Observation of Chemical Reaction in Intense Laser Fields by Ultra-short Pulsed Electron Diffraction

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In this research project, ultra-short electron pulses were generated and dynamical behavior of molecules in intense laser fields was investigated. Our achievements are summarized as follows.(1)A molecular alignment process of CS_2 in an intense ns laser field (0.64 TW/cm^2) was observed as an anisotropic 2D diffraction image by ns pulsed electron diffraction measurements. From the analysis of the obtained anisotropic image, <<cos^2θ>> = 0.36 was derived as a spatio-temporal averaged value. The extent of the alignment was interpreted theoretically by taking into account the rotational temperature, T_R=10 K, and the polarizabilities of CS_2.(2)A high-sensitive detection system, equipped with an image intensifier detector and a cooled slow-scan CCD camera, achieve high sensitive detection of scattered electrons. The weak diffraction signals measured by picosecond electron pulses (the number of electrons per pulse ≦ 10^4) were detected with a high signal-to-noise ratio using this new detection system.(3)The ultrafast structural deformation of CS_2 in an intense ns laser field (〜10^<12> W/cm^2) was probed by the ps electron diffraction method. It was interpreted that this structural change reflects the nuclear dynamics on the dressed potential energy surface formed by the light-induced strong coupling among the electronic states of CS_2 in an intense laser field.(4)A numerical simulation of generation and propagation of electron packets was performed to examine the conditions required for the generation of ultra-short (〜 1 ps) electron pulses. It was found that ultrashort electron pulses whose temporal width is shorter than 1 ps could be generated when the number of electrons is below 10^3.