A welding method includes: irradiating a plurality of metal foils stacked on a first surface of a metal member in a first direction with laser light to weld the metal member and the plurality of metal foils to each other, the laser light including first laser light having a wavelength of 800 [nm] or more and 1200 [nm] or less and second laser light having a wavelength of 550 [nm] or less, a second surface of a metal foil farthest from the metal member in the first direction among the plurality of metal foils, on a side opposite to the metal member, being irradiated with the laser light.

A laser irradiation apparatus including: a laser light source configured to emit a linearly polarized pulsed laser light; a first half-wave plate rotatably provided in an optical path of the pulsed laser light; a first polarization beam splitter configured to branch the pulsed laser light from the first half-wave plate into a first pulsed light and a second pulsed light; a second polarization beam splitter configured to combined the first pulsed light with the second pulsed light, the second pulsed light, the second pulsed light being delayed from the first pulsed light by using an optical path length difference between the first pulsed light and the second pulsed light; and a first wave plate rotatably provided in an optical path of a combined pulsed light generated by combining the first pulsed light with the second pulsed light at the second polarization beam splitter.

A method for welding coated steel sheets, particularly steel sheets that are coated with an aluminum-silicon metallic coating layer, is provided. A configuration of two laser beams is provided, wherein the laser beams act on a weld pool that is to be formed, at least one laser beam rotates around a rotation axis so that the laser beams execute a movement relative to each other, and the laser beams are guided along a welding axis. In order to achieve a mixing of the weld pool, a defined stirring effect and a defined welding speed in relation to each other are adhered to, wherein a mathematically defined condition applies to the stirring effect.

A laser welding device includes a support that supports a base material, an irradiation unit that irradiates the base material with a laser beam, and a drive mechanism that moves the irradiation unit relative to the base material to scan the laser beam, and the drive mechanism moves the laser beam relative to the base material in a posture in which an optical axis of the laser beam is tilted backward with respect to a scanning direction.

Laser processing head 10 includes housing 11 and a plurality of optical components. Housing 11 is provided with partition wall 11a, first and second light entrance ports 12a, 12b through which first and second laser beams A, B respectively enter, and light irradiation port 13. Laser processing head 10 includes first and second photodetectors 91b, 92a provided around first and second light entrance ports 12a, 12b, respectively. First photodetector 91b is disposed opposite to second photodetector 92a across partition wall 11a. First photodetector 91b receives light in the second wavelength band including the wavelength of second laser beam B, and second photodetector 92a receives light in the first wavelength band including the wavelength of first laser beam A.

A wavelength beam combining device includes: a polarization beam splitter configured to separate the plurality of laser beams into a plurality of first polarized light beams linearly polarized in a first polarization direction and a plurality of second polarized light beams linearly polarized in a second polarization direction that is orthogonal to the first polarization direction; a first polarization conversion element configured to convert the second polarized light beams into a plurality of third polarized light beams linearly polarized in the first polarization direction; a diffraction grating configured to diffract the plurality of first polarized light beams and generate a coaxially combined first wavelength-combined beam, and to diffract the plurality of third polarized light beams and generate a coaxially combined second wavelength-combined beam; and a polarization beam combiner configured to generate and emit a third wavelength-combined beam into which the first wavelength-combined beam and the second wavelength-combined beam have been coaxially combined.

A light source module that emits a combined laser beam, and includes: a plurality of semiconductor laser elements; and a control circuit that controls power of a laser beam emitted by each of the semiconductor laser elements. The semiconductor laser elements include: a first element group that emits a first laser beam; and a second element group that emits a second laser beam. The combined laser beam includes at least one of the first laser beam or the second laser beam. The control circuit maintains an average combined-beam wavelength that is an average wavelength of the combined laser beam constant for a change in power of the combined laser beam. When the power of the first laser beam and the power of the second laser beam are equal to each other, an average wavelength of the first laser beam is longer than an average wavelength of the second laser beam.

Laser processing head 10 includes housing 11 and a plurality of optical components. Housing 11 is provided with partition wall 11a, first and second light entrance ports 12a, 12b through which first and second laser beams A, B respectively enter, and light irradiation port 13. Laser processing head 10 includes first and second photodetectors 91b, 92a provided around first and second light entrance ports 12a, 12b, respectively. First photodetector 91b is disposed opposite to second photodetector 92a across partition wall 11a. First photodetector 91b receives light in the second wavelength band including the wavelength of second laser beam B, and second photodetector 92a receives light in the first wavelength band including the wavelength of first laser beam A.