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基于四波混频的反斯托克斯变换,被广泛应用于短波辐射高分辨率成像以及直接激发分子的电子跃迁等方面.为了实现更加高效的反斯托克斯变换,利用中心波长为810 nm脉冲宽度为120 fs的钛蓝宝石(Ti:sapphire)飞秒激光器作为抽运光源,在长度为0.5 m和3 m的光子晶体光纤中分别实现了高阶模和基膜的简并四波混频.实验中,采用的光子晶体光纤的零色散波长在820 nm附近.在基模相位匹配条件下,在560 nm附近实现了高效地反斯托克斯信号的产生,反斯托克斯信号与残余抽运信号的最大功率比为33:1;反斯托克斯信号和斯托克斯信号的最大功率比25:1;反斯托克斯信号最大功率转换效率P_a/P_(p0)为34%.抽运波长从790 nm逐渐增加到810 nm过程中,在长为3 m的光子晶体光纤中相位从不匹配状态转化为高阶模匹配状态后,再转化为基模匹配状态.通过实验研究得出了相位匹配程度随抽运功率、波长和光纤长度的变化规律,同时分析了造成理论计算与实验结果存在差异的主要因素.本文为研究在光子晶体光纤基模中实现相位匹配和产生高效反斯托克斯信号提供了理论和实验依据.
The anti-Stokes transform based on four-wave mixing is widely used in high-resolution imaging of shortwave radiation and the direct electronic excitation of molecules.In order to achieve more efficient anti-Stokes transform, the central wavelength of 810 nm Ti: sapphire femtosecond laser with a pulse width of 120 fs was used as a pumping light source to degenerate four-wave mixing of high-order mode and base-film respectively in photonic crystal fibers with length of 0.5 m and 3 m. In the experiment, the photonic crystal fiber used has a zero-dispersion wavelength around 820 nm, and produces an efficient anti-Stokes signal near 560 nm under the fundamental-mode phase matching condition. The anti-Stokes signal and residual The maximum power ratio of pumping signal is 33: 1; the maximum power ratio of anti-Stokes signal and Stokes signal is 25: 1; the maximum power conversion efficiency of anti-Stokes signal is P_a / P_ (p0) % .When the pumping wavelength is gradually increased from 790 nm to 810 nm, the phase transition from unmatched state to high order mode matched state in photonic crystal fiber with a length of 3 m is converted to the matched mode of basic mode. Out of the phase matching with pumping power Wavelength and fiber length, and analyzed the main factors causing the difference between the theoretical calculation and the experimental results.This paper provides the theory and experiment to study the phase matching and the generation of high-efficiency anti-Stokes signals in the fundamental mode of photonic crystal fiber in accordance with.