An Er:YAG laser includes an Er:YAG crystal medium and optical pumping element and is adapted to oscillate at a wavelength of 2.94 μm. The optical pumping element irradiates pumping light pulses onto a plurality of regions along a longitudinal direction of the Er:YAG crystal medium from its side at timings offset from each other, thereby exciting the respective regions. By exciting the spatial regions of the laser medium in a time-sharing manner, Er ions in an unexcited region of a 4I13/2 level serving as a lower level in the 2.94 μm-wavelength laser are reduced by a non-radiation process and, therefore, it is possible to achieve the increase in power of the 2.94 μm-wavelength laser output of the Er:YAG laser.
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