ECNU scientists make headway in molecules research


 Wu Jian

ON 13, February, a joint-research team led by ECNU scientist Wu Jian and Shanghai Jiao Tong University professor He Feng published an article titled High-order above-threshold dissociation of molecules, in the renowned journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

In the article, the scientists introduced a major breakthrough in experimentally probing and controlling ultrafast dynamics of electrons using waveform-controlled ultrashort laser pulses. It is the first time in 30 years for researchers to make such direct observations in this field of experimentation.

Furthermore, it was stated that electrons bound to atoms or molecules can simultaneously absorb multiple photons via the above-threshold ionization, with discrete peaks in the photoelectron spectrum; this is on account of the quantized nature of the light energy. Analogously, the above-threshold dissociation of molecules has been proposed to address the multiple-photon energy deposition in the nuclei of molecules.

This is a model from the published paper

In this case, it was predicted that nuclear energy spectra, consisting of photon-energy spaced peaks, exceed the binding energy of a molecular bond based on the fundamental laws of science.

The researchers report conclusive experimental observation of high-order above-threshold dissociation of H2 in strong laser fields where the tunneling-ionized electron transfers the absorbed multiphoton energy, which is above the ionization threshold to the nuclei via the field-driven inelastic rescattering. The results provide unequivocal evidence that the electron and nuclei of a molecule can absorb multiple photons, and thus above-threshold ionization and above-threshold dissociation must appear simultaneously, which is the cornerstone of molecular physics.

In 1979, Agostini et al observed the energy spectrum of electrons generated in 6-photon ionization of xenon atom with intense lasers. In his experiment, the measured kinetic-energy spectrum of the ejected electrons from xenon atoms showed an unusual shape that consists of a series of regularly spaced peaks that are separated by exactly the photon frequency of the incident laser field.

In 1990, A. Giusti-Suzor and some other scientists envisaged the incorporation of competitive ionization and dissociation in the theory.

Dr. Lu Peifen is the first author of the research paper while Prof. Wu Jian with the State Key Lab of Precision Spectroscopy, ECNU and Prof. He Feng with Shanghai Jiao Tong University are correspondent authors. The whole research project was presided by ECNU.

Prof. Wu, Dr. Lu (third one from the right) , and their research team members.

Wu and his group specialize in probing and controlling ultrafast dynamics of electrons in atoms and molecules that use waveform-controlled ultrashort laser pulses. Dr. Lu, a backbone in Wu’s research team, is a scholar who was introduced to the lab in 2015.

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East China Normal University