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Published online: 5 August 2009 | Corrected online: 5 August 2009 | doi:10.1038/nchina.2009.159

Molecular physics: A few kicks in the right direction

Felix Cheung

Introduction

© (2009) APS

Having the ability to control the orientation of gas molecules is essential to understanding dynamics in many chemical reactions. In recent years, scientists have developed numerous techniques for controlling molecular orientation, but most have involved intense laser fields, which can modify the physics and chemistry of the gas molecules undesirably. Shulin Cong and co-workers at Dalian University of Technology¹ have now come up with a 'field-free' strategy for controlling molecular orientation.

The strategy involves the use of few-cycle terahertz pulses to 'kick' the gas molecules into place. The kick causes each gas molecule to rotate faster or slower depending on the molecular orientation and motion at the time of the kick. After a few kicks, the gas molecules all become aligned in the same direction.

To demonstrate the efficiency and robustness of the strategy, the researchers performed numerical calculations for lithium hydride (LiH), a molecule for which accurate data is available. Their calculations showed that efficient field-free molecular orientation can be achieved even for LiH molecules with high rotational energies (top and bottom pictures show wave-packet images of LiH before and after molecular orientation). Moreover, the researchers found a simple dependence between the degree of orientation and the carrier-envelope phase (CEP) of the terahertz pulses, suggesting that CEP is an important parameter for controlling molecular orientation.

The researchers believe that their strategy is experimentally viable because few-cycle terahertz pulse technology is already available as a research tool.

The authors of this work are from:
Department of Physics, Dalian University of Technology, Dalian, China.

Reference

1. Shu, C. C., Yuan, K. J., Hu, W. H. & Cong, S. L. Carrier-envelope phase-dependent field-free molecular orientation. Phys. Rev. A 80, 011401 (2009). | Article |