Wavelength combining
laser device (10) comprising the following: a
semiconductor laser (1) to emit a plurality of
laser beams (6) in a direction of an
optical axis from a light-emitting end face (1b) of the plurality of light-emitting areas (1a) arranged in a laser beam combination direction, wherein the direction of the
optical axis is perpendicular to the laser beam combination direction; a focusing element (2) that collimates the
laser beams (6); a
wavelength combining element (3) to combine the plurality of
laser beams (6) in the laser beam combination direction into a single laser beam (6) and to output the single laser beam (6); an optical
system (4) for cross-
coupling reduction, which has a positive refractive power in the laser beam combination direction perpendicular to an
optical axis of the individual laser beam (6) emitted by the
wavelength-combining element (3); and a partially reflective mirror (5) to reflect the single laser beam (6) which passes through the optical
system (4) for cross-
coupling reduction, and to allow the single laser beam (6) to transmit through and exit the partially reflective mirror (5), wherein the optical
system (4) is arranged to reduce cross-
coupling by imaging the light-emitting face (1b) onto the partially reflective mirror (5) by causing the light-emitting face (1b) to be conjugated with the partially reflective mirror (5) in a plane spanned by the optical axis of the single laser beam (6) and the laser beam combination direction, wherein the optical system (4) for cross-coupling reduction comprises two lenses (41, 42; 43, 44) which have an effect in the laser beam combination direction perpendicular to the direction of the optical axis of the individual laser beam (6) and satisfy a relation f1>f2, where f1 is a
focal length in the laser beam combination direction of the first lens (41, 43) which is arranged on a side that is closer to the
wavelength-combining element (3), and where f2 is a
focal length in the laser beam combination direction of a second lens (42, 44) which is arranged on a side that is closer to the partially reflective mirror (5), and a distance L between the first lens (41, 43) and the second lens (42, 44) L>f1+f2 is satisfied, wherein a common principal lens surface (H) of the first lens (41, 43) and the second lens (42, 44) is positioned on a side that is closer to the
semiconductor laser (1) than to the wavelength-combining element (3).