Optimal control of the orientation and alignment of an asymmetric-top molecule with terahertz and laser pulses

L. Coudert (1)

1 ISMO - Institut des Sciences Moléculaires d'Orsay

Quantum optimal control theory is applied to determine numerically the terahertz and nonres-onant laser pulses leading respectively to the highest degree of orientation and alignment of the asymmetric-top H2S molecule. The optimized terahertz pulses retrieved for temperatures of zero and 50 K lead after 50 ps to an orientation with ΦZx = 0.95973 and ΦZx = 0.74230, respectively. For the zero temperature, the orientation is close to its maximum theoretical value; for the higher temperature it is below. The mechanism by which the terahertz pulse populates high lying rotational levels is elucidated. The 5 ps long optimized laser pulse calculated for a zero temperature leads to an alignment with Φ 2 Zy = 0.94416 and consists of several kick pulses with a duration of ≈ 0.1 ps. It is found that the timing of these kick pulses is such that it leads to an increase of the rotational energy of the molecule. The optimized laser pulse retrieved for a temperature of 20 K is 6 ps long and yields a lower alignment with Φ 2 Zy = 0.71720.

Domaines: Physique [physics]; Physique Quantique [quant-ph]

L. Coudert. Optimal control of the orientation and alignment of an asymmetric-top molecule with terahertz and laser pulses. The Journal of Chemical Physics, 2018, 148 (9), pp.094306. ⟨10.1063/1.5018914⟩. ⟨hal-02371709⟩