Orientation of linear molecules in two-color laser fields with perpendicularly crossed polarizations

Je Hoi Mun, Hirofumi Sakai, and Rosario González-Férez

Phys. Rev. A 99, 053424 – Published 30 May 2019

Abstract

Molecular orientation methods based on nonresonant two-color laser pulses having parallel polarizations have been reported theoretically and experimentally. In this work, we demonstrate that perpendicularly polarized two-color laser fields can be used to achieve stronger molecular orientation when nanosecond laser pulses are used. The two-color fields align the molecules to the two-dimensional plane parallel to the field polarization; at the same time, they orient the molecules in the direction of the $2 ω$ polarization. We show that the interplay between the interactions due to the $ω$ - and $2 ω$ -laser fields provides stronger molecular orientation than the parallel field configuration. This is due to temporally synchronized generations of alignment and orientation, which reduce the nonadiabatic effects.

Received 19 February 2019

DOI:https://doi.org/10.1103/PhysRevA.99.053424

Physics Subject Headings (PhySH)

Coherent control

Atomic & molecular beams

Polarizability

Adiabatic approximation Dipole approximation First-principles calculations Perturbative methods Schroedinger equation

Atomic, Molecular & Optical

Authors & Affiliations

Je Hoi Mun^1,*, Hirofumi Sakai^2,3,†, and Rosario González-Férez^4,‡

¹Center for Relativistic Laser Science, Institute for Basic Science (IBS), Gwangju 61005, Republic of Korea
²Department of Physics, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
³Institute for Photon Science and Technology, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁴Instituto Carlos I de Física Teórica y Computacional, and Departamento de Física Atómica, Molecular y Nuclear, Universidad de Granada, 18071 Granada, Spain

^*mun1219@ibs.re.kr
^†hsakai@phys.s.u-tokyo.ac.jp
^‡rogonzal@ugr.es

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Issue

Vol. 99, Iss. 5 — May 2019

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Images

Figure 1
(a) Temporal evolutions of the electric-field components of parallel and perpendicularly polarized two-color laser fields during one optical cycle of the $ω$ -laser pulse. (b) A sketch (not to scale) of a triatomic linear molecule OCS and the Euler angles ( $θ$ , $ϕ$ ). The degree of orientation along the $Z$ axis, and the degrees of alignment along the $Z$ and $X$ axes are given by $〈 cos θ 〉$ , $〈 {cos}^{2} θ 〉$ , and $〈 {sin}^{2} θ {cos}^{2} ϕ 〉$ , respectively.
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Figure 2
For parallel fields, (a) and (b) show alignment and orientation Hamiltonians (6) and (7), respectively, as a function of the Euler angles in units of $π$ . For perpendicular fields, (c) and (d) show alignment and orientation Hamiltonians (9) and (10), respectively, as a function of the Euler angles in units of $π$ . The peak intensities are $I_{ω, 0} = 3.0 \times 10^{11}$ W/ ${cm}^{2}$ and $I_{2 ω, 0} = 10^{12}$ W/ ${cm}^{2}$ . The interaction potentials are expressed in units of Hz.
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Figure 3
For parallel fields, (a) orientation $〈 cos θ 〉$ and (b) alignment $〈 {cos}^{2} θ 〉$ as functions of time and of the peak intensity $I_{2 ω, 0}$ of the $2 ω$ -laser field computed by solving the time-dependent Schrödinger equation. The adiabatic results of the orientation and alignment are presented in (c) and (d), respectively. The peak intensity of the $ω$ -laser field is $I_{ω, 0} = 3 \times 10^{11} W / {cm}^{2}$ .
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Figure 4
For fixed peak intensities $I_{ω, 0} = 3 \times 10^{11} W / {cm}^{2}$ and $I_{2 ω, 0} = 5 \times 10^{11} W / {cm}^{2}$ , time evolutions of (a) orientation and (b) alignment, and (c) squares of the projections of the time-dependent wave function onto the adiabatic pendular states. The adiabatic results for the orientation and alignment, and temporal profiles of the two laser pulses are also plotted.
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Figure 5
For perpendicular fields, (a) orientation $〈 cos θ 〉$ , (b) alignment along the $Z$ -axis $〈 {cos}^{2} θ 〉$ , and (c) alignment along the $X$ -axis $〈 {sin}^{2} θ {cos}^{2} ϕ 〉$ as functions of time and of the peak intensity $I_{2 ω, 0}$ of the $2 ω$ -laser field computed by solving the time-dependent Schrödinger equation. The adiabatic results of the orientation along the $Z$ axis and the alignment along the $Z$ and $X$ axes are presented in (d), (e), and (f), respectively. The peak intensity of the $ω$ -laser field is $I_{ω, 0} = 3 \times 10^{11} W / {cm}^{2}$ . In the perpendicular configuration, either orientation along the $Z$ axis or alignment along the $X$ axis can be created depending on time and the relative intensities of the $ω$ - and $2 ω$ -laser pulses. The inset in (a) illustrates that the molecules are oriented (and aligned) along the $Z$ axis under the condition I marked in (a) and (b), where $t = 0$ ns and $I_{2 ω, 0} = 5 \times 10^{11} W / {cm}^{2}$ , while the inset in (c) illustrates that the molecules are aligned along the $X$ axis under the condition II marked in (c), where $t = 0$ ns and $I_{2 ω, 0} = 1.5 \times 10^{11} W / {cm}^{2}$ .
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Figure 6
For perpendicular fields and laser intensities $I_{ω, 0} = 3 \times 10^{11} W / {cm}^{2}$ and $I_{2 ω, 0} = 5 \times 10^{11} W / {cm}^{2}$ , time evolutions of (a) orientation, (b), (c) alignment along the $Z$ and $X$ axes, respectively, and (d) squares of the projections of the time-dependent wave function onto the adiabatic pendular states. The adiabatic results for the orientation and alignment and the temporal profiles of the two laser pulses are also plotted.
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