Interferometric tunability of the absorption

When an object is illuminated, it will absorb radiation proportionally to its absorption coefficient: Darker portions of the object will absorb more light than more transparent ones. Is there a way around this? In this paper we analyze a setup which uses classical light sources (i.e. coherent beams) and permits to easily tune the quantity of a light absorbed by an object independently on its transparency, by appropriately tuning an interferometer phase. With the same setup, high efficiency measurements of the absorption coefficient can be performed via a feedback mechanism. The only underlying assumption is that the object introduces a negligible dephasing into a probe beam. Since we can employ quasimonochromatic light, this assumption is met in a variety of systems. Moreover, in the case of objects that have a homogeneous phase image, the dephasing can be easily compensated with the interferometer phase. Our proposal draws inspiration from the so called “interaction-free-measurement” setups, where a partially transparent object can be discriminated from a totally transparent one with asymptotically negligible radiation absorption [1, 2, 3, 4, 5]. Even though such proposals were originally based on single-photon light pulses, analogous results have been obtained also with classical light [6, 7]. The layout of the paper follows. We start by describing the proposed interferometric setup. We show how the absorption peak can be tuned and we analyze the irradiation selectivity. We then give the protocol for high efficiency estimation of η. We conclude by analyzing inhomogeneous objects, which incorporate different transmissivities. Since the process does not involve any quantum effects (such as entanglement or squeezing) one could also analyze it in terms of a classical theory of radiation, instead of the quantum formalism we use here for rigor.