该研究团队利用极紫外(XUV)脉冲，从理论上研究了延时红外激光对氦2s2p自电离态与2s2暗态共振耦合的阿秒瞬态吸收(ATA)光谱的影响。研究结果表明，在强成形XUV脉冲的作用下，2s2p态的产生过程中存在相消干涉，这导致不对称的2s2p费诺线形状在几十阿秒的时间延迟内可以很容易地调谐到对称的洛伦兹线形状。这种有效的控制相较于之前的实验中需要几十飞秒的调整时间有了显著的提升。
此外，研究人员还表明，在气体介质中传播后，可以通过实验观察到预测的ATA谱线形状。这一研究结果表明，强成形阿秒XUV脉冲在不到10阿秒的时间尺度上为控制和探测窄共振精细特征提供了可能性。
据悉，气体靶产生的高谐波在库珀极小值附近展现出明显的光谱特征和快速的相位变化。通过采用谱滤波技术，将脉冲在时域上分离成两个独立的脉冲，可以生成具有特定形状的孤立阿秒脉冲。
附：英文原文
Title: Controlling laser-dressed resonance line shape using attosecond extreme-ultraviolet pulse with a spectral minimum
Author: Fu, Yong, Wang, Bincheng, Wang, Kan, Tang, Xiangyu, Li, Baochang, Yin, Zhiming, Han, Jiaxin, Lin, C. D., Jin, Cheng
Issue&Volume: 2024-1-3
Abstract: High-harmonic generation from a gas target exhibits sharp spectral features and rapid phase variation near the Cooper minimum. By applying spectral filtering, shaped isolated attosecond pulses can be generated where the pulse is split into two in the time domain. Using such shaped extreme-ultraviolet (XUV) pulses, we theoretically study attosecond transient absorption (ATA) spectra of helium 2s2p autoionizing state which is resonantly coupled to the 2s2 dark state by a time-delayed infrared laser. Our simulations show that the asymmetric 2s2p Fano line shape can be readily tuned into symmetric Lorentzian within the time delay of a few tens of attoseconds. Such efficient control is due to the destructive interference in the generation of the 2s2p state when it is excited by a strongly shaped XUV pulse. This is to be compared to prior experiments where tuning the line shape of a Fano resonance would take tens of femtoseconds. We also show that the predicted ATA spectral line shape can be observed experimentally after propagation in a gas medium. Our results suggest that strongly shaped attosecond XUV pulses offer the opportunity for controlling and probing fine features of narrow resonances on the few-ten attoseconds timescale.
DOI: 10.1073/pnas.2307836121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2307836121