Ultrafast Laser Induced Molecular Alignment and Deformation:  Experimental Evidence from Neutral Molecules and from Fragment Ions

Abstract

The alignment and molecular structure deformations induced by intense off-resonance excitation with ultrafast laser pulses are examined using femtosecond transient grating spectroscopy and by angle resolved multiphoton ionization in a molecular beam. The goal of this study is to correlate evidence obtained from the angular dependence of multiphoton ionization and from rotational recurrences observed in neutral molecules regarding alignment and molecular structure deformation. Structural parameters are determined by analysis of the fieldfree rotational recurrences, obtained by transient grating measurements, or by analysis of the anisotropy in the detected fragment ions, in the molecular beam experiments. Experimental data were obtained for CS 2 , CO 2 , acetylene, and benzene, for pulse intensities ranging from 10 11 to 10 14 W/cm 2 . The experimental results are consistent with molecular alignment resulting from a "kick" induced by the ultrafast off-resonance field. The results also provide evidence of molecular structure deformations. Results from transient grating experiments indicate that the electric field can induce alignment and bending in polyatomic molecules and that these effects can take place in the absence of ionization.

A Stark Future for Quantum Control

“…[123][124][125] A third approach to the generation of alignment, known as the switched wavepacket (SWP) method, is effectively a hybrid of the adiabatic and kicked approaches. This strategy utilizes an intense laser field that undergoes a slow (adiabatic) rise to generate alignment, followed by a rapid (diabatic) switch-off that induces subsequent rotational revivals under field-free conditions.…”

Suppression of plasma contribution in femtosecond degenerate four‐wave mixing (fs‐DFWM) at high intensity

“…Transients grating or degenerate four-wave mixing (DFWM) experiments can be also performed to explore molecular alignment. [7][8][9] In these experiments, two synchronized crossed pump pulses create a transient grating which diffracts light from a third probe time delayed pulse. The DFWM signal reflects also post-pulse molecular alignment manifested by periodic transients.…”

Изменение Нормальных Координат И Геометрических Параметров Молекулы В Лазерном Поле

“…Отметим, что взаимодействие лазерного излуче-ния с пространственно-ориентированными молекулами исследуется экспериментально во многих работах (см., например, [28][29][30][31]). Изменение геометрических параметров в многоатом-ных молекулах наблюдалось при изучении кулоновского взрыва (см., например, [32][33][34][35][36][37][38][39][40]). Такое изменение со-провождается в общем случае изменением нормальных координат, определяющих положения ядер атомов, вхо-дящих в состав молекулы.…”

“…Изменение геометрических параметров в многоатом-ных молекулах наблюдалось при изучении кулоновского взрыва (см., например, [32][33][34][35][36][37][38][39][40]). Такое изменение со-провождается в общем случае изменением нормальных координат, определяющих положения ядер атомов, вхо-дящих в состав молекулы.…”