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)