Alignment of CS2 in intense nanosecond laser fields probed by pulsed gas electron diffraction

Abstract

A pulsed gas electron diffraction apparatus was developed and applied to investigate an alignment process of molecules in intense laser fields. A two-dimensional (2D) electron diffraction pattern of jet-cooled CS2 in intense nanosecond laser fields (1064 nm, ∼0.64 TW/cm2, 10 ns) was measured using short-pulsed 25 keV electron beam packets (∼7 ns) generated by irradiating a tantalum photocathode with the 4th harmonics of pulsed YAG laser light. The observed anisotropic 2D diffraction pattern was analyzed quantitatively by taking into account the spatio-temporal distributions of the laser pulses, the electron beam packets, and the molecular beam through a numerical simulation of the observed diffraction pattern. The anisotropy of the spatial distribution of molecular axes of CS2 in the laser polarization direction is accounted for by the effect of the intense laser fields. Considering the spatio-temporal averaging effect, the temporal pulse width of an electron packet required for real-time probing of the alignment process of molecules in intense nanosecond laser fields is discussed. A numerical simulation of temporal and spatial profiles of an electron packet is also performed to examine conditions for generating sub-picosecond ultrashort electron pulse for real-time probing of ultrafast molecular dynamics by the pulsed gas electron diffraction method.