We investigated the ultrafast proton migration and the Coulomb explosion (CE) dynamics of methyl chloride (CHCl) in intense femtosecond laser fields at the wavelengths of 800 nm (5.5 × 10 W/cm) and 400 nm (4 × 10 W/cm), respectively. Various fragment channels from molecular dication and trication were observed by coincidence momentum imaging through the measurement of their kinetic energy releases (KERs). The proton migration from different charged parent ions was analyzed from the obtained KER distributions. For the direct CE channel of CH + Cl and CH + Cl, the contribution of multiply excited electronic states and multicharged states is identified. In addition, the measurements of relative yields of the fragmentation channel at different laser wavelengths provide a selective control of proton migration for CHCl molecules in intense laser fields.

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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 work, we propose and realize a robust scheme to retrieve the ε by temporally overlapping two identical counter-rotating 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. We 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 sub-cycle dynamics in many strong field processes. arXiv:1812.07309v1 [physics.atom-ph]

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