Abstract
We investigated molecular alignment wakes of femtosecond laser pulses. Evolution of nonadiabatic molecular alignment in nitrogen gas has been measured via its nonlinear interaction effects with a variably delayed probe pulse. The induced rotational wave packet was mapped as a function of the angular difference between polarization directions of femtosecond pump and probe pulses as well as their relative delay and the plot of the variations of the rotational wave packet, i.e. "quantum carpet", was found to be in good agreement with the calculated angular and temporal dependencies of molecular alignment parameter.
Highlights
When exposed to an intense and short femtosecond pulse, atomic and molecular media show highly nonlinear dynamics leading to phenomena such as high harmonic generation from filaments [1], long-range filament propagation [2], ultrashort pulse shaping and white-light generation [3, 4], as well as molecular alignment [5]
The experimental results of mapping rotational wave packets are compared with quantum mechanical calculations of the alignment parameter, and the results indicate that calculations describe all major experimentally observed features
Beyond understanding the dynamics of molecules interacting with ultrafast laser pulses, this information is applicable to any mechanism dependent on the molecular alignment
Summary
When exposed to an intense and short femtosecond pulse, atomic and molecular media show highly nonlinear dynamics leading to phenomena such as high harmonic generation from filaments [1], long-range filament propagation [2], ultrashort pulse shaping and white-light generation [3, 4], as well as molecular alignment [5]. The short laser pulse creates in each molecule a rotational wave packet, coherent superposition of the rotational states that will rephase and dephase in time after the laser pulse has ended. The intense probe pulse can experience self-focusing and spatially collapse due to the dynamic Kerr effect. This collapse stops when the intensity becomes high enough to generate free electrons and nonlinear losses tending to defocus the beam resulting in filamentary propagation [13]. The experimental results from mapping rotational wave packets are compared with quantum mechanically calculated angular and time dependencies of the molecular alignment parameter
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