Abstract: In a method for treating carbon nanotube-based material, the carbon nanotube-based material is suspended in an oxidative atmosphere. An illumination portion is illuminated with electromagnetic radiation to heat the illumination portion, the illumination portion being out of direct contact with any supporting surface. Heat is continuously conducted away from the illumination portion to a non-illumination portion of the carbon nanotube-based material. This heating in the oxidative atmosphere causes at least partial oxidation and at least partial removal of amorphous carbon, partly ordered non-tubular carbon, and/or defective nanotubes in the carbon nanotube-based material, leaving a treated material comprising an arrangement of remaining carbon nanotubes.