There has been invented a method and apparatus for heat treating or brazing joints in metals and ceramics using an optical concentrator (reflecting waveguide) to reflect energy from infrared energy heat sources, in a pattern which will provide precisely tailored illumination, heating, melting of filler and fusion of the area to be heat treated or the joint to be formed. CAD optical ray tracing software is used to custom design the reflecting waveguides for directing the energy as needed. With the invention, shorter, reduced energy heat cycles can be used to produce reliable accurate brazes, including brazes to join small diameter tubes. No furnace is necessary because localized small area brazing can be done in situ with the invention method and apparatus. Various heat sources can be used to braze various geometries, including very small diameter tubes.