Abstract: 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 ?m. 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 ?m-wavelength laser are reduced by a non-radiation process and, therefore, it is possible to achieve the increase in power of the 2.94 ?m-wavelength laser output of the Er:YAG laser.

Abstract: The disclosure relates to a device for preventing tooth decay by use of laser beams and to a method of preventing tooth decay by use of such a device. According to the invention, high-speed repetition pulses projected from Q-switched continuous excitation Nd:YAG laser is irradiated upon teeth through a glass beam guide, whereby treatment of the teeth is reduced in time, is safe, effective and is readily useable for use by general practice.