Numerical simulation of the resonance photoionization probability by density-matrix equation

An analytical expression of the resonance photoionization (PI) probability is deduced from the time-dependent density-matrix equations that describe the interaction of laser field and material. Based on this expression, the variation of PI probability as a function of some parameters such as laser resonance detuning and Rabi frequency are studied theoretically. It is shown that the increase of the laser resonance detuning will make the PI probability decrease, to some extent, to zero. Both the Rabi frequency and the laser pulse duration will also make the PI probability increase to saturation. It is also found that the variation of PI probability with Rabi frequency is independent of the ionization rate, which will influence the saturation PI probability only. The larger the ionization rate is, the higher the saturation PI probability will be. These theoretical research results provide a useful guide for the practical application of PI spectroscopy.

► PI probability is derived from density-matrix equations for the first time.
► PI probability decreases with the increase of resonance detuning.
► PI probability increases with Rabi frequency until saturation.
► The PI rate doesn't influence the variation of PI probability with Rabi frequency.