Laser light emitted from an LD apparatus is concentrated and applied onto a
laser light path region A of a slab-shaped YAG crystal 21 and the
neighborhood thereof with the use of a concave lens and a pair of
reflecting mirrors, a duct lens, or a plurality of cylindrical lenses,
whereby a concentrated applied light intensity distribution in the side
surface width direction (y-axis direction) of the slab-shaped YAG crystal
is formed as a double-peak distribution having maximum values P.sub.1 and
P.sub.2 at opposite end portions A.sub.1 and A.sub.2 of the laser light
path region of the slab-shaped YAG crystal or in the neighborhoods
thereof.
