Patent ID: 7426223

Claim:
A coherent light source, comprising: a light source; a wavelength conversion element that converts part of a fundamental wave emitted from the light source into a higher harmonic wave; and a wavelength selecting filter that has narrow-band transmission characteristics with respect to the part of the fundamental wave not converted into the higher harmonic wave, and has transmission characteristics with respect to the higher harmonic wave, wherein the part of the fundamental wave emitted from the wavelength conversion element but not converted into the higher harmonic wave is fed back to the light source by the wavelength selecting filter, the higher harmonic wave is emitted to the outside after passing through the wavelength selecting filter, the wavelength selecting filter includes a mechanism to vary an angle with respect to the fundamental wave, thereby adjusting a transmitted wavelength, and Δλ 2 >λ 1 is satisfied, wherein Δλ 1 is a transmitted wavelength bandwidth for the fundamental wave in the wavelength selecting filter and Δλ 2 is a transmitted wavelength bandwidth for the higher harmonic wave in the wavelength selecting filter.