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Creating motion faster than light.

What happens when light falls on something moving faster than light? The question might seem meaningless - after all, according to relativity, nothing can move faster than light.

But even though no object can move faster than light, it is possible to create "synthetic" motion that is faster! The trick is to change the properties of a material in a way resembling a Mexican wave in a stadium: Although no one leaves their seat, their organised motion creates a wave. In the same way, a "wave" of changing properties of a material travels faster than light.

In our just-published Nature Communications paper, we do this experimentally. By shining intense laser light on a material called Indium Tin Oxide, we create a wave of changing properties that travels faster than light. When light falls on this moving motion, it creates new colours (frequencies) of light that are scattered in different directions. This space-time diffraction is similar to the phenomenon of Doppler effect, where the sound of a passing train reaches us at a higher frequency when it is moving towards us and at a lower frequency when it is moving away from us. We show that the experimental results of Doppler effect match the prediction from Einstein's theory of relativity of a particle moving faster than light exactly, once we extend it to work with speeds faster than light by letting time and space be imaginary!

Read the paper here: https://www.nature.com/articles/s41467-025-60159-9/

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Increasing the power of lasers is tricky because new, unwanted forms of light ("modes") appear when we increase the light intensity. One way around this is to combine multiple lasers together, so that each one has a lower intensity. But even this method ends up resulting in one mode that we want, along with other unwanted ones that can reduce the quality of the laser light for some applications.

We show theoretically that, by making the multiple lasers interact with each other with a delay, we can create an unusual "exceptional point". By making the lasers work beyond the exceptional point, we can remove all these unwanted modes.

Read the full paper here: https://pubs.acs.org/doi/10.1021/acsphotonics.4c01230

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Gold is shiny because of electrons that oscillate when light falls on it. Tiny gold #nanoparticles make these oscillations respond strongly to certain colours. Thousands of these particles arranged in a large array react together to a very narrow colour range.

We place this array on a semiconductor to create a novel #laser. These lasers could one day be placed directly on semiconductor chips, promising applications from optical communication to LIDARs.

https://pubs.acs.org/doi/10.1021/acsphotonics.4c01236

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Daily materials absorb colours of light differently but cannot change colours directly. Their properties are also fixed in time.

Shining powerful lasers on some materials can overcome both limitations: It can create light of double the frequency, and change the properties rapidly.

We study the modification of the frequency-doubled light when material properties change rapidly with time. We show that this effect can be used to do some computations!

https://www.nature.com/articles/s41467-024-51588-z

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Modern #lasers come in various shapes and sizes, far from the high-school picture of a gain medium between two mirrors. We fabricate a spider web-shaped semiconductor laser, smaller than the width of a human hair. It can output light at different colours, and is very sensitive to pumping parts of the network. Such lasers are promising for integration in photonic chips. We are currently teaching such lasers to do #ImageRecognition !

Read the paper here: https://onlinelibrary.wiley.com/doi/10.1002/lpor.202400623

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We fabricate two #semiconductor #nanolasers placed extremely close together (separated by a thousandth of the width a human hair!) to couple their electromagnetic fields. By using a cool experimental technique to apply different gains to the two nanolasers, we demonstrate experimentally and theoretically a lot of interesting phenomena that we believe will have applications in diverse fields from optical computing to data transmission.

Read it here: https://www.nature.com/articles/s44310-024-00006-9

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#Nanoparticles can focus light way stronger than any lens, and allow us to make light and matter interact in unusual ways. But what is the best shape for a #nanoantenna to enhance light emission from molecules? A cool simulation method called topological optimisation has previously shown that a certain "infinity antenna" shape is best for this enhancement. Here, we fabricate these antennas and show how strongly they enhance light emission.

https://pubs.acs.org/doi/10.1021/acs.nanolett.3c03773

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#Chiral (left/right-handed) molecules are crucial to biochemistry. Light can distinguish between them but interacts too weakly, and boosting with #nanophotonics is not easy because it destroys chirality of EM fields. Typical solution is to design #nanostructures with highly chiral field that makes molecules absorb circularly polarised light differently. Here we find a much stronger effect where the molecules make nanostructures absorb light differently!

https://pubs.acs.org/doi/10.1021/acs.nanolett.3c00739

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#Chirality of #BioMolecules (left/right-handedness) is central to life. Light can be chiral too, a tool to interact with them. Light can also excite spins in #2dSemiconductors and rotate objects. #Nanophotonics can enhance these very weak effects. We surprisingly found that different phenomena, all relying on chirality of light, are incompatible! And found design rules for #metasurfaces for enhancing different chiral interactions (led by @albertogcurto).

https://doi.org/10.1021/acsphotonics.9b01200

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Scientists use #nanophotonics to improve light emission. The strong electric field near nanostructures can excite molecules and extract light from them more efficiently, creating better light sources. We usually model this by assuming that the emitter stays fixed. But in many practical materials, emitting #excitons move around! We found a recipe for making such devices better by figuring out how to do calculations more correctly (led by @albertogcurto): https://onlinelibrary.wiley.com/doi/10.1002/adom.202200103