High harmonic generation driven by mid-infrared lasers*

In recent years, high-power ultrafast lasers centered at 1.7 to 2.5 micron have enabled the generation of attosecond X-ray pulses reaching the water window (282 to 533 eV), which is of great interest given their applications in the study of electron dynamics in atoms, molecules and condensed matter containing carbon, nitrogen, oxygen and other important elements [1]. X-ray pulses as short as 53 attoseconds have been demonstrated at the carbon K-edge. Novel spectral phase retrieval schemes such as neural network have been implemented to attosecond streaking techniques for faster and more reliable characterization of X-ray pulses. The water window X-ray sources have been applied to attosecond transient absorption spectroscopy with element specificity and sub-optical-cycle temporal resolution [2].

References:
1. Jie Li, Jian Lu, Andrew Chew, Seunghwoi Han, Jialin Li, Yi Wu, He Wang, Shambhu Ghimire, Zenghu Chang, “Attosecond Science based on High Harmonic Generation from Gases and Solids,” Nature Communications 11, 2748 (2020).
2. Nariyuki Saito, Hiroki Sannohe, Nobuhisa Ishii, Teruto Kanai, Nobuhiro Kosugi, Yi Wu, Andrew Chew, Seunghwoi Han, Zenghu Chang, and Jiro Itatani, “Real-time observation of electronic, vibrational, and rotational dynamics in nitric oxide with attosecond soft X-ray pulses,” Optica 6, 1542 (2019).