A waveguide is constructed by sandwiching a transparent member (4) and a laser medium (5) between a first clad 3-1 and a second clad 3-2. Pumping light (8) is made to be incident from a direction perpendicular to a direction of the optical axes of first to fourth laser oscillation light beams 9-1 to 9-4, and to alternately propagate through the transparent member (4) and the laser medium (5) in a zigzag manner so as to pump only resonator mode regions in the laser medium (5).
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