Direct observation of molecular alignment in an intense laser field by pulsed gas electron diffraction I: observation of anisotropic diffraction image

The anisotropic two-dimensional (2D) electron diffraction pattern of jet-cooled CS2 in an intense nanosecond Nd:YAG laser field (1064 nm, ∼0.64 TW/cm2, 10 ns) was measured by a short-pulsed 25 keV electron beam packet (∼7 ns) generated by irradiating a tantalum photocathode with the fourth harmonics of another nanosecond pulsed YAG laser radiation. The observed anisotropic 2D diffraction pattern is reproduced by simulation, in which the alignment of the S–C–S molecular axis along the laser polarization direction is taken into account. The results indicate that the molecular alignment process in an intense laser field can be probed directly by the pulsed gas electron diffraction method.