Qiao Yue, Wang Xinyu, Li Xuefeng, Wu Linyan, Yu Ruixian, Guo Fuming, Wang Jun, Chen Jigen, Yang Yujun
Opt Express. 2023 Oct 23;31(22):36327-36336. doi: 10.1364/OE.503528.
Efficient enhancement of harmonic brightness near the cutoff region is achieved by employing laser pulses with a small positive chirp in theory, where the laser intensity and frequency near the peak of the laser pulse are almost unchanged relative to the chirp-free field. The improvement of harmonic brightness is achieved under the condition that the ionization probability is almost unchanged. Through the analysis of the harmonics contributed by the rising and falling parts of the laser pulse, we have uncovered a "frequency compensation" mechanism that leads to an enhanced harmonic brightness near the cutoff region. Under appropriate chirp parameters, the harmonics contributed by the rising and falling parts can be constructively interfered in a smaller frequency range with greater intensity, thereby obtaining harmonics with good monochromaticity and high brightness. This study explains the mechanism of harmonic brightness enhancement from a new perspective, and provides a new idea for harmonic regulation without changing the ionization.
理论上，通过使用具有小正啁啾的激光脉冲，可以在截止区域附近有效地增强谐波亮度，其中激光脉冲峰值附近的激光强度和频率相对于无啁啾场几乎不变。在电离概率几乎不变的条件下实现了谐波亮度的提高。通过分析激光脉冲上升和下降部分贡献的谐波，我们发现了一种“频率补偿”机制，该机制导致截止区域附近的谐波亮度增强。在适当的啁啾参数下，上升和下降部分贡献的谐波可以在较小的频率范围内以更大的强度进行相长干涉，从而获得具有良好单色性和高亮度的谐波。本研究从一个新的角度解释了谐波亮度增强的机制，并为在不改变电离的情况下进行谐波调控提供了新的思路。
