Light source device

A light source device comprising:

• a light source part comprising a plurality of laser light sources, each laser light source being configured to emit light having a predetermined wavelength width;
• a plurality of collimators, each configured to convert light emitted from a corresponding one of the laser light sources into substantially parallel light;
• a light-condensing part configured to adjust light emitted from the collimators into parallel light and to condense the parallel light;
• a diffraction grating configured to receive the condensed light;
• an output coupler disposed in an optical path of diffracted light from the diffraction grating so as to form an external resonator with the laser light sources, wherein a reflecting surface of the output coupler is a depressed surface;
• and
• an adjusting lens disposed downstream of the output coupler, the adjusting lens being configured to convert light emitted from the output coupler into substantially parallel light or to condense light emitted from the output coupler.