US Patent 7397598 Light source unit and light irradiation unit

In nonlinear optical crystal 183D, each step of wavelength conversion can be performed using another fundamental wave that is output from light output unit 1612, without using the fundamental wave whose output level has been attenuated after going through wavelength conversion for several steps (wavelength conversion in nonlinear optical crystals 183A to 183C). Therefore, the wavelength conversion efficiency improves and the peak power of optical amplifiers 1611 and 1612 can be suppressed, which allows the wavelength of lights that are output from optical amplifiers 1611 and 1612 to be further narrowed.