INVITED TALK -> Chiral optical Local Density of States in a spiral plasmonic cavity

Chiral metallic nanostructures generate great interests in the study and manipulation of light-matter interactions at the nano-scale. In particular, spiral plasmonic systems have received considerable attention owing to their... [ view full abstract ]

Chiral metallic nanostructures generate great interests in the study and manipulation of light-matter interactions at the nano-scale. In particular, spiral plasmonic systems have received considerable attention owing to their potential for controlling emission properties as well as for their capability to generate surface plasmons (SPs) vortices with tailored orbital angular momentum. They are expected to open new possibilities in applications ranging from biochemistry to quantum information processing. Therefore, a full characterization of system's photonic properties, provided by the optical local density of states (LDOS), is thus required. In this work, we report the observation of chiral optical LDOS in a spiral plasmonic nanostructure, in both classical and quantum regime. We demonstrate using scanning near-field optical microscopy (NSOM) in combination with spin analysis that a spiral cavity possesses spin-dependent local optical modes and features optical spin Hall effects as well as orbital angular momentum selection rule. To achieve this investigation in the classical and quantum regimen both aperture NSOM tip and quantum source based probe are considered. The later consists of a few nitrogen vacancy centers hosted in a diamond nanocrystral that is grafted at the apex of the near field probe following a method developed in our group. The orientation of the SPs dipoles induced by these probes will be discussed and characterized by leakage radiation microscopy. In addition, our theoretical model analytically describes the photonic partial LDOS maps in terms of Bessel functions whose order can be directly related to the spin and the geometrical charge of the spiral. We expect our method to bring an important contribution in future characterization and design optimization of plasmonic chiral systems.