Abstract: To produce blue light by means of a laser, pumped light is coupled into a birefringent, nonlinear crystal (5) in a variable frequency laser (1) from a laser diode pumped light source (7, 8, 9) via an input mirror (3). Due to adjustment of the inclination of the crystal (5) or with the aid of tempering means (6) for the crystal, most of the pumped light is absorbed in the crystal (5)--upon suitable polarization of the pumped light--while the rest is available for a frequency mixture of the fundamental Wave of the laser and of the pumped light. Via an output mirror (4) blue laser light with a Wavelength of e.g. 459 nm is coupled out, with a fundamental wave of e.g. 1064 nm and pumped light with a wavelength of e.g. 806 nm.