Milano 18. January 2007

Transcription

1 Birefringence in Theoretisch-Physikalisches Institut, FSU Jena with T. Heinzl (University Plymouth) B. Liesfeld, K. Amthor, H. Schwörer (FS-University Jena) R. Sauerbrey FZ Dresden-Rossendorf Optics Communications (2006) work in progress Milano 18. January 2007

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3 QED - basic vertex Birefringence in pair production (absorptiv) photon-photon scattering (dispersiv) γ e γ γ γ e + e. γ γ

4 External Field (e.g. laser) Schwinger effect E e e + exponentially small for E < E c Sauter, Schwinger scale: critical electric field: ee c λ = m e c 2 E c = m2 ec 3 e V m, B c = G I c W cm 2 vacuum polarization: γ + E γ quantum induced NLED (Euler, Heisenberg, Weisskopf,...) birefringence of vacuum Klein, Nigan, Breitenlohner, Brezin.s Bialynicka-Birula 2

5 multi-photon Breit-Wheeler PP (Burke et.al, SLAC 97) nγ L γ e e + NL-Compton: e + nγ L e + γ multi-photon Breit-Wheeler γ + nγ L e + e nγ L from Terawatt laser n = O(10) E e = 46.6 GeV E γl = 2.35 ev (527 nm) E γ = 29 GeV (vs. 111 GeV) O(100) rate of e + production agreement with QED (trident e e + e?)

6 Keldisch adiabaticity parameter of Laser background (BG) regimes: η = E/E c ω L /m e e m e ω L c E rms η 1: low intensity high BG frequency ω L - low-order perturbation theory - standard QED regime η 1: high intensity low BG frequency ω L - multi-photon (high-order) processes important - new QED regime - realised by high-power optical lasers! SLAC-experiment: η = 0.36

7 Laser performance (cf. Ringwald 2003) characteristic Vulkan XFEL XFEL ELI Polaris ( goal ) ω L focus I E/E c η ω L in ev, focus in nm, I in W/cm 2

8 central object: vacuum polarisation tensor Π µν [A] = + describes modified light propagation and PP (via Im) for special BGs exact one-loop results available low-energy limit (ω, Ω 0) = Heisenberg-Euler ω Ω Birefringence in ν = ω/m e, ǫ = E/E c small e.g. X-probe ( 5 KeV), uh-power laser (10 26 W/cm 2 ): ν ǫ 10 2

9 ν standard QED (ǫ = 0) SLAC exp. strong-field QED Birefringence in 1 Heisenberg-Euler regime 1 presently attainable (all optical) ǫ

10 encoded in effective action (fermionic integration) L EH = 1 ) 4 F µν F µν + L (F µν F µν,f µν F µν L : derivatives and powers of, ν 1 constant fields L known (Euler, Heisenberg, Weisskopf,...) ǫ 1 only leading terms in power series expansion L = 2α2 ( ( 2 45me 4 2 ) 2 + b( ) 2) +... QED: b = 7 and Born-Infeld b = 1

11 quantum Maxwell equation for a light probe f µν : strong brackground + probe field F µν F µν + f µν, f µν F µν linearize with F µν quasi-constant α 2 0 = µ f µν 8 45 m 4F αβf µν µ f αβ F αβ F µν µ f αβ Toll 54 Baier, Breitenlohner 67 Narozhniy 69 Bialynicka-Birula 70 Adler 71

12 effective ǫ(, ),µ(, ) observable? methods from nonlinear optics: probe plane wave k = (ω,ωò) f (Ò,, ) = 0 similar to uniaxial crystal: n ± = η ± 2 n ± = Ò ± = 1 + n ± α 45π 2 E 2 c ( Ë ( ) 2 ( ) 2) Ë: Poynting, QED: η + = 7,η = 4, BI: η + = η quantum vacuum induces birefringence detection schemes: PVLAS, BMV, Photon-collider,...

13 phase velocities depend on polarisation α 2 V m 4 2 sin 2 θ B V 1 8 α 2 45 m 4 2 sin 2 θ B Birefringence in linear polarisation elliptic polarisation ψ l = π L v sin2θ, λ v(5.5t) 10 22

14 above threshold (QED: ω > 2m e ) Birefringence in damping κ, = 1 ω Im Π, dichroism induces rotation: θ 1 4 κlsin2θ

15 Polarizzazione del Vuoto con LASer (PVLAS) magnet 6T, 4.2K, 1m rotation of magnet 0.3Hz laser: 100 mv, λ = 1064nm (532nm) cavity finesse: N 10 5, L 60km observed ellipticity signal Birefringence in ψ exp ψ QED 10 4 (preliminary) instrumental artifact? investigated at length without success! new physics? (pseudo)-scalar coupling φf µν F µν or φ F µν F µν? millicharged particles? see Ahlers, Gies, Jaeckel, Ringwald 2006

16 experimental setup (Polaris) laser pulse 50/50 Beamsplitter Birefringence in X-ray laserpulse off-axis parabolic mirror off-axis parabolic mirror polarizer k = ω(1,nˆ ) analyzer birefringence maximal for counter-propagating probe beam n ± = 1 + α { } 14 I 45π 8 I c

17 relative phase shift: focus length d, probe λ: φ = 2πd λ (n + n ) = 4α d I 15 λ I c Gaussian beam: d κz 0 z 0 Rayleigh length, κ intensity integral, : Polaris λ 45 0 d linear elliptical small λ, high I

18 Polaris: ω m e c 2, (backscattered Thomson photons) I I c parameters (ω in KeV, λ in nm, z 0 in µm) ω λ z 0 φ(rad) ellipticity δ 2 Jena XFEL In principle δ 2 = ( 1 2 φ) (E. Alp et.al, Hyperfine Interactions 125 (2000) 45) ELI: δ !!!

19 Birefringence in nonlinear pure-γ effects: Im LEH : Schwinger pair production, vacuum dichroism Re LEH : vacuum birefringence with static -field new physics (Zavattini et al. 2005) light-by-light scattering (Bingham et al. 2005) photon splitting (Adler 1970) include charges nonlinear Thomson scattering (SLAC, JETI) laser induced particle acceleration dressed (Volkov) particles (Matsukado et a. 2000) challenging but feasable! Complementary to particle collider physics