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. <EOS>