A system for creating a feedstock line for additive manufacturing of an object , the feedstock line having a feedstock-line length, the system comprising: a filament supply , configured to dispense a precursor tow , comprising elongate filaments ; a filament separator , configured to separate the precursor tow , dispensed from the filament supply , into individual ones of the elongate filaments or into subsets of the elongate filaments , wherein each of the subsets comprises a plurality of the elongate filaments ; an optical-direction-modifier supply , configured to dispense optical direction modifiers to be applied to the individual ones of the elongate filaments or the subsets of the elongate filaments , originating from the filament separator , wherein each of the optical direction modifiers has an outer surface , and each of the optical direction modifiers is configured such that when electromagnetic radiation strikes the outer surface from a first direction, at least a portion of the electromagnetic radiation departs the outer surface in a second direction that is at an angle to the first direction; a combiner , configured to combine the individual ones of the elongate filaments and the optical direction modifiers , dispensed by the optical-direction-modifier supply , or the subsets of the elongate filaments and the optical direction modifiers , dispensed by the optical-direction-modifier supply , into a derivative tow so that the optical direction modifiers are interspersed among the elongate filaments ; and a resin supply , configured to provide a resin to be applied to at least one of the precursor tow dispensed from the filament supply , the individual ones of the elongate filaments or the subsets of the elongate filaments , originating from the filament separator , the optical direction modifiers , dispensed from the optical-direction-modifier supply , or the derivative tow , originating from the combiner , such that the elongate filaments and the optical direction modifiers in the derivative tow are covered with the resin . a filament supply , configured to dispense a precursor tow , comprising elongate filaments ; a filament separator , configured to separate the precursor tow , dispensed from the filament supply , into individual ones of the elongate filaments or into subsets of the elongate filaments , wherein each of the subsets comprises a plurality of the elongate filaments ; an optical-direction-modifier supply , configured to dispense optical direction modifiers to be applied to the individual ones of the elongate filaments or the subsets of the elongate filaments , originating from the filament separator , wherein each of the optical direction modifiers has an outer surface , and each of the optical direction modifiers is configured such that when electromagnetic radiation strikes the outer surface from a first direction, at least a portion of the electromagnetic radiation departs the outer surface in a second direction that is at an angle to the first direction; a combiner , configured to combine the individual ones of the elongate filaments and the optical direction modifiers , dispensed by the optical-direction-modifier supply , or the subsets of the elongate filaments and the optical direction modifiers , dispensed by the optical-direction-modifier supply , into a derivative tow so that the optical direction modifiers are interspersed among the elongate filaments ; and a resin supply , configured to provide a resin to be applied to at least one of the precursor tow dispensed from the filament supply , the individual ones of the elongate filaments or the subsets of the elongate filaments , originating from the filament separator , the optical direction modifiers , dispensed from the optical-direction-modifier supply , or the derivative tow , originating from the combiner , such that the elongate filaments and the optical direction modifiers in the derivative tow are covered with the resin . <EOS>