Photoexcitation of atoms by cylindrically polarized Laguerre-Gaussian beams

Abstract

We analyze the photo-excitation of atoms with a single valence electron by cylindrically polarized Laguerre-Gaussian beams. Theoretical analysis is performed within the framework of first-order perturbation theory and by expanding the vector potential of the Laguerre-Gaussian beam in terms of its multipole components. For cylindrically polarized Laguerre-Gaussian beams, we show that the (magnetic) sub-components of electric-quadrupole field vary significantly in the beam cross-section with beam waist and radial distance from the beam axis. We discuss the influence of varying magnetic multipole component in the beam cross-section on the sub-level population of a localized atomic target. In addition, we calculate the total excitation rate of electric quadrupole transition ($4s \;^{2}S_{1/2} \rightarrow 3d \;^{2}D_{5/2}$) in a mesoscopic target of Ca$^{+}$ ion. These calculations shows that the total rate of excitation is sensitive to the beam waist and the distance between center of the target and the beam axis. However, the excitation by cylindrically polarized Laguerre-Gaussian beam is found more efficient in driving electric quadrupole transition in the mesoscopic atomic target than the circularly polarized beams.