PURPOSE:To provide a short-pulse laser with high average output by furnishing an external resonator with a mode-locked surface-emission semiconductor laser, as an amplification medium, which emits light in the crystal growth direction. CONSTITUTION:An optical isolator 1 serves to prevent the reflection of pumping light from entering a laser. The pumping light 2 is a series of mode-locked pulses. A dichroic mirror 3 reflects the pumping light but transmits laser light. An external resonator is formed of a terminal reflector 4, transparent to signal light and reflecting laser light, and a gold-coated face of a semiconductor for amplification medium 5, the other face of which has reflective coating. A lens 6 converges light onto the semiconductor 5. In the above optical system, the pumping device is a mode-locked Nd YAG laser, and the semiconductor laser medium is a multiple quantum well InGaAs semiconductor.
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