A five-level quantum system including two low-lying states and three excited states of the ladder type coupled with four laser fields is investigated as it relates to dressed-atom models, and a dressed state is found to be independent of the ionization decaying from the highest level. Under general conditions, half of the initial population of the two low-lying states is trapped in the dressed state, leading to a low probability of ionization. Based on the analytical results, two schemes are proposed for removing population trapping. For a five-level system with hyperfine structures, such as the system for ionizing 235U atoms, population trapping takes place when the laser fields are weak and can be gotten rid of by an increase in laser intensity.
© 2003 Optical Society of America
Xi-Jing Ning, "Removing population trapping in a five-level system with fast decay," J. Opt. Soc. Am. B 20, 2363-2367 (2003)