  The single Anti-Reflecting (AR) layer is a classical problem in optics. When
all materials are pure dielectrics, the solution is the so-called lambda/4
layer. Here we examine the case of absorbing layers between non absorbing
media. We find a solution for any layer absorption coefficient provided that
the light goes from the higher towards the lower index medium, which
characterizes backside layers. We describe these AR absorbing (ARA) layers
through generalized index and thickness conditions. They are most often
ultrathin, and have important applications for high contrast imaging in fluid
cells.

Optics