Impulsive orientation of symmetric-top molecules excited by two-color femtosecond pulses is considered. In addition to the well-known transient orientation appearing immediately after the pulse and then reemerging periodically due to quantum revivals, we report the phenomenon of field-free long-lasting orientation. Long-lasting means that the time averaged orientation remains non-zero until destroyed by other physical effects, e.g. intermolecular collisions. The effect is caused by the combined action of the field-polarizability and field-hyperpolarizability interactions. The dependence of degree of long-lasting orientation on temperature and pulse's parameters is considered. The effect can be measured by means of second (or higher-order) harmonic generation, and may be used to control the deflection of molecules traveling through inhomogeneous electrostatic fields.

中文翻译：

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双色飞秒脉冲激发对称顶分子的持久定向

考虑了由双色飞秒脉冲激发的对称顶部分子的脉冲取向。除了众所周知的瞬态取向在脉冲后立即出现然后由于量子复兴而周期性地重新出现之外，我们还报告了无场持久取向的现象。持久意味着时间平均取向保持非零，直到被其他物理效应破坏，例如分子间碰撞。该效应是由场极化率和场超极化率相互作用的联合作用引起的。考虑了持久定向程度对温度和脉冲参数的依赖性。可以通过二次（或更高阶）谐波产生来测量效果，