The control and use of light polarization in optical sciences and engineering is widespread. For instance, polarization-resolved nonlinear microscopy allows one to retrieve molecular-level structural information from ordered biological specimens (collagen, cytoskeleton fibers, myelin etc.). Currently, molecular imaging in strongly scattering media is not possible, because of multiple scattering : it destroys the focus necessary for high-resolution imaging, and also depolarizes light, necessary for polarization-resolved approaches. While recovering a focus has been recently demonstrated by wavefront shaping techniques, recovering the polarization state was considered impossible.
In a recent publication from Science Advances, Hilton Barbosa de Aguiar (JRC in department), Sylvain Gigan (LKB) and Sophie Brasselet (from Fresnel Institute) have shown a new effect that recovers a pure polarization state deep inside a complex medium, out of an enormous amount of possible polarization states, and without using any specific state selection as previously used. This was made possible by using the concept of broadband wavefront shaping : the short coherence length of broadband sources allows one to select (set in-phase) only states that have the same polarization as the input.
The authors then demonstrate the implications of such achievement by performing molecular-level structural imaging of biological tissues through scattering media, specimens that are used for diagnosis in biomedical optics (see Figure).
The observation of this new phenomenon is not restricted to imaging, but may open up new exciting opportunities in any field that exploits polarization states, from optical multiplexing in fibers to quantum states in disordered media.