A laser amplifier includes a gain medium of a glass fiber, a first exciting light
source, a second exciting light source, and another first exciting light source.
The gain medium of the glass fiber includes rare earth dopant in a host medium.
Ions of the rare earth dopant has an energy level structure including a ground
level and a pair of laser upper level and laser lower levels between which a stimulated
transition is to be produced after production of a population inversion between
the pair of laser upper and laser lower levels. The pair of laser upper and laser
lower levels being higher than the ground level. The first exciting light source
is coupled to the input side of the glass fiber for introducing first exciting
light to the glass fiber to produce the population inversion. The second exciting
light source is coupled to the input side of the glass fiber for introducing second
exciting light source to the glass fiber to raise ions of the rare earth dopant
from the ground level to the laser lower level. The second exciting light has a
wavelength band different from a wavelength band of the first exciting light. The
other first exciting light source is coupled to the output side of the glass fiber
for introducing the first exciting light to the glass fiber. A two-way excitation
is performed on the glass fiber.
