中文摘要：

高功率单频激光在激光雷达、光谱学、精密测量等领域具有广阔的应用前景.采用中心波长为1064nm、光谱线宽为20kHz、偏振消光比（PER）高于20dB的单频线偏振分布式反馈光纤激光器做种子源（尾纤输出功率约为10mW）,利用种子注入主振荡功率光纤放大技术,通过两级级联放大实现了128W高功率单频、线偏振、近衍射极限单模连续激光输出.主放大器光-光效率达到83%,PER高于12dB.采用分段温控技术有效地提高了光纤中的受激布里渊散射（SBS）阈值,实验中未观察到明显的放大自发辐射和SBS现象,进一步提高抽运功率有望获得更高的放大激光输出.

英文摘要：

High power single-frequency （SF） lasers are of great significance in science,industry,and defense applications such as gravitational wave detection,free apace optical communication,range finding,lidar,parametric wavelength conversion in resonant cavities. We report on a high power single-frequency linearly polarized radiation with a nearly diffraction-limited beam quality by use of a two-stage fiber master-oscillator power amplifier system. The master oscillator is an SF distribution feedback fiber laser with polarization maintaining （PM） and single mode （SM） fiber pigtailed output power of about 10 mW at 1064 nm,and its line-width is of 20 kHz. This light power is amplified to about 1 W by the first stage of all-fiber SM/PM amplifier and then seeded at the second stage of high power main amplifier with large mode area （LMA） ytterbium-doped fiber （YDF）. The pumping diode laser of the main amplifier is fiber-coupled （the core diameter is 400 μm and corresponding numerical aperture is 0. 22） with a max emitting power as high as 190 W at 976 nm. By employing the co-pump configuration with a space coupling efficiency of about 85% ,we demonstrate that the power output from the LMA/PM YDF （ core diameter is 20 μm,inner cladding diameter is 400 μm） reaches 128 W and its corresponding overall slope-efficiency is 85% of the launched pump power. The beam profile is diffraction-limited and linearly polarized with a polarization extinction ratio over 12 dB. There is observed neither amplified spontaneous emission nor stimulated Brillouin scattering phenomenon,which means that the substitution of the pump source with the more powerful one can further enhance power output if LMA YDF with a larger core size,shorter fiber length and higher doping efficiency is used.