Patent ID: 8735768

Claim:
A laser welding apparatus for welding by a laser beam, comprising: a laser light source that emits the laser beam; a first optical element that coaxially emits, to a welded part, the laser beam and an object beam having a different wavelength from the laser beam; a second optical element that causes a spot diameter of the object beam to be larger than a spot diameter of the laser beam on the welded part; an optical interferometer that emits the object beam to the first optical element, detects through the first optical element the object beam reflected on the welded part, and generates an electric signal; a measuring unit that measures a penetration depth of the welded part based on the electric signal; and an evaluating unit that evaluates the welded part based on the penetration depth of the welded part, wherein the optical interferometer generates a coherent beam from the object beam and a reference beam, and generates the electric signal based on the coherent beam according to a difference in optical path length between the object beam and the reference beam, wherein the optical interferometer comprises: a wavelength-scanning light source that emits the object beam periodically varying in wavelength; a fiber coupler that splits the object beam reflected on the welded part; and a differential detector that converts, into electric signals, the object beam split by the fiber coupler and generates a differential component between the electric signals, and wherein the measuring unit measures the penetration depth of the welded part based on the differential component.