Advances in the generation of high-order harmonic of excited argon atoms in the State Key Laboratory of Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences have been made. Researchers in the use of argon excitation medium to achieve increased harmonic generation. In the experiment, the pump detection scheme (Fig. 1) was used. The pump light with a certain ellipticity excites some argon atoms from the ground state to the excited state, and the linearly polarized probe light drives to generate higher harmonics. Harmonic yield There is an enhanced platform area of ​​tens of picoseconds with the delay variation and the harmonic conversion efficiency is increased by nearly an order of magnitude compared to the probe light alone driving (FIG. 2). In addition, the fixed relative delay at 3ps (enhanced platform area) to change the pump light intensity and detect different gas pressure to enhance the life of the platform area, the experimental results and the corresponding theoretical simulation can be obtained: (1) Under the experimental conditions, The 3p + 4s state dominates the process. (2) Increasing the life of platform area is interpreted as the collisions between ionized electrons and excited atoms in the medium.
Attosecond pulses can be obtained by supercontinuum generation from higher harmonic processes, making it possible to track the movement of ultrafast electrons in physical, chemical and biological systems at such a short time scale, however, that applications are also faced with A second pulse produces a very low efficiency dilemma. At present, in order to improve the efficiency of the aconitic pulse generation, schemes such as two-color field and multi-color field, mixed gas medium and excited state medium are proposed one after another. However, there are few experiments on the generation of higher harmonics by the rare gas excited state medium.
The method is of great significance for improving the generation efficiency of high-order harmonics, obtaining high-brightness high-order harmonics and attosecond pulse light sources and further expanding the application range thereof. In addition, further studies on the higher harmonics generated by the excited state medium have important applications in the study of the excited-state electronic structure and the ultrafast electron-dynamic processes of atomic molecules. The research has been supported by the National 973 Program and the National Natural Science Foundation of China. Related work Posted by Appl. Phys. Lett. 107, 041110 (2015)
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