为了获得能量范围在水窗区间的高强度光谱连续区,提出了一种利用啁啾调 频场调控激光波形的方法。研究发现:在单色多周期负向啁啾调频场驱动下, 谐波截止能量可以得到延伸。当引入第二束负向啁啾激光场时,不仅谐波截止能量延伸到水窗区间,而且谐波辐射强 度有近3个数量级的提高。当引入第三束123 nm紫外激光场时,在紫外共振电离的影响下,谐波辐射强度进一步增强。 谐波强度增强与第三束激光场啁啾参数和激光相位几乎无关。最后,通过叠加水窗区间光谱的谐波可获 得脉宽为38 as的单个阿秒脉冲。

In order to obtain high-intensity water window spectral continuum, a method to control the laser waveform by using frequency-chirp field is proposed. It is found that the harmonic cutoff can be extended in the presence of single-color multi-cycle negative chirped pulse. With the introduction of the second negative chirped pulse, not only the harmonic cutoff can be extended to the water window region, but also the harmonic yield can be enhanced by nearly three orders of magnitudes. When the third 123 nm ultraviolet pulse is added, the harmonic yield can be further improved due to ultraviolet resonance ionization, and the enhancement of harmonic yield is nearly independent of the chirp and laser phase of the third pulse. Finally, with the superposition of the harmonics on the water window spectral continuum, a 38 as pulse can be obtained.