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Ultrafast control of the dynamics of...

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Ultrafast control of the dynamics of diatomic molecules.

紀錄類型:	書目-語言資料,印刷品 : Monograph/item
正題名/作者:	Ultrafast control of the dynamics of diatomic molecules./
作者:	Pinkham, Daniel Walter.
面頁冊數:	159 p.
附註:	Adviser: Robert R. Jones.
Contained By:	Dissertation Abstracts International69-04B.
標題:	Physics, Atomic. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3312118
ISBN:	9780549599142

Ultrafast control of the dynamics of diatomic molecules.
Pinkham, Daniel Walter.

Ultrafast control of the dynamics of diatomic molecules. - 159 p.

Adviser: Robert R. Jones.

Thesis (Ph.D.)--University of Virginia, 2008.

Samples of gaseous diatomic molecules are excited into rotational wavepackets by ultrashort laser pulses, and the resultant dynamics are probed in the time-domain. The preparation of non-isotropic rotational distributions of molecules in field-free conditions enables a number of strong-field physics experiments to be performed. This process, known as transient alignment, serves as the central tool for most of the work described here. First, the angle-dependent ionization rates are measured for samples of room-temperature CO. Next, the polarizability anisotropy Deltaalpha---quantity indicating how easily the electronic cloud is distorted by an applied electric field---is extracted for HBr molecules at &sim;30 K, by observing the transient alignment efficiency in comparison to that of a reference molecule, N2. In a follow-up experiment, a feedback-optimized algorithm is used to improve the transient alignment process by phase-shaping the pump laser pulses, and principal control analysis is used to search for pulse-shaping parameter "knobs" that most effectively control the alignment process. We observe that a rigid-rotor model with a constant Deltaalpha is sufficient to describe the alignment dynamics. In the final section, we explore asymmetric dissociation of multiply charged ions produced by intense laser ionization in a 2-color field. By combining 800 nm and 400 nm laser pulses we produce an oscillating electric field with a controllable, periodic "up-down" asymmetry in the lab frame. This asymmetry can be used to control the relative yields of ion fragments ejected in different directions. In contrast to previous studies with 2-color fields, we utilize an independent, symmetric, ionization pulse to determine that the observed dissociation is the result of an induced directionality in the field-dressed molecules rather than transient orientation of the molecule. This asymmetry is found to be an effect of enhanced molecular ionization at a critical internuclear distance (RC > Req). This fact is further illustrated by our observation of an asymmetry in the dissociation of symmetric molecules (e.g. N3+2 → N2+ + N+). We conclude with an analysis of transient molecular orientation in 2-color fields and describe preliminary attempts to observe it.

ISBN: 9780549599142Subjects--Topical Terms:

1029235
Physics, Atomic.

Ultrafast control of the dynamics of diatomic molecules.
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502 $a Thesis (Ph.D.)--University of Virginia, 2008.
520 $a Samples of gaseous diatomic molecules are excited into rotational wavepackets by ultrashort laser pulses, and the resultant dynamics are probed in the time-domain. The preparation of non-isotropic rotational distributions of molecules in field-free conditions enables a number of strong-field physics experiments to be performed. This process, known as transient alignment, serves as the central tool for most of the work described here. First, the angle-dependent ionization rates are measured for samples of room-temperature CO. Next, the polarizability anisotropy Deltaalpha---quantity indicating how easily the electronic cloud is distorted by an applied electric field---is extracted for HBr molecules at &sim;30 K, by observing the transient alignment efficiency in comparison to that of a reference molecule, N2. In a follow-up experiment, a feedback-optimized algorithm is used to improve the transient alignment process by phase-shaping the pump laser pulses, and principal control analysis is used to search for pulse-shaping parameter "knobs" that most effectively control the alignment process. We observe that a rigid-rotor model with a constant Deltaalpha is sufficient to describe the alignment dynamics. In the final section, we explore asymmetric dissociation of multiply charged ions produced by intense laser ionization in a 2-color field. By combining 800 nm and 400 nm laser pulses we produce an oscillating electric field with a controllable, periodic "up-down" asymmetry in the lab frame. This asymmetry can be used to control the relative yields of ion fragments ejected in different directions. In contrast to previous studies with 2-color fields, we utilize an independent, symmetric, ionization pulse to determine that the observed dissociation is the result of an induced directionality in the field-dressed molecules rather than transient orientation of the molecule. This asymmetry is found to be an effect of enhanced molecular ionization at a critical internuclear distance (RC > Req). This fact is further illustrated by our observation of an asymmetry in the dissociation of symmetric molecules (e.g. N3+2 → N2+ + N+). We conclude with an analysis of transient molecular orientation in 2-color fields and describe preliminary attempts to observe it.
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