Abstract: The device comprises an optical waveguide and an acoustic wave generating device. The waveguide has an optical band gap and a sharp electronic transition (e.g. an excitonic transition) in the band gap, and the acoustic wave generating device generates acoustic waves within the waveguide. Light passing through the waveguide is of a frequency within the band gap of the waveguide and is nearly resonant with the sharp electronic transition. The wave generating device is arranged to generate acoustic waves so as to induce optical band gas in the polariton spectrum, thereby affecting the transmission of the light passing through the waveguide, the transmission of which is thereby affected.

Abstract: Apparatus for automatic welding of complex contours made up of rectilinear and curvilinear portions. Such apparatus includes first and second movable carriages guided for reciprocation in directions parallel to each other and having a welding torch, a driving unit, and a gear rack with which a driving gear is permanently in mesh. The gear rack is permanently affixed to a first one of said carriages whereas the driving gear is mounted upon a shaft fixedly journalled upon the other of the carriages. The first and second moving carriages are mounted on first and second drive screws, respectively, which are connected to the driving unit by means of a selective motion reversing mechanism. The welding torch is affixed to the shaft bearing the gear which is in mesh with the rack. If suitable torches are used, the apparatus can also be used for cutting, building-up, and surfacing operations.