Periodic Reporting for period 4 - PSINFONI (Particle-Surface Interactions in Near Field Optics: Spin-orbit Effects of Light and Optical/Casimir Forces)
Reporting period: 2021-09-01 to 2022-08-31
Near-field directionality of light, being researched in the PSINFONI project, can provide a fundamental solution to the ultrafast routing challenge described above. In essence, the polarization of light or polarization of a light source may affect light's propagation direction. Hence, all-optical ultrafast switching on light polarization can be used for light switching and routing, without relying on electronics. The inverse scenario suggests the possibility of integrated nano-photonic light polarimeters based on this robust electromagnetic phenomenon. PSINFONI will theoretically and experimentally explore the basic science and potential for devices using these phenomena.
Nanophotonics has also been an enabling technology for advancements in other sciences via the possibility of optical tweezers and optical forces, which received the 2018 Nobel prize in Physics. Researchers in the biological and healthcare sciences, among others, greatly benefit from the possibility of utilizing optical forces to trap, move and manipulate small molecules or even living cells. However, these tools require complex setups to achieve the focusing of a laser beam into very tight volumes to create the optical trap, and subsequent movement of that focus. This allows for movement of one single optical trap at a time, but a massively-parallel movement of several molecules, particles or cells is not easily scalable. The PSINFONI project aims to explore the possibility of achieving optical forces for the manipulation and movement of particles without using focused illumination, instead relying on the particle-surface interactions that occur in the near field when particles close to a surface are illuminated using a simple plane wave, which can then be controlled via the illuminating light polarization. The use of plane waves for optical forces would allow massively-parallel control, movement and/or sorting of vast numbers of particles simultaneously. We also explore the regime of Casimir forces, when no illumination is involved.
Both the near-field directionality of light, and the repulsive and lateral optical forces on particles under plane wave illumination, rely on the near field interactions of polarized particles with a nearby surface or waveguide. The PSINFONI project relies on our expert in-depth knowledge of these near-field particle-surface interactions, allowing us to efficiently explore the space of achievable possibilities in the ideas described above.
This work also inspired us into novel applications. A suitably engineered particle can be placed in a region of optical evanescent waves, extremely easy to do in practice via total internal reflection on a nearby surface, such that we can exploit the electric and magnetic fields to achieve an extremely sensitive position sensor. Tiny subwavelength changes in the position of the particle result in dramatic changes to the directionality of the particle in the far-field. Hence, we proposed how a far-field measurement can be used to detect sub-nanometer displacements of the particle.
In the area of exploiting near-field directionality to achieve integrated nanopolarimeters, we have successfully designed, fabricated, and measured, what is to our knowledge the first subwavelength integrated Stokes nanopolarimeter in a silicon photonic circuit, compatible with CMOS mass-manufacturing facilities. It can be placed in the way of the beam with negligible disturbance. It is therefore a non-invasive, integrated, nanopolarimeter. The fabrication and measurement was performed in collaborations with a group at Universitat Politecnica de Valencia.
In the area of novel optical forces of particles near surfaces, we theoretically showed the first instance of a lateral Casimir force acting on particles near a smooth surface, when the particles are experiencing a rotation. This surprising and counterintuitive physics, which we formally describe as being identical to the mechanism of a wheel but with no contact or friction, ultimately stems from the near-field directionality of circularly polarized dipoles. This work received significant media attention and was picked up by several internet blogs and news websites.
We hav also done considerable theoretical efforts on both lateral and repulsive ptical forces on engineered particles near engineeres surfaces, including repulsive forces near graphene, lateral forces above magneto-optical surfaces, and repulsive forces on magnetic particles near conventional metallic surfaces.