Few-Cycle Laser Pulse Generation and Characterization for Coulomb Explosion Imaging of Molecules

Abstract

Ultrashort pulses can induce coulomb explosions of molecules through which ionic fragments receive substantial momentum. These momenta, measured in coincidence, carry information about the molecule's initial geometry. Momenta measurements can be done using a modified time-of-flight spectrometer. The spectrometer is improved upon by modifying the housing of its focusing mirror. The ion extraction field exhibited greater uniformity due to a more robust mirror mounting design and a correction of structural asymmetries. Ultrashort pulses are measurement tools, exploited for their brevity in duration and are sought to be made even shorter to improve their time resolution. Hollowfibre pulse compression studies are done to investigate the impacts of pressure on spectral broadening results. The pulses that exit the pulse stretching and compression components in the hollowfibre system can become riddled with distortions. The pulses need to be characterized to identify and correct distortions before they can be used to interrogate molecules. Frequency-resolved optical gating (FROG) techniques have demonstrated powerful characterization capabilities. A qualitative and quantitative methodology is presented in order to analyze the validity of FROG measurements of simple Gaussian pulses and then more complex, frequency modulated pulses.