中国物理B ›› 2009, Vol. 18 ›› Issue (9): 3850-3855.doi: 10.1088/1674-1056/18/9/039

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Role of highest occupied molecular orbitals in molecular field-free alignment by a femtosecond pulse

陈德应, 王玉铨, 夏元钦, 樊荣伟, 张盛   

  1. National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China
  • 收稿日期:2008-11-12 修回日期:2008-12-23 出版日期:2009-09-20 发布日期:2009-09-20
  • 基金资助:
    Project supported by the Program of Excellent Team in Harbin Institute of Technology, the Program for New Century Excellent Talents in University (NCET), and National Natural Science Foundation of China (Grant Nos 10774033, 60878018 and 10674036).

Role of highest occupied molecular orbitals in molecular field-free alignment by a femtosecond pulse

Chen De-Ying(陈德应), Wang Yu-Quan(王玉铨)†ger, Xia Yuan-Qin(夏元钦), Fan Rong-Wei(樊荣伟), and Zhang Sheng(张盛)   

  1. National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China
  • Received:2008-11-12 Revised:2008-12-23 Online:2009-09-20 Published:2009-09-20
  • Supported by:
    Project supported by the Program of Excellent Team in Harbin Institute of Technology, the Program for New Century Excellent Talents in University (NCET), and National Natural Science Foundation of China (Grant Nos 10774033, 60878018 and 10674036).

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摘要： This paper studies the molecular rotational excitation and field-free spatial alignment in a nonresonant intense laser field numerically and analytically by using the time-dependent Schr?dinger equation. The broad rotational wave packets excited by the femtosecond pulse are defined in conjugate angle space, and their coefficients are obtained by solving a set of coupled linear equations. Both single molecule orientation angles and an ensemble of O2 and CO molecule angular distributions are calculated in detail. The numerical results show that, for single molecule highest occupied molecular orbital (HOMO) symmetry σ tends to have a molecular orientation along the laser polarization direction and the permanent dipole moment diminishes the mean of the orientation angles; for an ensemble of molecules, angular distributions provide more complex and additional information at times where there are no revivals in the single molecule plot. In particular, at the revival peak instant, with the increase of temperature of the molecular ensemble, the anisotropic angular distributions with respect to the laser polarization direction of the π g orbital gradually transform to the symmetrical distributions regarding the laser polarization vector and for two HOMO configurations angular distributions of all directions are confined within a smaller angle when the temperature of the molecular ensemble is higher.

Abstract: This paper studies the molecular rotational excitation and field-free spatial alignment in a nonresonant intense laser field numerically and analytically by using the time-dependent Schr?dinger equation. The broad rotational wave packets excited by the femtosecond pulse are defined in conjugate angle space, and their coefficients are obtained by solving a set of coupled linear equations. Both single molecule orientation angles and an ensemble of O2 and CO molecule angular distributions are calculated in detail. The numerical results show that, for single molecule highest occupied molecular orbital (HOMO) symmetry $\sigma$ tends to have a molecular orientation along the laser polarization direction and the permanent dipole moment diminishes the mean of the orientation angles; for an ensemble of molecules, angular distributions provide more complex and additional information at times where there are no revivals in the single molecule plot. In particular, at the revival peak instant, with the increase of temperature of the molecular ensemble, the anisotropic angular distributions with respect to the laser polarization direction of the $\pi$g orbital gradually transform to the symmetrical distributions regarding the laser polarization vector and for two HOMO configurations angular distributions of all directions are confined within a smaller angle when the temperature of the molecular ensemble is higher.

Key words: molecular field-free alignment, highest occupied molecular orbital, angular distribution, femtosecond pulse

中图分类号:  (Rotational analysis)

  • 33.20.Sn
31.15.-p (Calculations and mathematical techniques in atomic and molecular physics) 33.15.Kr (Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility) 33.15.Mt (Rotation, vibration, and vibration-rotation constants) 42.60.Jf (Beam characteristics: profile, intensity, and power; spatial pattern formation) 42.65.Re (Ultrafast processes; optical pulse generation and pulse compression)