Recently, Professor Ding Dajun’s research team of Institute of atomic and molecular physics of Jilin University has made important research progress in the field of ultrafast physics. The achievement, entitled "accurate in situ measurement of ellipticity based on subcycle ionization dynamics", was published online in Physical Review Letters on January 9, 2019.Jaha morrow and Donna Strickland won the 2018 Nobel Prize in physics for their pioneering contributions to the generation of ultra short laser pulses.There are three important parameters to describe the properties of Ultrafast Intense Laser, which are peak intensity, pulse width and degree of polarization.So far, the first two parameters can be measured accurately, but the measurement of the degree of polarization is far from meeting the needs of practical applications, especially there is no method to achieve real-time in-situ measurement of ellipticity.In close cooperation with Professor Peng Liangyou and academician Gong Qihuang of Peking University, the research team proposed a method to accurately measure the ellipticity of femtosecond elliptically polarized laser pulses in situ, which solved this key problem.In this method, two elliptically polarized light beams with the same other parameters but opposite rotation direction are used to ionize the noble gas xenon (Xe) atom. The electron suprathreshold ionization spectrum and the total yield spectrum of single ionized ion are sensitively dependent on the time delay between the two light pulses.Detailed experimental and theoretical studies show that the periodic modulation of energy spectrum and yield with time delay can accurately reflect the ratio between the minimum and maximum electric field intensity of elliptically polarized light in an optical period, so it can be used to accurately extract the ellipticity of each beam of elliptically polarized light.Especially for the case of high ellipticity, the accuracy of ordinary optical method is very limited, and the measurement method can still give accurate values.Through further theoretical simulation and analysis, this scheme can be widely used in a wide range of laser parameters.This study is a key step in characterizing the properties of Ultrafast Intense Laser Field accurately, and will play an important role in the quantitative and fine manipulation of important processes within atoms and molecules in the study of intense field physics.

Fig. 1 experimental setup and phase delay dependent suprathreshold ionization electron spectra obtained.

Associate Professor Wang Chuncheng and doctoral student Li Xiaokai from Institute of atomic and molecular physics of Jilin University and Xiao Xiangru, doctoral student of Peking University, are the co first authors of the paper. Professor Ding Dajun of Jilin University and Peng Liangyou of Peking University are the corresponding authors of the paper.The research has been supported by the national key R & D program and the National Natural Science Foundation of China. Associate Professor Wang Chuncheng is also supported by the Peiying project of Jilin University.

Link to the full text of the article:https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.013203