<p>The invention provides a compact laser light source whose wavelength can be designed freely in a wavelength band in which the semiconductor laser has not been put to practical use by combining an efficient nonlinear optical crystal and high-power semiconductor lasers for optical communication. In one embodiment, the laser light source includes: a first laser for generating a laser beam of a wavelength » 1 ; a second laser for generating a laser beam of a wavelength » 2 ; and a nonlinear optical crystal that allows the laser beam of wavelength » 1 and the laser beam of wavelength » 2 as inputs and outputs a coherent beam having a wavelength » 3 of a sum frequency that satisfies a relationship of 1/» 1 + 1/» 2 = 1/» 3 . The wavelength » 3 of the sum frequency is 589.3±2 nm that is equivalent to the sodium D line.</p>
