13  kW monolithic linearly polarized single-mode master oscillator power amplifier and strategies for mitigating mode instabilities

Abstract

Abstract:We report on the high power amplification of 1064nm linearlypolarized laser in all-fiber polarization-maintained MOPA, which can operate at output power level of 1.3kW. The main amplifier was pumped with six 915nm laser diodes, and the slope efficiency is 65.3%. The beam quality (M 2 ) was measured to be <1.2 at full power operation. The polarization extinction rate of the fiber amplifier was measured to be above 94% before mode instabilities (MI) sets in, which reduced to about 90% after the onset of MI. Power scaling capability of strategies for suppressing MI is analyzed based on a novel semi-analytical model, the theoretical results of which agree with the experimental results. It shows that mitigating MI by coiling the gain fiber is an effective and practical way in standard double-cladding large mode area fiber, and, by tight coiling of the gain fiber to the radius of 5.5cm, the MI threshold can be increased to 3 times higher than that without coiling or loose coiling. Experimental study has been carried out to verify the idea, which has proved that MI was suppressed successfully in the amplifier by tight coiling.

315 kW direct diode-pumped near diffraction-limited all-fiber-integrated fiber laser

“…By coiling the fiber, the high-order modes can be leaked into the inner cladding and then stripped by the homedesigned cladding mode stripper. The coiling diameter of the fiber is about 12 cm, based on the analysis of [15]. Finally, near diffraction-limited beam quality is achieved.…”

Study of Wavelength Dependence of Mode Instability Based on a Semi-Analytical Model

“…This physical principal has been employed widely in theoretical study of MI [4][5][6][7][8][9][10][11][12][13][14][15], and agrees with the experimental observation. So this physical principle is employed as the physical basis of our theoretical model in [20]. However, the heat due to the absorption in the fiber has not been taken into consideration in [20].…”

“…So this physical principle is employed as the physical basis of our theoretical model in [20]. However, the heat due to the absorption in the fiber has not been taken into consideration in [20]. Assuming that all the power absorbed due to linear absorption is turned into heat, the volume heat-generation density Q can be approximately expressed as…”

“…The meaning of the symbols is the same as in [20], where / C     ,  is the density, C is the specific heat capacity, κ is the thermal conductivity, η is the thermal-optic coefficient, and ω is the angular frequency of the mode.…”

15 kW ytterbium-doped single-transverse-mode, linearly polarized monolithic fiber master oscillator power amplifier

“…In nonlinearly polarized fiber lasers with output power more than 3 kW, most of them were achieved with the MOPA structure. Last year, our group have demonstrated a linearly polarized MOPA with output power of 1.3 kW based on a multistage cascaded structure, while mode instability (MI) began to arise at output power of 1.26 kW [18]. Multistage amplification was employed due to the relatively low power of the seed laser (<100 mW), which made the system relatively complex.…”