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10 December 2014780W narrow linewidth all fiber laser with sinusoidal phase modulation
In high power fiber laser, the limiting factor of narrow linewidth output is analyzed. The
influence of Stimulated Brillouin scattering effect and sinusoidal phase modulation suppressing
method are studied. The linewidth of a single frequency laser is broadened from 1MHz to 2.9 GHz by sinusoidal phase modulation technology. The output power of single frequency laser is 50mW.
And through three stage fiber amplified, the central wavelength of 1064.34nm, linewidth of 2.9 GHz
and power of 780W are achieved respectively. The optical-optical efficiency is 79%. And the beam
quality is [see manuscript] and [see manuscript]. The distributing characteristic of longitudinal mode, under
every modulating coefficient, is measured. And the result is the same as theoretical result. The
increasing of longitudinal mode number, controlling of longitudinal mode spacing and reducing
power spectrum density by sinusoidal phase modulation are proved to be viable. Then Stimulated
Brillouin Scattering threshold is increased. Finally, the output power is increased a lot. The output
power of this laser is only limited by pump power. If the pump power is increased, the higher power
of narrow linewidth fiber laser will be achieved.