Wavelength conversion laser apparatus

The present invention is a wavelength conversion laser apparatus for converting wavelength by utilizing a nonlinear optical crystal and capable of safely using it over a long time. For this end, the fundamental wave laser light emitted from the pumping chamber unit which is a solid state laser light source is converted into the second harmonic wave by the first nonlinear optical crystal unit . And the second harmonic wave is, then, converted into the third (or fourth) harmonic wave by the second nonlinear optical crystal unit . Filled in the container for each of the nonlinear optical crystal units is a dry inert gas. A humidity sensor detects humidity inside the container. The output from the humidity sensor is supplied to the laser control portion . When the detected humidity exceeds a predetermined value, the laser oscillation is interrupted, thereby preventing the nonlinear optical crystal from being damaged in case of any defect in the sealing structure of the container.