Patent ID: 8008600

Claim:
A fiber laser apparatus comprising: a seed light source outputting seed light; an amplifying section for amplifying the seed light by cladding-pumping, said amplifying section including: an amplifying optical fiber having a core extending along a predetermined axis, an inner cladding provided on an outer periphery of said core and having a refractive index lower than that of said core, and an outer cladding provided on an outer periphery of said inner cladding and having a refractive index lower than that of said inner cladding; an pumping light source outputting pumping light; and an optical multiplexers for supplying the seed light from said seed light source to said core of said amplifying optical fiber and supplying the pumping light from said pumping light source to said inner cladding of said amplifying optical fiber, whereby said amplifying optical fiber outputs single-mode amplified seed light that is amplified by cladding-pumping together with multimode residual pumping light; an output optical system irradiating an object with the single-mode amplified seed light and multimode residual pumping light that are outputted from said amplifying optical fiber, said output optical system converging the single-mode amplified seed light on the object; and a guiding optical fiber, for guiding the single-mode amplified seed light and multimode residual pumping light that are outputted from said amplifying optical fiber to said output optical system, provided between said amplifying optical fiber and said output optical system, said guiding optical fiber having a core extending along a predetermined axis, an inner cladding provided on an outer periphery of said core and having a refractive index lower than that of said core, and an outer cladding provided on an outer periphery of said inner cladding and having a refractive index lower than that of said inner cladding, whereby the single-mode amplified seed light outputted from said amplifying optical fiber propagates mainly in said core of said guiding optical fiber, and the multimode residual pumping light outputted from said amplifying optical fiber propagates mainly in said core and inner cladding of said guiding optical fiber.