Realistic modeling of the detection modes of the microscopes.

Objectives
To model in a realistic way the microscopes developed at the laboratory by taking into account the modes of detection of the latter. In particular, by taking into account the vertical vibration of the probe, which makes it possible to increase the signal/noise ratio by a system of lock-in detection.

Methods
Development of software of simulation based on the Finite Element Method (FEM) taking into account the complex materials and geometries.

Results and prospects
In order to deal with problems specific to the apertuless near-field optical microscopes, we developed models based on Finite Elements (FEM: Finite Element Method, 2D and 3D). FEM approach makes it possible to describe physical problems with complex materials and geometries, harmonic or stationary, i.e. time independent. We already studied, using 2D codes, the influence of certain experimental parameters on the electric field enhancement at the end of the probe. We also showed in 2D, that it was necessary to model the mode of detection of the microscope. In particular, the vertical vibration of the probe makes it possible to increase the signal/noise ratio by using a lock-in detection. We also showed that a realistic modeling of the signal requires to really consider this vibration and thus implies the computation of the signals obtained (i.e. matter-radiation interaction) for the various positions of the probe. Even if FEM codes developed until now enable us to describe a number of problems, we must extend them in 3D in order to be able to compute true orders of magnitude rather than quantitative laws of behavior.