Optical force spectroscopy in microfluidic devices

Nanodiamonds embedded with an ensemble of fluorescent defects such as Nitrogen Vacancies or Silicon Vacancies are an exciting quantum material. Their size, brightness and spin-coherence properties make them particularly attractive for nanoscale bio-imaging that includes thermal and magnetic sensing. An outstanding issue for nanodiamonds is the non-uniformity in size and brightness. This non-uniformity could be addressed by better protocols for synthesising homogenised nanodiamond or through sorting based on size and brightness criteria, that enable the collection of the most uniform material.

The thesis reports on the development of two different experimental setups, one devoted to the study of resonant optical scattering forces, the other one to the study of optical gradient forces of trapped nanodiamonds. The main focus of these experiments is the optomechanical study of fluorescent nanodiamonds in optofluidic channels. The first part of this thesis details the engineering of an optofluidic setup that serves as the base for developing an open-loop sorting technique. This mechanism uses the colour-centre dependent interaction between resonant light and optical transitions to separate nanodiamonds based on their defect concentration and specific quantum properties. The second part of this thesis focuses on the fabrication of an optofluidic device for the stable trapping of an isolated nanodiamond in an optical trap. The optical trapping setup was used to characterise near resonant trapping of ultra-bright nanodiamonds.

The tools and setup detailed in this thesis provide a solid foundation for the optical forces spectroscopy of fluorescent nanodiamonds and other quantum materials.