Patent ID: 7940458

Claim:
A laser light source device, comprising: a laser light source that emits multimode laser light; an optical element that collimates the laser light emitted from the laser light source; a diffraction grating having a surface that reflects zero-order light in the collimated laser light in a predetermined direction other than a direction toward the laser light source and reflects first-order light in the collimated laser light toward the laser light source; a partially transmissive mirror having a surface that reflects the zero-order light reflected by the diffraction grating in a predetermined direction while transmitting a part of the zero-order light reflected by the diffraction grating; a shear plate including opposing first and second surfaces with an angle between the opposing first and second surfaces being several tens of degrees, wherein the shear plate is disposed in an optical path of the light reflected by the partially transmissive mirror, such that the light reflected by the partially transmissive mirror is incident on the first surface of the shear plate at an angle of 45′; and a device to detect a wavelength of light and including (i) a first detector that detects a position of the light that passes through the partially transmissive mirror and (ii) a second detector that detects an intensity of light reflected by the shear plate at a number of positions of an interference fringe formed from the light reflected by the partially transmissive mirror which is incident on the first and second surfaces of the shear plate, said device detecting the wavelength of the light using results from both the first detector and the second detector; and control means for controlling movement of the partially transmissive mirror with the diffraction grating, wherein, when the partially transmissive mirror with the diffraction grating moves based on control by the control means, an incidence angle of the laser light on the surface of the diffraction grating is changed while an angle between the surface of the diffraction grating and the surface of the partially transmissive mirror is maintained at a predetermined angle.