Inhibited rotational quenching in oriented ultra-high rotational states of CO2

Abstract

We demonstrate long-lived rotational orientation of CO2 molecules originally prepared in an optical centrifuge. The optical centrifuge traps molecules in a strong optical field and spins them to high rotational states by angular acceleration of the optical field. In the case of CO2, the optical centrifuge creates ultra-high rotational states with J ≥ 220. Polarisation-dependent, high-resolution transient infrared (IR) absorption was used to measure the spatial orientation of CO2 molecules in the (0000, J = 76) state following the optical centrifuge pulse and subsequent collisional energy transfer. Transient Doppler-broadened line profiles show that CO2 molecules in J = 76 probed with an IR transition dipole parallel to the initial plane of rotation are more plentiful and have higher translational temperatures than molecules with an IR transition dipole perpendicular to this plane. Time-dependent data show that the initial angular momentum orientation persists even after thousands of collisions, indicating that molecules in an optical centrifuge behave as quantum gyroscopes. These observations demonstrate that the optical centrifuge prepares an anisotropic rotational distribution and that molecules in oriented, ultra-high angular momentum states require many more collisions to randomise their orientation than do those in low rotational states.