参量匹配对双色双共振多光子电离几率的影响

Influence of laser parameters matching on double-color double-resonance multiphoton ionization probability

以寻求提高共振增强多光子电离(REMPI)几率的物理参量为研究目的,采用光和物质相互作用的密度矩阵方程理论,数值模拟了双色双共振多光子电离过程中泵浦和探测光的参量匹配对电离几率的影响。结果发现,一定条件下,提高电离几率的最佳匹配条件是:1)两束激光强度、脉冲宽度均相等且取值较大;2)两束激光无相对延迟,输出频率和相应激发跃迁共振。对1+1+1经探测光双光子共振吸收电离过程,电离几率对探测光更敏感。实际应用中,若不能保证最佳匹配条件的实现,应尽量提高探测光的强度、脉冲宽度及近共振吸收;若实验条件不能实现激光频率和相应跃迁的共振激发,可采用失谐量互补的两束激光同时作用于系统,通过双光子共振吸收过程提高电离几率。

To search for the optimum physical parameters for improving the probability of resonance-enhanced multiphoton ionization（REMPI）,this paper simulates and analyzes the influence of parameters matching of the pump and probe lasers on the double-color double-REMPI probability.The density matrix equation theory that describes the interaction between light and matter is adopted.It is found that the best matching condition for improving ionization probability is：（1）both intensities and pulse widths of two lasers are larger and equal to each other.（2）There is no relative time delay between two lasers and the frequencies of two lasers are resonant with the corresponding transition.As for the ionization process of 1＋1＋1,where one pump and two probe photons are absorbed,the ionization probability is more sensitive to the probe laser.This indicates that in the practical application,if we can not guarantee to realize the optimal matching condition,one should try to improve the intensity,pulse width and frequency of the probe laser.It is also found that if the lasers are not resonant with the corresponding transition,we can adopt two laser beams with complementary frequency detuning to interact with the system at the same time.Thus we can improve the ionization probability through the two-photon resonant absorption process.