Isotope-selective molecular alignment induced by optimal laser pulses

ABSTRACT

Fluence-specified optimal control simulation is applied to C¹⁶O/C¹⁸O and ¹⁴N₂/¹⁵N₂ mixtures 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).

KEYWORDS:

• Molecular alignment
• laser control
• isotope
• isotopologue
• optimal control

Acknowledgments

The present study is dedicated to Professor André D. Bandrauk on the occasion of his 75th birthday. We are grateful to Professor H. Kono for stimulating discussions. YO acknowledges support in the form of a Grant-in-Aid for Scientific Research (C) (15K05373). This work was also supported by the Joint Usage/Research Program on Zero-Emission Energy Research, Institute of Advanced Energy, Kyoto University (ZE28B36).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Grant-in-Aid for Scientific Research (C) [grant number 15K05373]; Joint Usage/Research Program on Zero-Emission Energy Research, Institute of Advanced Energy, Kyoto University [grant number ZE28B36].