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以大模场面积光子晶体光纤飞秒激光系统为基频光源,利用非线性频率上转换的方法,获得了高功率高重复频率多波长的飞秒激光脉冲.理论分析并实验验证了聚焦透镜的焦距对倍频光横向模场分布的影响,透镜焦距越长,模场质量越好.在基频光平均功率为21.8W,脉冲宽度为110fs,重复频率为50MHz的条件下,经过二倍频、三倍频和四倍频获得波长分别为520,347和261nm的飞秒激光,其平均功率分别达10.5,4.7和2.14W.二倍频和三倍频的转换效率分别为48.2%和21.6%,二倍频到四倍频的转换效率为20.4%.采用互相关法测量得到261nm紫外激光的脉冲宽度为408fs.
The femtosecond laser pulse with high power and high repetition frequency and multi-wavelength was obtained by using the large-mode-area photonic crystal fiber femtosecond laser system as the light source of the fundamental frequency by using the nonlinear frequency up-conversion method. The theoretical analysis and experimental verification of the focusing lens Focal length of the octave transverse mode field distribution, the longer the lens focal length, the better the mode field quality.When the average fundamental frequency power of 21.8W, the pulse width of 110fs, the repetition frequency of 50MHz conditions, after double frequency , Third harmonic and fourth harmonic to obtain the wavelength of 520,347 and 261nm femtosecond laser, the average power of 10.5,4.7 and 2.14W respectively. The conversion efficiency of double and triple frequency were 48.2% and 21.6%, respectively, The conversion efficiency from the second harmonic to the fourth harmonic is 20.4%. The cross-correlation method was used to measure the pulse width of the 261nm UV laser at 408 fs.