Development of metasurfaces for the optical detection of chiral molecules

Context : This PhD thesis topic will focus on the theoretical, numerical, and experimental development of metasurfaces for the optical detection of chiral molecules. To achieve this, we aim to max-imize the chirality of the electromagnetic field at nanoscale volumes close to the metasur-face. Optical detection of enantiomers is motivated by numerous applications, but studies have mostly focused on the development of chiral nanostructures inducing strong circular dichroism. In this thesis topic, we aim to create intense chiral fields with achiral structures.

Theoretical and Numerical Work : From a theoretical standpoint, we will study the conditions that maximize the chirality of nearfields by studying the spectral response in the complex frequency plane. The conditions capable of maximizing both electric and magnetic near fields are not yet fully understood, and we will seek to establish the solid theoretical foundations leading to these conditions in metasurfaces, particularly through the complex analysis of metasurface reflection and transmission coefficients, as well as through algorithmic optimization approaches. A second major aspect of this thesis work will involve modeling a chiral medium. This work requires working with complete constitutive relations and their implementation into numerical models for solving Maxwell’s equations. Subsequently, a layer of chiral material will be integrated into the immediate vicinity of the metasurface to evaluate the influence of the metasurface on circular dichroism. Once all these theoretical and numerical elements are
achieved and mastered, we can develop and use optimization algorithms to determine the optimal parameters of the metasurface.

Experimental Developments : We will collaborate with the Planète technological platform hosted by CINAM to fabricate samples. The PhD student will follow a 15-day training in the cleanroom (training certified by the doctoral school), and thereafter, the PhD student can continue technological developments to fabricate the samples. The metasurface will be optically characterized at the Fresnel Institute and/or at the INSP and LRS, two laboratories located on the Jussieu campus in Paris Centre involved in the joint project. These works will be carried out within the framework of a project funded by the National Research Agency entitled NanoSpeCD.

Directeur de thèse : Nicolas Bonod, Guillaume Demesy, Brian Stout