Dynamics of optically levitated nanoparticles

This PhD project focused on establishing an optical levitation setup and developing a methodology for dynamically measuring silica nanoparticles' motion. The setup accommodates both spherical and non-spherical particles, employing a tightly focused 1064 nm laser to create an optical trap. Aligned optical elements and a spatial filter ensure a clear Gaussian beam profile, with dynamic motion detected through a differential detection system.

To boost sensitivity to external forces, a vacuum chamber lowers pressure, and cooling techniques, specifically cold damping using electrodes, decrease the particle's center of mass motion to 50 K horizontally. Trapping non-spherical particles involves increasing nanosphere concentration in the nebulizer, resulting in torsional vibration and spinning motion. The particles' shape is analyzed using various techniques, including polarization modulation.

The study explores applications for low-frequency sensing, emphasizing seismic motion and gravitational wave detection. Trapping non-spherical particles offers additional control possibilities, such as inducing bi-stability with circularly polarized light. An electro-optic modulator effectively modulates optical potential and facilitates the study of non-linear dynamics.

Challenges like polarization noise are addressed through a polarizing maintaining fiber, while determining precise non-spherical particle geometry is crucial for experiment design. Techniques for determining particle shape and mass involve response to applied force, cooling process analysis, and light scattering patterns.

In conclusion, this PhD project establishes a foundation for advanced sensing techniques using optical levitation, with potential applications in fundamental physics and low-frequency wave detection. Ongoing exploration of polarization noise detection by non-spherical particles holds promise for future breakthroughs.