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

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We present an efficient, noise-robust method based on Fourier analysis for reconstructing the threedimensional measure of the alignment degree, <cos(2) theta > directly from its two-dimensional counterpart, <cos(2) theta(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(2)theta(2D)> trace over one molecular rotational period contains additional frequency components compared to the Fourier transform of <cos(2) theta > These additional frequency components can be identified and removed from the Fourier spectrum of <cos(2) theta(2D)> By rescaling of the remaining frequency components, the Fourier spectrum of h <cos(2) theta > is obtained and, finally, <cos(2) theta > is reconstructed through inverse Fourier transformation. The method allows the reconstruction of the <cos(2) theta > trace from a measured <cos(2) theta(2D)> trace, which is the typical observable of many experiments, and thereby provides direct comparison to calculated <cos(2) theta > 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(2)theta(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(2) theta(2D)> and <cos(2) theta > in general.

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

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