Light propagation in the presence of multiple stellar gravitational lenses

We discuss the light propagation in the presence of multiple gravitational lenses. For that we assume that lenses are separated by large distances from each other and thus are non-interacting. Furthermore, we consider a rather exotic case when the source, the lenses, and the observer are positioned on the same line. It turned out that in this axially-symmetric case, the diffraction integrals are exactly solvable providing us with valuable analytical insights. We observe that the number of Einstein rings formed around each subsequent lens doubles. The overall light amplification depends on the masses of the lenses and is driven by the distance between them. We demonstrate that for practical observing scenarios, the two lens system does not provide for an additional light amplification compared to the case with a single lens transmission. However, the use of the second lens may bring some technical advantages including significant beam compression, improved beam quality, increased signal power density, and potential use of smaller size telescopes at the receiver.