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CONSTANS Report Summary

Project ID: 340438
Funded under: FP7-IDEAS-ERC
Country: Netherlands

Mid-Term Report Summary - CONSTANS (Control of the Structure of Light at the Nanoscale)

The CONSTANS program aims to explore the ultimate limits of nanoscale light control. The program investigates whether optical entities called optical singularities, which are themselves infinitely small, can be exploited to actively manipulate light at the smallest possible scale and at ultrashort time scales. To this end the singularities will be moved, created or annihilated through all-optical means. The results of this ultrafast control of the nanoscale light structure will be visualized in situ and in real time with a new near-field microscope which is able to distinguish all six components of nanoscale electromagnetic fields in amplitude and phase and for several colours simultaneously.
In the first half of the program optical singularities were investigated in the static situation. Several different nanophotonic structures both dielectric and metallic were evaluated to ascertain their usefulness for manipulating optical singularities. The behavior of the optical singularities was studied in detail. Through experiment, theory and simulations we found that various strategies for creating optical singularities with nanostructures are viable. Moreover, we determined that both photonic crystal waveguides and plasmonic nanowires are promising routes for enhancing the required nonlinear optical interactions.
We have shown that plasmonic nanowires are ideally suited for the fasted nonlinear processes as the optical bandwidth that they can sustain is huge. We also showed that the intrinsic nonlinear response of the nanowires is sufficient to produce new colours with an efficiency that is large enough for the optical signals to be observed by eye. The disadvantage of the plasmonic nanowires is that their optical structure in terms of optical singularities is somewhat limited. Photonic crystal waveguides on the other hand offer a rich arena for manipulating optical singularities. The singularities in the electric field have a behaviour that is distinct from the behavior of the magnetic singularities and this difference can be tuned through a control of the slowdown factor of the light. Through an investigation of soliton fission in slow-light photonic crystal waveguides we ascertained their potential for nonlinear control, albeit over a smaller bandwidth than the plasmonic nanowires. It turns out that arrangements of subwavelength holes in metal films could turn out to be the most versatile platform for manipulating optical singularities. A variety of singularities can be created or annihilated through the adjustment of just a single parameter. The process of creation and annihilation in itself is very intriguing. Another broadband arena for the creation, annihilation and motional control of optical singularities was discovered: chaotic nanophotonic cavities. We have investigated the spatial distribution of singularities in such cavities and showed that the vector nature of the confined light affects how they are arranged in space. Our observation of rogue waves in these cavities demonstrates their potential for ultrafast nonlinear control.
In order to carry out all these measurements great progress has been made in our vector SNOM that is able to map all the six components of electromagnetic waves confined at the nanoscale. Experimentally, our detection scheme has been optimized. However, the greatest breakthrough has come in the interpretation of our field maps. Using the reciprocity theorem we are able to model our experiments without adjustable parameters. Thus, we have gained unprecedented insight into near-field mapping of nanoscale fields, allowing the separate visualization of both the electric and magnetic field.
An unanticipated development in the program was the realization that local optical spin can be used to control the absorption and emission of quantum transitions which involve a change in orbital angular momentum. The potential to explore all the ramifications of this development played an important role in my positive response when I was explored by Delft University of Technology to move my group to the Quantum Nanoscience department of the Kavli Institute of Nanoscience.

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