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The rotation-translation thermalization of C02 gas is investigated 500 ps after its preheating by a nonresonant short and intense laser pulse. The temperature of thermalization is optically determined with two additional short laser pulses enabling a field-free molecular alignment process and its probing, respectively. The measurements are performed for various intensities of the preheat pulse, leading to the observation of different temperatures which are in very good agreement with classical molecular dynamics simulations. The results can be regarded as a step towards real-time tracking of ultrafast relaxation pathways in molecular motion [ABSTRACT FROM AUTHOR]

We study the triggering of single filaments due to turbulence in the beam path for a laser of power below the filamenting threshold. Turbulence can act as a switch between the beam not filamenting and producing single filaments. This positive effect of turbulence on the filament probability, combined with our observation of off-axis filaments, suggests the underlying mechanism is modulation instability caused by transverse perturbations. We hereby experimentally explore the interaction of modulation instability and turbulence, commonly associated with multiple filaments, in the single-filament regime. [ABSTRACT FROM AUTHOR]