Isotope-selective molecular alignment induced by optimal laser pulses.

Fluence-specified optimal control simulation is applied to C16O/C18O and14N2/15N2mixtures to numerically design laser pulses that best achieve isotope-selective alignment. The degree of control is measured in terms of selectivity, which is defined by the difference in the degree of alignment between a heavy isotopologue (HI) and a light isotopologue (LI). Optimal pulses are composed of several subpulses that cooperate with the so-called revivals of the rotational wave packets. Although the two mixtures have slightly different molecular parameters and isotope shifts, it turns out that the optimal pulses share common multi-pulse structures. We also develop a pulse-partitioning analysis to quantitatively and systematically examine the role of inter-subpulse cooperation in the improvement of the isotope-selective alignment. According to the analyses, we find that the ‘coherent’ and the ‘incoherent’ inter-subpulse cooperation almost equally contribute to the improvement of the degree of alignment (HI) as well as that of anti-alignment (LI). [ABSTRACT FROM AUTHOR]