Nonadiabatic laser-induced alignment of molecules: Reconstructing <cos(2) theta > directly from <cos(2) theta(2D)> by Fourier analysis

Anders Aspegren Sondergaard*, Benjamin Shepperson, Henrik Stapelfeldt

*Corresponding author af dette arbejde

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We present an efficient, noise-robust method based on Fourier analysis for reconstructing the three-dimensional measure of the alignment degree,〈cos 2Θ〉, directly from its two-dimensional counterpart, 〈cos 2Θ 2D〉. The method applies to nonadiabatic alignment of linear molecules induced by a linearly polarized, nonresonant laser pulse. Our theoretical analysis shows that the Fourier transform of the time-dependent 〈cos 2Θ 2D〉 trace over one molecular rotational period contains additional frequency components compared to the Fourier transform of 〈cos 2Θ〉. These additional frequency components can be identified and removed from the Fourier spectrum of 〈cos 2Θ 2D〉. By rescaling of the remaining frequency components, the Fourier spectrum of 〈cos 2Θ〉 is obtained and, finally, 〈cos 2Θ〉 is reconstructed through inverse Fourier transformation. The method allows the reconstruction of the 〈cos 2Θ〉 trace from a measured 〈cos 2Θ 2D〉 trace, which is the typical observable of many experiments, and thereby provides direct comparison to calculated 〈cos 2Θ〉 traces, which is the commonly used alignment metric in theoretical descriptions. We illustrate our method by applying it to the measurement of nonadiabatic alignment of I 2 molecules. In addition, we present an efficient algorithm for calculating the matrix elements of 〈cos 2Θ 2D〉 and any other observable in the symmetric top basis. These matrix elements are required in the rescaling step, and they allow for highly efficient numerical calculation of 〈cos 2Θ 2D〉 and 〈cos 2Θ〉 in general.

TidsskriftJournal of Chemical Physics
Antal sider10
StatusUdgivet - 7 jul. 2017


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