherein the cross-brace exerts a force onto a side surface of the compressive housing such that the compressive housing exerts a force onto the receptacle holder; and a plurality of optical fibers, each of the optical fibers providing optical communication between one of the receptacle wells and at least one of an excitation signal source and an emission signal detector, wherein a first end of each of the optical fibers is disposed outside, within, or extends through the through-hole of a corresponding one of the receptacle wells, and wherein a second end of each optical fiber is in optical communication with the excitation signal source and/or the emission signal detector. a thermally-conductive receptacle holder, the receptacle holder comprising a plurality of receptacle wells, each of the receptacle wells being configured to receive a receptacle, and each of the receptacle wells having a through-hole extending from an inner surface of the receptacle well to an outer surface of the receptacle holder; a thermally-conductive support, the support being a solid member comprising a base portion and an upright portion, wherein the base portion comprises a plurality of through-holes, and wherein each of the through-holes of the base portion is in alignment with a corresponding one of the through-holes of the receptacle holder; a thermal element positioned between a first side of the upright portion of the support and an opposed side surface of the receptacle holder; a compressive housing having a top surface positioned above the receptacle holder, the top surface having a plurality of through-holes, each of the through-holes of the compressive housing being in alignment with a corresponding one of the receptacle wells; a cross-brace mounted to the first side of the upright portion of the support, wherein the cross-brace exerts a force onto a side surface of the compressive housing such that the compressive housing exerts a force onto the receptacle holder; and a plurality of optical fibers, each of the optical fibers providing optical communication between one of the receptacle wells and at least one of an excitation signal source and an emission signal detector, wherein a first end of each of the optical fibers is disposed outside, within, or extends through the through-hole of a corresponding one of the receptacle wells, and wherein a second end of each optical fiber is in optical communication with the excitation signal source and/or the emission signal detector.