Nonlinear optics in the extreme ultraviolet
Nonlinear optics in the extreme ultraviolet
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DOI：
10.1038/nature03108
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发表时间：
2004-12-02
期刊：
影响因子：
64.8
通讯作者：
Watanabe, S
中科院分区：
文献类型：
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作者：
Sekikawa, T;Kosuge, A;Watanabe, S
对光场的非线性响应在本质上是普遍的，但由于缺乏相干强光源，在极紫外（XUV）和软X射线区域中难以观察到。高次谐波产生是一种众所周知的非线性光学现象（1，2），现在在阿秒脉冲产生中引起了广泛的关注（3-6）。为了将高次谐波应用于XUV和软X射线领域的非线性光学，光脉冲应该具有大的脉冲能量和短的脉冲持续时间以实现高的光学电场。在这里，我们展示了通过使用亚10飞秒蓝色激光脉冲从单次谐波（光子能量27.9 eV）产生强烈的隔离脉冲，在相对较低的（第九）谐波阶非线性地产生大的偶极矩（7，8）。脉冲持续时间为950阿秒和1.3飞秒的XUV脉冲通过基于氦原子的双光子阈上电离（9）的自相关技术来表征。由于阈值以上电离的横截面较小（10），因此迄今为止尚未证明光子能量大于氦电离能的XUV脉冲的这种自相关测量（6，11 -13）。该技术可以扩展到在较短波长的高次谐波的表征。
Nonlinear responses to an optical field are universal in nature but have been difficult to observe in the extreme ultraviolet (XUV) and soft X-ray regions owing to a lack of coherent intense light sources. High harmonic generation is a well-known nonlinear optical phenomenon(1,2) and is now drawing much attention in attosecond pulse generation(3-6). For the application of high harmonics to nonlinear optics in the XUV and soft X-ray regime, optical pulses should have both large pulse energy and short pulse duration to achieve a high optical electric field. Here we show the generation of intense isolated pulses from a single harmonic (photon energy 27.9 eV) by using a sub-10-femtosecond blue laser pulse, producing a large dipole moment at the relatively low ( ninth) harmonic order nonadiabatically(7,8). The XUV pulses with pulse durations of 950 attoseconds and 1.3 femtoseconds were characterized by an autocorrelation technique, based on two-photon above-threshold ionization(9) of helium atoms. Because of the small cross-section for above-threshold ionization(10), such an autocorrelation measurement of XUV pulses with photon energy larger than the ionization energy of helium has not hitherto been demonstrated(6,11-13). The technique can be extended to the characterization of higher harmonics at shorter wavelengths.