• chiality
• coherent absorption
• coherent perfect absorption
• metamaterials
• scattering matrix
• singular values
• singular vectors
• symmetries

An object is defined as chiral when it cannot be superposed with its mirror image via proper rotation or translation operations. Chiral media exhibit both circular birefringence and circular dichroism, that’s to say left and right circularly polarized light propagates in chiral media with different speeds and different losses. Enhanced chiroptical response, can be obtained by working with metamaterials. In a metamaterial, the particles of a certain “base” material are arranged, usually in a periodic manner, in such a way that their effective, collective properties meet specific targets in terms of near-field structuration and/or far-field scattering profile. Metamaterials can be constituted of lossless materials, thus implementing unitary scattering operation, or may contain loss/gain elements, resulting in non-unitary behavior. An extreme case of non-unitary metamaterials is that of coherent perfect absorbers (CPA), i.e., objects that dissipate internally all the electromagnetic energy supplied from the far-field, provided that specific phase, amplitude and polarization conditions on the incident field are met.
Recently it has become of great interest combining chiral response with perfect absorption. Since 2016, some research groups tried to retrieve this phenomenon in chiral materials.
Within this research context is located my master thesis project, that aims at producing experimental evidence of a polarization dependent coherent absorber operating in the visible wavelength range. In the first part of the thesis, using the Rigorous Coupled Wave Analysis, we calculated the scattering matrix of a metal-dielectric-metal patterned metasurface, with a pattern of L-shaped air holes, optimized to work as a chiral metasurface absorber (CMA) in the visible spectral range. In the second part of the thesis two different samples of the metasurface were tested using an interferometric setup with a Helium-Neon laser as coherent input source, whose polarization state was appropriately set via four polarizers. This setup allowed us to study the absorption of the surface as a function of the polarization of the impinging light, which was the main strength and original contribute of our work, because the other works mainly use circularly polarized light of a single handedness showing that it produces CPA.