Patent ID: 8294979

Claim:
A wavelength conversion device, comprising: a laser light source that emits a fundamental wave; a wavelength conversion element that converts the fundamental wave into a second harmonic wave; and an optical system including a wavelength selective mirror that reflects the fundamental wave transmitted through the wavelength conversion element without being converted, while transmitting therethrough the second harmonic wave generated by wavelength conversion, wherein the optical system, which makes the fundamental wave enter the wavelength conversion element to be focused to have a focusing point in the wavelength conversion element, makes the fundamental wave, transmitted through the wavelength conversion element without being converted into the second harmonic wave, enter the wavelength conversion element again once or more than once to be subjected to wavelength conversion while being focused to have a focusing point in the wavelength conversion element by the wavelength selective mirror in such a manner that respective focusing points are scattered in the wavelength conversion element; and the conversion efficiency in at least one of the second stage and stages subsequent to the second stage is higher than the conversion efficiency in the first stage, where the conversion efficiency in each stage is defined as: (a second harmonic wave generated in one stage)/(a square of the fundamental wave entered in said one stage).