Optical wavelength conversion method, optical wavelength conversion system, program and medium, and laser oscillation system

An optical wavelength conversion process for allowing light from a laser oscillator that oscillates coherent light with a natural wavelength lambda to be incident to a nonlinear optical crystal as an incident light and light with a wavelength 1/2 lambda to be output. The wavelength of the incident light is up to 1,000 nm and the peak power density of the incident light is 0.1-10 times the peak power density that gives a maximum conversion efficiency. Alternatively, the above nonlinear optical crystal is heated and kept at 200-600 degrees C. In addition, a fundamental harmonic is sequentially shone into a first crystal and a second crystal, with the first crystal being larger in bulk damage threshold value with respect to a fundamental harmonic than the second crystal and the second crystal being larger in effective non-linear constant with respect to the fundamental harmonic than the first crystal.