To prevent laser beams from being absorbed, reflected and scattered by water drops by providing a gas flow passage on the peripheral wall of a body part of an underwater laser beam torch, and guiding the dry gas supplied to a first space between the tail end of the optical fiber and a lens to a second space between the lens and the tip opening thereby constantly drying the optical fiber end part and the lens.
During the underwater welding, an underwater laser beam torch is erected approximately perpendicular to a base material 10, and a tip opening 3 is detached from the prescribed distance from the surface of the base metal 10. The laser beams are transmitted from the optical fiber 1, and emitted from an optical fiber end part 1a and converged by a lens 4, and radiated from a tip opening 3. The inert gas 12 is supplied to a first space 5 from a main gas supply part 8, and the inert gas 12 is supplied to a second space 6 from an auxiliary gas supply part 9. The inert gas 12 is supplied in the dry condition. The inert gas 12 supplied to the first space 5 keeps the optical fiber end part 1a and the surface of the lens 4 in a dry condition, and flows into the second space 6 through the gas flow passage 7 provided in the body part 2.
OWAKI KATSURA
TSUCHIYA KAZUYUKI
YAMAOKA HIROTO
NISHIMI AKIHIRO
