In cooperation with Peking University, professor Wang Chuncheng from IAMP  has made new progress in accurate in situ measurement of ellipticity based on subcycle ionization dynamics. The results were published in PHYSICAL REVIEW LETTERS on January 9, 2019. Elliptically polarized laser pulses (EPLPs) are widely applied in many fields of ultrafast sciences, but the ellipticity (ε) has never been in situ measured in the interaction zone of the laser focus. In this Letter, we propose and realize a robust scheme to retrieve the ε by temporally overlapping two identical counterrotating EPLPs. The combined linearly electric field is coherently controlled to ionize Xe atoms by varying the phase delay between the two EPLPs. The electron spectra of the above-threshold ionization and the ion yield are sensitively modulated by the phase delay. They demonstrate that these modulations can be used to accurately determine ε of the EPLP. We show that the present method is highly reliable and is applicable in a wide range of laser parameters. The accurate retrieval of ε offers a better characterization of a laser pulse, promising a more delicate and quantitative control of the subcycle dynamics in many strong field processes.

The co-first authors of this study are professor Wang, Dr. Li Xiaokai  from the IAMP and professor Xiao Xiangru  from Peking University.  The corresponding authors of this study are professor Ding Dajun from the institute and  professor Peng Youliang from Peking University.

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