A semiconductor laser device which has a diffraction grating partially provided
in the vicinity of an active layer formed between a radiation-side reflection film
provided on a radiation-side end surface of a laser beam and a reflection film
provided on a reflection-side end surface of the laser beam, and which outputs
a laser beam having a desired oscillation longitudinal mode based on a wavelength
selection characteristic of at least the diffraction grating. The diffraction grating
is formed in isolation with an isolation distance of Ls=15 m from the radiation-side
reflection film.
