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Quantum rotational revivals
Quantum-mechanically, the laser pulse excites a wave packet which is formed from many rotational states.
From the equation above, one can clearly deduce the periodicity of the rotational wavepacket corresponding to the revival time it takes the evolving packet to reproduce itself, given by: Trev=1/(2Bc) where "B is the rotational constant and "c" is the speed of light. During its periodic evolution the wave packet exhibits several extreme angular distributions such as aligned (the molecules are transiently aligned along the laser polarization axis):
... and anti-aligned (the molecules lie in the plane perpendicular to the laser polarization):
The following cartoon plots the alignment factor as a function of delay between the pump pulse and the probing pulse.
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