The Surprising Behavior of “Whirlpools” of Light

Read the new story by Kendra Redmond on Physics Buzz. I am very happy and at the same time honored that this is about our recent publication on Physical Review X: Spatial Bunching of Same-Index Polarization Singularities in Two-Dimensional Random Vector Waves, by L. De Angelis, F. Alpeggiani and L. Kuipers.

Here a small extract, for the full story click on this link!

It might seem frivolous to study the nanoscale structures of light confined to two dimensions—like something too far removed from daily life to be worthwhile. But consider this: Light is absolutely fundamental to our universe, and understanding its nature means knowing more about our world. The similarities between the behavior of C points and charged particles could point to a deeper insight on the nature of charge and its relationship to light. And, on a related note, the more we know about the behavior of light across different scales and in different conditions, the better equipped we are to harness its power for the advancement of society.

Kendra Redmond

Cheers 🥂

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The peculiar screening of darkness in light

Points of darkness in light are singularities of wave optics, precisely they are singularities of light’s phase, or phase singularities. As light twists around these zeros of intensity, phase singularities are given a topological charge – positive or negative – defined by the direction of this twisting. Interestingly, this topological quantity seems by all means to be an actual charge, since phase singularities “feel” the charge in their surroundings. The way they feel it, is that one singularity of charge plus is always surrounded by a cloud of minuses, and vice-versa, so to try to maintain the total charge in a big box equal to zero. In atomic and molecular physics this process is called charge screening, and in fact we observe this screening to take place for singularities in random light as well.

However, in our recent publication we found something peculiar about this topological screening. To explain it we can play a little game. Let’s take a square box of side L, in which we observe an ensemble of charged entities:

In absence of screening the, total charge in the box would be zero, because every charge can randomly be a plus or a minus. But there will be an uncertainty on the total charge, which intuitiveley scales with total number of charges, i.e., with the area L*L of the box. Naive: the more particles I look at, the more likely it is to have more pluses than minuses.

In presence of perfect screening, the story changes. The total charge in the screen would still be zero, but with a smaller uncertainty! In fact we know that every charge is being compensated by a “cloud” of opposite ones, so to maintain the total charge zero. Nevertheless, this trick will not work at the edges of the screen… So there will still be an uncertainty on the total charge, given by the number of particles near the edges, i.e., proportional to the perimeter L.

Finally, we get to singularities in light. Weirdly enough singularities don’t show neither of the previous behaviours, but they do something in between. In our work we prove that the uncertainty on the topological charge for the singularities in a box of side L scales as ~ L log L, which is bigger than L but still smaller than L^2, proving that singularities do indeed undergo screening, although in a sort of imperfect way.

 

Reference

L. De Angelis, L. Kuipers. Screening and fluctuation of the topological charge in random wave fields, Optics Letters 43, 12: 2740-2743 (2018)

Spintronics & Nanophotonics

Check out the beautiful work of my colleague dr. Su-Hyun Gong on how to couple spin excitations to nanophotonic modes. Electrons spinning clockwise or anticklockwise in a 2D material can here be translated into photons running right or left on a plasmonic nanowire!

And so a direct link is created between the spin information and the propagation direction of the light along the nanowire. It works almost perfectly: the spin information is ‘launched’ in the right direction along the thread in 90% of cases. In this way, fragile spin information can be carefully converted into a light signal and transported over far greater distances.

Feel free to read more information about this on kuiperslab.nl & phys.org, or read the original article on Science!

A Game of Pairs: Spotlight on Light’s Darkness

Nothing lasts forever, and neither does darkness in light. Tangled traces of darkness are left behind by many infinitely small dark points when they move around in random light fields. However, such dark points can be destroyed along their evolution, but always in pairs. New pairs can be  created as well.

evolution_1

In our recent paper, we shine light on the evolution of optical random fields by drawing the attention to the finite lifespan between creation and destruction of their dark points. For the first time, we also take a close look at the lifelong fidelity: the case in which a point of darkness is destroyed with its birth partner. Unexpectedly, we find that the behavior for dark points that remain faithful to their creation partner is distinct from that of “promiscuous” ones. These findings contribute to reveal the complex evolution of the wide class of random systems that the studied case embodies.

Check the original publication on Physical Review Letters and read the news item on PhysicsBuzz!

Emil Wolf Award 2017

I am very happy to share with you the news item that recently appeared on our group’s website! Being selected for, and eventually receiving the Emil Wolf Award has been a huge honor for me. Thanks to anybody who contributed in achieving this.

We congratulate with Lorenzo De Angelis for his recent achievement at the 2017 Frontiers in Optics conference held in Washington DC (USA). On this occasion, Lorenzo was selected as a finalist for the Emil Wolf Award and awarded the final prize for the best presentation in the category “Optical Interactions”. Good job!

check it out at kuiperslab.tudelft.nl

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