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Femtosecond Filament Interaction as a Probe for Molecular Alignment

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Technical Report

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University of Central Florida Orlando United States

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Femtosecond laser filamentation is a highly nonlinear propagation mode. When a laser beam propagates with a peak power exceeding a critical value Pcr 5 GW at 800 nm in air, the Kerr effect tends to collapse the beam until the intensity is high enough to ionize the medium, giving rise to plasma defocusing. A dynamic competition between these two effects takes place leaving a thin and weakly ionized plasma channel in the trail of the pulse. When an ultrafast laser pulse interacts with molecules, it will kick them, spinning them about their axis of the polarization. As the quantum rotational wave packets interact, the molecules will experience periodic field-free alignment. Recent work has demonstrated the effect of molecular alignment on laser filamentation of ultra-short pulses. Revival of the molecular alignment can modify filamentation parameters as it can locally increase or decrease the refractive index. In this thesis, we demonstrate with simulations and experiments that these changes in the filament parameters collapse distance and filament plasma length can be used to probe molecular alignment in CO2.

Subject Categories:

  • Lasers and Masers
  • Electricity and Magnetism
  • Optics

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