Laser device and optical amplifier

An optical amplifier, comprising:

• a resonator;
• a plurality of solid gain media, having fluorescent spectra that at least partially overlap with each other, provided within the resonator, wherein said solid gain media are crystalline structure materials;
• and
• pumping means provided outside the resonator, for pumping the plurality of solid gain media, by causing at least one laser beam to enter the plurality of solid gain media as a pumping light beam;
• wherein:
• the entire fluorescent spectrum width of the plurality of solid gain media is greater than the fluorescent spectrum width of each solid gain medium,
• wherein the resonator is structured in such a manner that a seed light beam which is input into the resonator from the exterior of the resonator reciprocates within the resonator, and that the seed light is amplified by being passed, a plurality of times, through the plurality of solid gain media that have been pumped by the pumping means and output from the resonator, and
• wherein the number and wavelength of fluorescent peaks of each of the plurality of solid gain media are selected, and the solid gain media are arranged such that the entire fluorescent spectrum bandwidth becomes a desired value, wherein:
• the plurality of solid gain medium include Lu3Ga5O12;
• Gd3Sc2Al3O12 and Gd3Sc2Ga3O12 in this order from the direction in which the laser beam enters, each gain medium having fluorescent spectrum bandwidths of less than 1.6 nm, respectively, and the entire spectrum width becomes approximately 3 nm.