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TEDxBologna - FabrizioTamburini - La scoperta e la dimostrazione dei vortici ottici della luce (Discovery and demonstration of optical vortices in light)

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(Music) Good morning. Thank you for your attention. It is an honor for me to be here at TEDx and to share some ideas on light and the electromagnetic field. We will talk about electromagnetic vorticity. I was trained as an astronomer, then I obtained a Ph.D. in Theoretical Physics, and I shifted my interests from the sky to particles, relativity and so on. I would like to explain you a different approach to astronomy and its immediate applications to our daily lives. Interestingly, when we receive signals from stars, when we see the stars, we receive all the information, or almost all of it, from the light that arrives here. And the nicest thing an astronomer does, is to analyze in detail the light coming from the stars, since we cannot go there unless it is a not-too-distant planet in our solar system. So what can we do? The light is the main vector of information. So we generally use the intensity, the well-known magnitudes, the wavelength, the color, the spectroscopy to identify the atomic species, the chemical composition of stars, or polarization to show certain properties of the electromagnetic field - light is just a manifestation of the electromagnetic field - and we can see if there is dust or interstellar plasma that can polarize light but we will talk about it later on. There are other properties of light that are still not used. One of these, which I will now describe to you, is the Orbital Angular Momentum (OAM). A rather fancy word for a very well known application here in Ducati. When you ride a motorcycle, the angular momentum of the wheel keeps you upright, the faster you go. When you see riders bending on the track it's thanks to the OAM which keeps them upright. You can bend if you play with your weight and the angular momentum generated by the matter of your wheel. Light also shows these properties. Light is essentially an electromagnetic wave. So we only see a tiny portion of it, that is the visible spectrum, from violet to red, then infrared radio and ultraviolet X and gamma rays. All this derives from an elegant formulation written by Maxwell in 1863 -- if I remember well. Polarization, for instance, is an orientation, a spatial property of the electromagnetic field which allows it to oscillate on a particular plane either clockwise or anticlockwise. We can use it to make 3D films. We use one polarization on a plane for one and another polarization for another plane and we can create a virtual three-dimensional image. There is also another degree of freedom which derives from these properties of lasers. They are called cavity modes. Basically, these lasers have the property to have a longitudinal field and generate spatial traces of light. So, since light can be seen as an oscillation in time of the electrical field, we can control it, in a certain way, using a spatial property of vorticity. You can generate them using special lenses shaped like a spiral staircase. -- in a moment you'll see the ones we made in the radio wave, and you can give them a whirling movement in the space of a wavelength. So, if you think at more dimensions, for instance the dimension of time and space oscillating in time, we get a color, and a torsion in space generating the angular moment. A trace of intensity can be one Gaussian dem, that is a simple dot like this laser pointer, whereas if you have vorticity you can have a circular shape since there is no defined phase inside. So Nature which is very wise does not create a phase singularity but the field turns off in the inside. The nicest thing is that if we place a nanoparticle here - we have done many experiments - this particle starts to turn like a friction only made of light. Many of these experiments found an application in nanotechnology, and biology, like optical tweesers and optical spanners which are used to move elements and samples on the glass of the microscope. Because of this property, light looks like a fusilli-pasta-shaped beam or, as I like to say, photons are drunk that is, in the phase the wave front is coded like a spiral staircase. And these properties of light are coded in natural numbers. So, you have vorticity zero in the natural light one, when you have one twist in the space of a wavelength, two and so on and we have evidence to prove it. To become familiar with the real formalism it is not advisable to use Feynman's approach, that of the quantum mechanics or quantum electrodynamics, since, in the case of a multiphoton beam, paradoxically, it is easier to use Ettore Majorana's formalism which can be found in the notes he left before he died in 1938 and from which I draw much inspiration. Even in the last work with neutrinos - I am changing the subject here - we took Majorana's formalism and we could fit the whole paradox of that supposedly found measure. In this case, Maxwell's equations of the electromagnetic field acquire a special quantum value and you can describe vorticity. We did it in a very interesting work. Applications. As an astronomer, I am interested to see the maximum number of details with the spatial telescope since I can only send a telescope of a certain size into orbit. We demonstrated mathematically, numerically and experimentally that we can increase by an order of magnitude, that is of at least 10 times or even up to 50 times in the event of coherent light, the possibility of any optical instrument to see details. We simulated two close stars and with the vortex we went further what is called Rayleigh's criterion which seemed an almost unbreakable barrier - it is not a physical law, it is a criterion which we can control. So the next patent application deals with microscopes. But I cannot tell you anything about it since it is still being patented. We tried to apply them to astronomy. These are the first vortices we obtained from a double star. We disseminated them in a spectrum in the different frequencies in order to have more information And you can already see the hole in the center indicating a certain vorticity. This is useful to see if we can control the light of the stars. It is very difficult because light is scarse, there are few photons. Then the atmosphere, the collimation with the telescope, and all the rest make it a bit hard. Everything is fine on paper, but when you go in the real world or in the lab or even worse on the telescope, sometimes you only have one try and then you cannot replicate the experiment because there are transient phenomena like supernova explosions and so on. And if you miss that one, you won't get another. That's essentially the concept of being an astronomer. There is an old telescope in Asiago and here we assembled this device and we managed to obtain the first vortices We are interested to see what this information can tell us -- Let's take for example a blue galaxy, a very distant one where there is matter such as clusters of galaxies and so on and we are here on Earth, on the Milky Way. We can either see if there is matter, distributions of plasma which give traces to the light passing through it and we can have information on the distributions of plasma, on the atmosphere and so on. You can imagine the applications of the light orbital angular momentum on everyday life. We can get the information from the phase and we have an idea of what caused the reflection or what passes through it. An example is the gravitational lens. As you know, light can be bent by gravity. The experiment was carried out in 1919 by Sir Arthur Eddington and Einstein. This was the first proof of General Relativity. This is a real image of a blue galaxy and it is all shredded into arches by this cluster of galaxies And so, from the distribution of light of the blue galaxy, we can get an idea of the obscure matter and the visible matter within the galaxies. Thanks to OAM, as we recently demonstrated in Nature Physics, -- it is a theoretical calculation -- we can see the rotation of this lense and the torsion of the gravitational field and finally we can measure the vorticity of a rotating black hole. This is also a test for relativity. There are some practical applications and we made them right away. If we can get information from the stars, we can even use the same principle to transmit information. So if these are indipendent states in the same frequency, we can imagine to build a channel of communication for each one of the states of spatial occupation linked to the orbital angular momentum. They are quantumized states, natural channels within the same frequency. We appeared on Nature later on, with the announcement of the experiment which was first carried out at Uppsala in Sweden - last December 2010 - in the largest anechoic chamber in Europe. We succeded in generating the first radio vortex in WiFi. We expected that result at an experimental level. So we can transmit information via radio and create an artificial channel of radio transmissions using vorticity. And we actually did it. We asked to use Palazzo Ducale in Venice and San Giorgio Island. We did a demonstration experiment at a propagation distance of approximately 500 m. This is San Giorgio Island where we placed the transmitter. Palazzo Ducale was the receiving station. And we could read two channels of demonstration - one without vorticity and the other with vorticity - on the same frequency. As observers, there were a member of the Svenska Akademien and many other external fellow scientists like Sir Michael Berry who first proposed the electromagnetic vorticity in 1975. Also, other scientists came to validate the experiment which will be published on an internationally refereed journal. This is the first device used by Marconi, and this is our device with the vorticities. Here we made a parabolic-shaped phase mask, and we transmitted vorticity. And we proved it! Here it's me and Professor Thidé of Uppsala pointing at the place in the turret where we placed the transmission. Guglielmo Marconi used to anchor its boat Elettra here. Elettra Marconi [his daughter] also came to help us. Here is when we received the signal. There was an amusing media event show and we appeared on the front cover of ScienceNews -- I think it was last July. There are several conclusions to draw from all this. Astronomy, the Accademia, research and so on -- it's not true they are useless. Look at the applications they can have: from relativity to astrophysics and so on. This is a new world for telecommunications. And we have already started with new perspectives, telecommunications, more channels. So we will setup a spin off to start applying all this knowledge to the real world. Thank you. (Applause)

Video Details

Duration: 14 minutes and 59 seconds
Country: Italy
Language: Italian
Producer: TEDxBologna
Director: Andrea Pauri
Views: 101
Posted by: paolalb on Mar 26, 2012

A renowned astrophysicist and a researcher at the University of Padua, also called the new Marconi, Tamburini's findings in optical vorticity will provide a new way to test Einstein's theory of relativity. "We only use 1% of the light frequency possibilities," he explains "but the so-called optical vortices will allow us to have up to 601 transmission channels on the same frequency."

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