Patent 7218653 was granted and assigned to Mitsubishi Materials on May, 2007 by the United States Patent and Trademark Office.
An ultraviolet laser is provided that increases the conversion efficiency of laser beams when harmonics having wavelengths of less than 355 nm are generated by converting laser beams with a wavelength conversion element made of a single crystal of lithium tetraborate. A wavelength conversion element is heated and controlled to a specific temperature (for example, 200° C.) within a temperature range of 200 to 450° C. with a predetermined temperature precision.