PTB, Brilliant photon

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D. Habs, LMU München

• Physics of the vacuum, ultra-high fields and very
  large accelerations
• Larmor- Hawking- and Unruh-radiation
• Planned experiments
• At and beyond the Schwinger limit

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Physics of the vacuum (I)
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Physics of the vacuum (II)
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Schwinger limit and spontaneous pair creation
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Ultra-high fields
focused laser
Schwinger field
coherent harmonic focusing
Lorentz boost e-beam (g 2103)
170 MeV quark-gluon phase transition
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Larmor-, Hawking- and Unruh-radiation
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Larmor Radiation
Radiation polarized in the plane containing
and
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Hawking-radiation from black hole
Gradient field of gravitational forces
Black hole evaporation seen by falling observer
falling observer
Concept of real of virtual particle depends
on reference frame
accelerated observer Atmosphere of real
particles appear to be emitted by hot
membrane surface
falling observer Sees virtual pairs Both parts
of fluctuating wave
K. S. Thorne, Black holes time warps, W. W.
Norton Co, 1994
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Unruh radiation Acceleration radiation (I)
accelerated electron accelerating detector
resting detector in inertial frame second order
process

• Electron ( accelerated detector) absorbs one
  virtual photon
• resting observer sees emission of one real
  photon
• Detector ( electron) re-emits photon
• resting observer sees emission of second real
  photon
• In the inertial frame resting detector
• accelerated scatterer emits 2 real entangled
  photons

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Unruh radiation (II)

• Angular distribution of Unruh radiation
• at 90 to Larmor radiation.
• Entangled photon pairs with opposite spin
• direction with arbitrary direction of one photon.
• TU 1014 K for acceleration a g
• We discuss three cases
• constant acceleration a const.
• first treatment by W. Unruh, unrealistic for
  experiments
• short pulse of acceleration
• small ratio of PUnruh / PLarmor PRL 97 (2006)
  121302
• oscillation acceleration (submitted to PRL)
• monochromatic energy w of Larmor quanta in
  original rest frame of electron.
• wUnruh1 wUnruh2 w , allows for energetic
  separation of Unruh and Larmor quanta.

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Realistic QED perturbation theory with
time-dependent fields

• first realistic theory ? calculation of
  real experiment in QED,
• pair production, Larmor spectra, Unruh
  spectra,
• New range of laser fields at Schwinger field
  strength ES 1018 V/m eES?c mc²
• breakdown of the vacuum in ee pairs
• Electrons are accelerated with 1028 g (106 times
  larger than before)

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Unruh effect for oscillating acceleration (I)
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Unruh effect for oscillating acceleration (II)
E
?

• Suppression of Larmor radiation versus Unruh
  radiation
• energy selection at specific angles
• polarisation measurement

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Experimental set-up

• energy and angular distribution for single
  Larmor photons
• polarisation of Larmor photons
• energy and angular distribution for Unruh
  photons
• proof of correlated pairs of Unruh photons by
  polarisation
• extend field strength to and beyond the
  Schwinger limit

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Hard X-ray Compton polarimeter
3D position, energy, timing, multi-hit
compatibility, polarisation sensitive
36 cm
scattering distribution for 100 polarized
radiation (Klein-Nishina)
Th. Stöhlker et al., A 2D position sensitive
germanium detector for spectroscopy and
polarimetry of high-energetic x-rays, J. Phys.
Conf. Ser. 58 (2007) 411 extended to high
g-energies
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Multiple Scattering in hard-X-ray Compton
polarimeter
simulation for (infinite) Ge crystal
- multiple Compton scattering followed by
complete photo absorption
- information about initial photon polarization
lost after second scattering
- single scattering events - restrict photon
energies to below 200 keV
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Background reduction by kinematic event selection

• - good timing
• coincidence technique
• kinematic event selection
• calculate recoil electron deposition
• precise knowledge of q (i.e. pixel of the
  first interaction)
• ? select only events that obey above
  equation
• scatterer needs to detect these energies
• Eg 200 keV ? Ee 56.3 keV
• 60 keV ? 6.3 keV
  electronic threshold

• - electronic threshold
• dropping Compton efficiency for low energies

low-energy limit for Compton polarimetry ca. 60
keV
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Experimental Set-up at and beyond Schwinger limit
coherent harmonic focus
petawatt- laser beam (1/2)
petawatt- laser beam (1/2)
e (p)
target
B
Compton spectro- meter (GeV)
e- beam (GeV)
capillary (gas-filled)
mirror
e-
e- (p-)
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Beyond the Schwinger limit
? Measure meson production, momentum and flight
time
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Coherent harmonic focusing
Resting mirror S. Gordienko et al., PRL 94
(2005) 103903