Controlling Molecular Rotation with Light

Aligning a sample of molecules with respect to defined axes in space has many applications ranging from chemical reaction dynamics to the control of high harmonics generation and attracts a lot of interest. Molecular rotation and thus alignment can be controlled by static electric fields or by optical fields. Our aim is the quantum dynamical description and control of field-free alignment which can be achieved with femtosecond laser pulses. Here, the laser field creates rotational wavepackets that show transient alignment after the end of the pulse. Due to the phenomenon of quantum revivals, the aligned rotational states periodically regain their angularly-squeezed shape. Rotational dynamics can be further controlled by applying sequences of laser pulses with different delay-times, intensities and polarization. Among the applications which we are pursuing are the enhancement of molecular alignment, excitation of uni-directional rotation and construction of molecular rotors, separation of nuclear spin isomers via spin-selective rotational dynamics and the control of internal torsion of non-rigid molecules.