The ability to optically detect the electron paramagnetic resonance (EPR) of a single nitrogen-vacancy (NV) defect in a single diamond crystal has transformed the field of spectroscopy. By attaching a nano-diamond containing a single color defect to the tip of a near-field microscope cantilever, one could build a scanning spectrometer that could locally map the modulation of its EPR response without compromising frequency range, external magnetic field strength, spatial resolution, non-perturbation of the equilibrium texture, sensitivity, or accuracy. However, the general use of such an instrument would require the ability to apply an external magnetic field. This is still an enormous technological challenge, since it requires a solution that allows high-precision control of both the amplitude and the orientation of the external magnetic field. The aim of my thesis was to take up this challenge by focusing on the development of an NV center microscope that fits between the poles of an ultra-stable and orientable electromagnet. This initiative is a collaboration between Spintec and the Institut Néel. This approach introduced significant space constraints on the optical block and the optical interferometer. To this end, I developed a novel type of ultra-compact high performance optical objectives with large numerical aperture, high optical transmission and zero achromaticity. The design is based on a purely achromatic reflective design composed of four axisymmetric surfaces, including two conic elements – a parabola and an ellipse – that share a focal point. This invention is patented. At the same time, an optical bench NV microscopy setup was established to accelerate the development of measurement protocols free from the spatial constraints of using an electromagnet. This setup allows direct evaluation of NV centers and samples by integrating a high performance confocal optical circuit, microwave instrumentation, precision actuators, and timing accurate devices. This apparatus allowed the formulation and implementation of protocols to characterize NV centers in AFM tips, precisely analyzing their properties such as orientations or Rabi frequencies. In addition, it facilitated the first magnetometric assessments on samples using the fluorescence quenching method, validating the system’s ability to generate stray magnetic field maps. The next goals of the project include the refinement of the pulsed sequence protocol to image the spatio-temporal profile of standing spin waves in confined geometries. These methods will first be applied to the optical table NV microscope, with the aim of rapidly extending their functionalities to the microscope operating in the electromagnet.

Plus d'information :https://www.spintec.fr/phd-defense-nuts-and-bolts-approach-to-developing-a-nitrogen-vacancy-microscope-inside-an-electromagnet/
​

Pour suivre la soutenance ​​​en visioconférence : https://cnrs.zoom.us/j/92705963806?pwd=V0xDbkFsUXJiNE0wanI3SEYrK2lxQT09​

​
​​