分子体系温度和入射激光能量对O_2分子取向影响的物理机制

The physical mechanism of the effects of temperature and pulse energy of laser on the alignment of O_2

从形成分子转动波包的过程中,参与转动跃迁的分子转动态布居情况出发,理论上详细地研究了单脉冲分子取向中,分子体系温度和入射激光能量对O2分子体系取向的影响.结果表明:增加分子体系的转动温度,会使参与转动跃迁的转动能级数目增加,但是与此同时,各个转动态的参与几率却大幅度的下降.而增加激光能量也会使参与转动跃迁的分子转动能级数目增加,但不同于增加分子温度的是,这时候参与转动跃迁的各个分子转动能级的参与几率并没有降低.因此,增加分子的转动温度和增加激光脉冲的能量都会增加分子参与转动跃迁的能级数目,但增加分子的转动温度会降低分子的取向度,而增加激光脉冲的能量(小于分子电离的激光能量)会增加分子的取向度.

In this paper the effects of temperature and pulse energy of laser on the alignment of O_2 have been studied theoretically by analyzing the populating of molecular rotational states in molecular alignment. In this process,randomly distributed molecules will form a molecular rotational wavepacket through the interaction between laser pulse and molecules and molecular rotational transition. The results are going as follows: the rational levels which participate in rotational transition will increase when the temperature of molecular system increases. But at the same time the transition probability at all rotational levels will be sharply reduced. When we increase the pulse energy of laser,the rational levels which participate in rotational transition also increase. However,the transition probability at all rotational levels will not decline in this case. Therefore,the increase in temperature and pulse energy of laser will both increase the rational levels which participate in rotational transition. But temperature increase will weaken the molecular alignment while the increase of pulse energy of laser will strengthen the molecular alignment.