Optical resonator, and laser processing apparatus

An optical resonator of wavelength beam combining type that combines a plurality of light beams having different wavelengths, including:

• a laser diode array having a plurality of laser elements arranged along a predetermined direction and configured to emit light beams having wavelengths different from one another;
• a diffraction grating that diffracts the light beam emitted from each of the laser elements at a diffraction angle corresponding to the wavelength of the light beam;
• an output coupler that reflects a part of the light beam diffracted by the diffraction grating toward each of the laser elements;
• and
• an optical system provided between the laser diode array and the diffraction grating and configured to align the light beams emitted from the laser elements with one another;
• wherein the optical system includes, in a sequence from the laser diode array toward the diffraction grating, a first lens element having a negative power only in the predetermined direction and a second lens element having a positive power only in the predetermined direction, and
• wherein the optical resonator satisfies the following expression:
• f
• 1
• ⁢
• f
• 2
• f
• 1
• ⁢
• f
• 2
• +
• f
• 1
• ⁢
• s
• -
• s
• 2
• ≥
• 1333.333
• ⁢
• (
• 1
• 4000
• ⁢
• m
• )
• 2
• -
• (
• λ
• 2
• )
• 2
• where, f1 is a focal length of the second lens element, f2 is a focal length of the first lens element, s is a distance from an object-side principal plane of the first lens element to an image-side principal plane of the second lens element, m is a diffraction order of the diffraction grating, and λ is a resonance wavelength.