Control of radiative properties by introducing a periodic microstructure into the material

Thermal emission is typically incoherent, unlike laser emission. However it could be interesting to control this emission to create a highly directional and monochromatic thermal source for purposes in photovoltaic (for example). We are only interested in special type of materials: we study materials, which support surface waves (surface-phonon polaritons for polar materials and surface-plasmon polaritons for metals). These surface waves are particular in the way that they exist only in the near field. By ruling a grating on the interface, we create a resonating excitation of these surface waves, which allows an emission in the far-field.

Those gratings — periodic microstructures introduced into  the material — are the main focus of our study.



1D and 2D gratings
1D and 2D gratings

The objective is to control the radiative properties of these structures in order to design objects with particular thermal properties, such as structures that can emit on a very narrow band of wavelength and be very reflective at other wavelengths.

The study is mainly numerical; we use the RCWA (Rigorous Coupled Wave Analysis) method to calculate the emissivity of those type of structures.

There is no linear approach to solve the problem. So, we tried many different ways, dissociating:

-the possible configurations

-the influence of the parameters

-interesting materials

Finding the best material combinations and the best configurations for the grating will be the main objective of the thesis.

We could then fabricate the best structures with a FIB (Focused Ion Beam), which should be acquired by the LABEX. By testing the created samples, we could validate the numerical model.