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.