Plasma Vorticity and Electromagnetic Angular ...

On the use of novel degrees of freedom in the electromagnetic field to extract more information from radiation Bo Thidé Swedish Institute of Space Physics, IRF, Uppsala, Sweden

Fabrizio Tamburini Department of Astronomy, University of Padova, Italy with contributions from the LOIS OAM/radio topology collaboration

J. Bergman, (Uppsala), R. Karlsson (Graz), T. Carozzi (Glasgow), H. Lundstedt (Lund), W. Löwe, W. Baan (Växjö), N. Ibragimov, R. Khamitova (Karlskrona), H. Then (Oldenburg/Bristol), Ya. N. Istomin (Lebedev Inst, Moscow), J. T. Mendonca (Lisbon), S. Ali (Islamabad), B. Elmegreen, L. Amini and O. Verscheure (IBM Research, NY) Instrumentation Seminar, Alba Nova, Stockholm, 25 February, 2010

Phase singularities (dislocations) are to be expected in radio beams propagating through space

Bo Thidé

Instrumentation Seminar, Alba Nova, 25 February, 2009

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Fundamental question: What are the complete physical characteristics of EM radiation? Start from the beginning: the microscopic Maxwell-Lorentz equations

Symmetric under inhomogeneous Lorentz transformations. The concomitant Lie group is the 10-dimensional Poincaré group P(10). According to Noether’s theorem there therefore exist 10 conserved EM quantities. In fact there exist 23 exact continuous symmetries/conserved quantities (in vacuo), plus an as yet unknown number of approximate, conservation laws [Ibragimov, 2008]. Bo Thidé


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Conserved quantities in EM fields and matter (1) Homogeneity in time => conservation of system energy (Poynting’s theorem):

Homogeneity in space => conservation of system linear momentum (gives, e.g., rise to EM Doppler shift):

Bo Thidé


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Conserved quantities in EM fields an matter (2) Invariance under proper Lorentz transformations => conservation of system centre of energy:

Isotropy in space => conservation of system angular momentum (gives rise to azimuthal Doppler shift):

Foundation of ‘angular momentum radio’ and vorticity probing radio and radar methods. Bo Thidé


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Total radiated EM field angular momentum For beams in free space, the EM field angular momentum can be separated into two parts [Jackson, 1998; Rohrlich, 2007; Thidé, 2010]: where

The first part is the EM spin angular momentum (SAM) Σfield , a.k.a. wave polarisation, and the second part is the EM orbital angular momentum (OAM) Lfield . Both the EM linear momentum pfield, and the EM angular momentum Jfield = Lfield + Σfield are radiated all the way out to the far zone! Bo Thidé


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EM angular momentum is a conserved physical observable. Just like the linear momentum (Poytning vector), it that can carry information over huge distances

Bo Thidé


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Mechanical effects of photon spin angular momentum (1936) and of photon orbital angular momentum (1992)

Beth’s experiment, 1936

Bo Thidé


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Difference between polarisation (SAM) and orbital angular momentum (OAM)

Bo Thidé


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EM beam with circular polarisation (SAM) S but no orbital angular momentum (OAM) L Phase fronts (loci of constant phase) Optics (LG)

Radio

M. J. Padgett, J. Leach et al., U. Glasgow, UK; Royal Society

Bo Thidé


Sjöholm and Palmer, 2007 10

Different OAM states correspond to different topological charges (vortex winding numbers) M. J. Padgett, J. Leach et al., U. Glasgow, UK; Royal Society

l=+3

l=+1

l= -4

Bo Thidé

Spiraling Poynting/OAM vectors carry a lot of information! The Jones matrix goes from 2×2 to 2(j+1)×2(j+1), j=s+l .


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Micromechanical action of laser light carrying SAM and OAM

Particles of sizes 1–3 μm irradiated by SAM/OAM laser beams

Spin angular momentum s = 1 Bo Thidé

Orbital angular momentum l = 8


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The generation of beams carrying OAM proceeds thanks to the insertion in the optical path of a phase modifying device which imprints a certain vorticity on the phase distribution of the incident beam.

Imparting OAM onto a light beam Fork holograms are an example of such devices. If the hologram presents N bifurcations, then at the m-th diffraction order it imposes a OAM value equal to N m ħ (Vaziri et al. 2002).

On-axis

off-axis spectrum of OAM

Spiral Phase Plate

s

l = ∆n λ  s = total thickness Δn = difference of refraction indices.

Fabrizio Tamburini

of

the

plate,


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Single photons can carry both SAM (S) and OAM (L) and can be entangled in both of them!

Bo Thidé


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Single photons can carry both SAM (S) and OAM (L) and can be entangled in …(cont’d)

Bo Thidé


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Observations at 94 GHz of angular momentum induced azimuthal (rotational ) Doppler shift

Bo Thidé


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Very readable paper on POAM in astrophysics

Bo Thidé


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Radio OAM can be observed by phased arrays Optimal results with vector sensing antennas Thidé et al., Phys. Rev. Lett., 99, 087701, 2007

Bo Thidé


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Field vector sensing means total configurability

The ultimate radio coronagraph! Bo Thidé


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Radio beam carrying both SAM and OAM Linear momentum (Poynting) flux and E(t,x) vs. OAM flux Mohammadi et al., IEEE Trans. Ant. Propag., Vol. 58 ,2009

Distribution of linear momentum (Poynting ) flux and E-field vectors Bo Thidé

Distribution of orbital angular momentum flux


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Conventional radio telescopes not sufficient. Can we do better? The array of fourteen 25 m dishes at Westerboork (NL), sees nearby objects emitting 1420.4 MHz (21 cm λ H hyperfine splitting) lines

M31 (Andromeda, Local group) Bo Thidé


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LOIS prototype station under construction in Ronneby To be augmented by two outer, concentric rings, with 16 and 24 radio units, respectively, for a total of 48 units with three dipoles each (funding permitting)

Bo Thidé


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Use three orthogonal electric and magnetic antennas to sample the entire EM field vector

To be first used at EISCAT, 2010 Bo Thidé


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3D vector antenna allows entirely new radio Better SNR, polarisation in real time, DOA,… Click on pictures for animation! Real data from a real, live outdoor vector receiver at Ångström Lab in Uppsala. On line since 2003. Vector coherency gives superior SNR relative to conventional scalar intensity

Bo Thidé

Instantaneous wave polarisation from one single vector antenna


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OAM spectrum probing (spiral imaging) – a new scatter radar diagnostic Recent digital spiral imaging experiments (Ll. Torner et al., Opt. Express, 13, 873–881, 2005; Molina-Terriza et al., J. Eur. Opt. Soc., Rapid Publ., 2, 07014, 2007) have demonstrated that probing with OAM gives a wealth of new information about the object under study.

The stimulus…

Bo Thidé


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Spiral (OAM) spectrum imaging results

…and its response

Bo Thidé


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Nonlinear transfer of OAM radio ↔ plasma Brillouin = ion line Raman = plasma line

Bo Thidé


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Plasmons (Langmuir waves) can carry OAM but not SAM

Bo Thidé


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OAM states of photons can be used in the astronomical instrumentation also with ordinary classical light: To improve the resolving power of a diffractionlimited telescope For coronography, to image extrasolar planets.

Now OAM has to be imposed to the light Not directly quantum stuff for now Fabrizio Tamburini


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Improving the resolving power of a diffraction-limited telescope of an order of magnitude!

The James Webb Space Telescope Super Resolution with OVs in diffraction-limited telescopes and other optical instruments

Fabrizio Tamburini

Credit: ESA (C. Carreau)


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1

Fabrizio Tamburini

OV manipulation for detection at the telescope. Producing Optical Vortices with starlight and the problem of atmospheric seeing


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Upps ala,

Astrophysical source candidates emitting light with OAM Perseus-Taurus Auriga-Orion-IRAS-TPreibisch

The Eskimo Nebula Credit: Andrew Fruchter (STScI) et al., WFPC2, HST, NASA

Fabrizio Tamburini

Uppsala, Celsius Workshop 2010

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OAM makes a new (spiral) frequency Ω available Interesting consequences for radio communications

Bo Thidé


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The OAM topological degree of freedom has revolutionised wireless communications

Bo Thidé


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Hyperentangled SAM and OAM photon states break the linear-optics channel capacity threshold

Bo Thidé


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The conventional Shannon dimensionality of 2 can be exceeded by using OAM degrees of freedom

Bo Thidé


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New ideas – new audiences. SETI?

‘…The investigation of new transmission modes by Thidé and Bergman hints that if we do find a signal from ET, we may wish to reconfigure our radio telescopes to look for encoding of the message via such subtle effects as orbital angular momentum. A simple signal may only be a cipher for a more complex message, and there may be more things in heaven and earth than even Maxwell had dreamt of …’ Bo Thidé


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LOIS has given rise to many articles in the press

Bo Thidé


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Thank you for your attention

....there may be more things in heaven and earth than even Maxwell had dreamt of … Bo Thidé


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Plasma Vorticity and Electromagnetic Angular ...

Plasma Vorticity and Electromagnetic Angular ...

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