Imaging of Coherent Molecular Rotation

Short laser pulses are widely used for controlling molecular rotational degrees of freedom and inducing molecular alignment, orientation, unidirectional rotation, and other types of coherent rotational motion. To follow the ultrafast rotational dynamics in real-time, several techniques for producing molecular movies have been proposed based on the Coulomb explosion of rotating molecules or recovering molecular orientation from the angular distribution of high harmonics. We offer and demonstrate a novel nondestructive optical method for direct visualization and recording movies of coherent rotational dynamics in molecular gas. The technique is based on imaging the time-dependent polarization dynamics of a probe light propagating through a gas of coherently rotating molecules. The probe pulse continues through a radial polarizer and is then recorded by a camera. The technique is illustrated by implementing it with two examples of time-resolved rotational dynamics: alignment–antialignment cycles in a molecular gas excited by a single linearly polarized laser pulse and unidirectional molecular rotation induced by a pulse with twisted polarization. This method may open new avenues in studies on fast chemical transformation phenomena and ultrafast molecular dynamics caused by strong laser fields of various complexities.

Optical imaging of spinning molecules. The images were captured by the camera during 3/4th revival. The polarization of the driving pulse describes a clockwise rotation in the image plane.

  1. J. Bert, E. Prost, I. Tutunnikov, P. Béjot, E. Hertz, F. Billard, B. Lavorel, U. Steinitz, I. Sh. Averbukh,
    and O. Faucher, “Optical Imaging of Coherent Molecular Rotors”, 
    Laser & Photonics Rev. 14(5), 1900344 (2020)

  2. I. Tutunnikov, E. Prost, U. Steinitz, P. Béjot, E. Hertz, F. Billard, O. Faucher, and I. Sh. Averbukh,
    “Visualizing coherent molecular rotation in a gaseous medium”, Phys. Rev. A 104, 053113 (2021)