Lasing in a two-level atomic system without population inversion

Baqer Obaid Al-Nashy, Muwaffaq Abdullah, Ali Gehad Al‐Shatravi +1 more

Yifu Zhu

It is shown that a closed V-type, three-level system, which is incoherently pumped on the transition at which lasing occurs and coherently pumped on the other transition, exhibits lasing without population inversion in any atomic state basis. The same system can be also made to exhibit lasing without population inversion in the bare atomic state basis but with population inversion in the dressed-state basis.

Krishna Rai Dastidar, Lipika Adhya, Ratan Kumar Das

Paul Mandel

When an atomic system interacts with light, it can amplify the electromagnetic radiation when gain exceeds loss. This requires that transitions from the upper level to the lower level prevail over the transitions from the lower level to the upper level. If one deals with a two-level system, the only way to obtain amplification is to create a state of population inversion, i.e. the upper level must be more densely populated that the lower level. "Lasing without inversion" may be possible when part of the atoms are trapped, which removes them from the subspace of states with which the upper level can have transitions. This chapter determines to what extent population inversion is necessary to achieve amplification. Independently, amplification without inversion and lasing without inversion were predicted by Harris using a different type of atomic interference. The amplification threshold has a number of features that are reminiscent of the laser threshold.

Shangqing Gong, Si-de Du, Zhizhan Xu

Shi-Yao Zhu, Marlan O. Scully, Ernst E. Fill