Output characteristics of kW master-oscillator power amplifier fiber laser

The method of controlling mode with which a single mode laser output is achieved under high power is analyzed. Using master-oscillator power amplifier (MOPA), the continuous and single mode laser of 1.08 m wavelength, 1.05 kW maximum output power is obtained. The laser spectrum and beam quality as functions of laser power are studied. The results indicate that the center wavelength and beam quality remain unchanged, and the spectrum width broadens with the increase of laser power. The reason for the broadening of laser spectrum width is that as laser power becomes higher, the change of refractive index of fiber grating core increases, which induces the spectrum broadening of master oscillator stage. Also, the noise induced by the spectrum broadening of master oscillator stage is amplified in amplifier stage, which combined with spontaneous radiation induced by amplifier makes the spectrum width of amplifier stage broaden. Moreover, the reason that the beam quality worsens is that part of the laser transmitting in the fiber core leaks to inner cladding due to fiber bending.