A solid-state laser crystal constituting a laser-diode-excited solid-state
laser apparatus or an optical fiber constituting a fiber laser apparatus
or fiber laser amplifier is doped with one of Ho.sup.3+, Sm.sup.3+,
Eu.sup.3+, Dy.sup.3+, Er.sup.3+, and Tb.sup.3+ so that a laser beam is
emitted from the solid-state laser crystal or the optical fiber, or
incident light of the fiber laser amplifier is amplified, by one of the
transitions from .sup.5S.sub.2 to .sup.5I.sub.7, from .sup.5S.sub.2 to
.sup.5I.sub.8, from .sup.4G.sub.5/2 to .sup.6H.sub.5/2, from
.sup.4G.sub.5/2 to .sup.6H.sub.7/2, from .sup.4F.sub.3/2 to
.sup.6H.sub.11/2, from .sup.5D.sub.0 to .sup.7F.sub.2, from
.sup.4F.sub.9/2 to .sup.6H.sub.13/2, from .sup.4F.sub.9/2 to
.sup.6H.sub.11/2, from .sup.4S.sub.3/2 to .sup.4I.sub.15/2, from
.sup.2H.sub.9/2 to .sup.4I.sub.13/2, and from .sup.5D.sub.4 to
.sup.7F.sub.5. The above solid-state laser-crystal or optical fiber is
excited with a GaN-based compound laser diode.
