用两束脉冲激光,一束使原子共振激发,另一束使激发态原子电离,当电离光脉冲能量约达1J/cm~2时,可使电离饱和.测量被电离原子数的相对大小与电离光脉冲能量之间的函数关系,可以方便地得出原子激发态的光电离截面.延迟电离光至激发光脉冲结束后到达作用区,可以修正激发光对电离的贡献,并避免电离光引起的Stark位移对共振激发的影响.应用共振激发延迟电离方法测定了Cs原子7~2P(3/2)态的光(λ=5320(?))电离截面,测量值σI=6.5×10~(-18)cm~2与Manson的计算值非常接近.

Atoms are first excited and then ionized by two different laser pulgeg, respectively. When the energy per pulse of the ionizing laser is near 1J/cm2, the ionization is saturated. By measuring the relative number of ionized atoms versus the ionizing laser energy, we can easily obtain the photoionization cross section for the excited state of the atoms. The ionizing laser pulse is delayed until the exciting laser pulse is stopped. It aims to eliminate the contribution of the ionization signal produced by the exciting laser and to avoid the Stark shift produced by the ionizing lager. The pliotoionization cross section for Cs (72P3/2) at 532.0 nm has also been measured. The measured value is σI=6.5×10-18 cm3, which is close to Manson's calculation.