Coherent rotational/vibrational excitation by intense ultrashort laser pulses

Yasuhiro Ohshima
Event Date and Time: 
Mon, 2012-04-30 02:30 - 03:30
Chem D-215
Local Contact: 
Taka Momose
Intended Audience: 

When a gaseous molecular sample is irradiated by an intense nonresonant ultrashort laser pulse, the laser field exerts a torque that aligns the molecular axis along the laser polarization vector, due to the interaction with the molecular anisotropic polarizability.  Here the field–molecule interaction only remains in much shorter duration than the characteristic time for molecular rotation, and thus the rotation of the molecules is coherently excited to create a rotational quantum wave packet (WP).  We have developed a method to explore the nonadiabatic excitation in a quantum-state resolved manner and applied it to diatomic and symmetric-top molecules [1].  It has been shown that the state distribution is a useful experimental source for verifying the excitation process [2,3].  When a pair of excitation pulses is implemented with appropriate time delay between them, partial control of rotational- state distribution has been achieved [1,4].  In a favorable case, the double-pulse excitation coupled with the state-selective probe has enabled us to reconstruct experimentally a rotational WP thus created [5].  If the mutual polarization direction and time delay between the two pulses are adjusted, the sense of rotation around the laser propagation direction can also be controlled, yielding to a rotational WP exhibiting angular-momentum orientation [6].

Nonadiabatic interaction with a nonresonant intense ultrashort laser field can also coherently excite vibration of molecule through the structural dependence of the molecular polarizability.  We have recently succeeded in creating and observing WPs pertinent to intermolecular vibrations of several molecular clusters in their electronic ground states.  The present study is a keystone toward real-time conformational control of flexible molecules.



(1) Y. Ohshima and H. Hasegawa, Int. Rev. Chem. Phys. 29, 619 (2010).  (2) H. Hasegawa and Y. Ohshima, Phys. Rev. A 74, 061401(R) (2006).  (3) H. Hasegawa and Y. Ohshima, Chem. Phys. Lett. 454, 148 (2008).  (4) D. Baek, H. Hasegawa, and Y. Ohshima, J. Chem. Phys. 134, 224302 (2011).  (5) H. Hasegawa and Y. Ohshima, Phys. Rev. Lett. 101, 053002 (2008).  (6) K. Kitano, H. Hasegawa, and Y. Ohshima, Phys. Rev. Lett. 103, 223003 (2009).

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