Laser machining device and laser machining method

A laser processing device for converging laser light at an object to be processed so as to form a modified region within the object along a line to cut, the laser processing device comprising:

• a laser light source emitting the laser light;
• a converging optical system converging the laser light emitted from the laser light source at the object;
• a spatial light modulator modulating the laser light emitted from the laser light source such that the laser light is caused to branch into at least first processing light and second processing light, and the first processing light is converged at a first converging point and the second processing light is converged at a second converging point by the converging optical system, and
• an adjustment optical system having a first optical element and a second optical element, each of which functions as a lens, wherein
• the first converging point and the second converging point have a positional relationship in which the first converging point is positioned at a first surface side as an opposite side to a laser light entrance side of the object with respect to the second converging point, and the first converging point is positioned at an anterior side in a moving direction of the laser light along the line to cut with respect to the second converging point, in the object,
• in a case in which W1 is a radius of the first processing light at the first surface, W2 is a radius of the second processing light at the first surface, and D is a distance between the first converging point and the second converging point when viewed from a direction orthogonal to the first surface, the spatial light modulator modulates the laser light such that D>W1+W2 is satisfied,
• the first optical element and the second optical element are arranged such that a distance of an optical path between the spatial light modulator and the first optical element equals a first focal length of the first optical element, a distance of an optical path between the converging optical system and the second optical element equals a second focal length of the second optical element, a distance of an optical path between the first optical element and the second optical element equals a sum of the first focal length and the second focal length, and the first optical element and the second optical element constitute a double-telecentric optical system,
• the spatial light modulator has a plurality of pixels for displaying a modulation pattern, and
• in a case in which d is a distance between the pixels adjacent to each other, m is a magnification of the adjustment optical system, f is a focal length of the converging optical system, and λ is a wavelength of the laser light, the spatial light modulator modulates the laser light such that D<2×f×tan[a sin{λ(d×4×m)}] is satisfied.