Laser processing method and laser processing device

A laser processing device for scanning over a first member in a first direction while irradiating the first member with a laser beam, and joining the first member and a second member adjacent to the first member by a molten portion, the laser processing device comprising:

• an oscillator configured to emit the laser beam;
• an irradiation optical system configured to guide the laser beam to the first member;
• a stage configured to move the first member and the second member relative to the laser beam to cause the laser beam to scan in the first direction;
• a measurement optical system configured to guide, from each of a first measurement region, a second measurement region different from the first measurement region, and a third measurement region different from the first measurement region and the second measurement region, a welding light radiated from at least one of the first member or the second member by irradiation with the laser beam, the welding light including at least one of a heat radiation light, a plasma light, or a reflected light;
• a first sensor configured to measure a first intensity of the welding light guided from the first measurement region to the measurement optical system;
• a second sensor configured to measure a second intensity of the welding light guided from the second measurement region to the measurement optical system;
• a third sensor configured to measure a third intensity of the welding light guided from the third measurement region to the measurement optical system;
• and
• a determination unit configured to evaluate a state of a laser processing based on the first intensity, the second intensity, and the third intensity,
• wherein:
• the first measurement region, the second measurement region, and the third measurement region are aligned adjacent to each other in a second direction intersecting the first direction;
• the first measurement region is located in the molten portion and sandwiched between the second measurement region and the third measurement region;
• and
• the determination unit is further configured to determine that a melting abnormality has occurred on one side of the molten portion in the second direction based on a relative relationship between the intensities measured in adjacent measurement regions of the first, second, and third measurement regions.