| 摘要 |
PURPOSE:To prevent damage or breakdown of nonlinear optical crystal due to excessive power density of incident laser beam to nonlinear optical crystal by providing a particular half-mirror, a power density detector, a comparator and a light shielding mechanism. CONSTITUTION:A variable-wavelength laser device 11 which changes wavelength of laser beam 13a emitted therefrom by changing a relative incident angle for crystal surface of laser beam 13 incident to nonlinear optical crystal 16 is provided with a half-mirror 21 for branching the laser beam 13 incident to the nonlinear optical crystal 15, a power density detector 31 for detecting power density of branched laser beam 13, a comparator 33 for comparing a detected value of power density detector 31 with the present value and a light shielding mechanism 20 for shielding the laser beam 13 incident to the nonlinear optical crystal 16 based on an output of the comparator 33. The light shielding mechanism 20 is structured, for example, a shutter 26 adjacent to the optical axis of laser beam 13, a solenoid 30 to drive the shutter and a solenoid drive circuit 23 to drive the solenoid 30 based on an output of comparator 33.
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