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J.T. Mendonça

Photon acceleration as a scattering process. J.T. Mendonça. Instituto Superior Técnico, Lisboa. Outline. Historical background; Photon acceleration models; Acceleration in a laser wakefields; Ionization fronts and particle beams; Scattering by relativistic plasma bubbles;

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J.T. Mendonça

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  1. Photon acceleration as a scattering process J.T. Mendonça Instituto Superior Técnico, Lisboa

  2. Outline • Historical background; • Photon acceleration models; • Acceleration in a laser wakefields; • Ionization fronts and particle beams; • Scattering by relativistic plasma bubbles; • Photon acceleration in gravitational fields; • Generalized Sachs-Wolfe effect; • Conclusions.

  3. Historical background • Relativistic mirror (Einstein, 1905) • Moving ionization fronts:(Semenova, 1967; Lampe et al., 1978). • Moving nonlinear perturbation: adiabatic frequency shift (Mendonça, 1979). • Photon acceleration in a laser wakefield (Wilks et al., 1989). • Time refraction (Mendonça, 2000).

  4. Experimental evidence • - Laser self blue shift: flash ionization (Yablonovich, 1974, Wood et al., 1993). • Microwave experiments: ionization fronts (Savage et al., 1992). • 2D optical experiments (Dias et al., 1997). • Photon trapping in a wakefield (Murphy et al., 2006). Related optical phenomena: self and cross-phase modulation, super-continuum (70’s); Unruh radiation!! (2010)

  5. Theoretical models • - Classical model: • Geometric optics of space and time varying media • - Kinetic model • Photon kinetic theory (laser as a photon gas, photon Landau damping); • - Quantum model • Full wave theory (similar to scattering theory in Quantum Mechanics); • - Second-Quantization model • Quantum optics approach (theory of time refraction and temporal beam splitters); • Extension to other types of interaction • neutrino-plasma physics, gravitational waves.

  6. Refraction Time refraction y ct q  2 2 n n 2 2 x x n n 1 1 q  1 1 W = Inv Photons cannot travel back in the past

  7. Space-time refraction (moving boundary) c t a 2 x n 2 n a 1 1 Generalized Snell’s law Invariant

  8. Photon ray equations • Photons  relativistic particles with effective mass • Photon Dynamics  canonical equations of motion Hamiltonian Force acting on the photon: refraction (inhomogeneous plasma) and photon acceleration (non-stationary plasma).

  9. i,ki i,ki v=c v=c f,kf f,kf f,kf v=c v=c Photon interraction wit ionization fronts Counter-propagation (+) Co-propagation (-) gas gas plasma plasma • Reflection in counter-propagation (relativistic mirror) • Plasma formation (flash ionization) 

  10. Intense laser pulse in a gas jet Relativistic ionization fronts Shadow images of a relativistic front t0 t1 (Experiments done in collaboration with LOA, France)

  11. Photon acceleration Laser pulse 65 fs, 2.5 mJ @ 620 nm Counter-Propagation Co-Propagation Simultaneous measurement: b=0.942, n=4.26 x 1019 cm-3 Dias et al. PRL (1997)

  12. Photon dynamics in a wake field Phase space plot Laser probe diagnostic for laser accelerators Wakefield = relativistic electron plasma wave produced by a pump laser pulse frequency shift

  13. Photon trapping in laser wakefield R. Trines (simulations) C. Murphy (experiments)

  14. Confirmed by PIC code simulations

  15. Laser wake field experiments at RAL C. Murphy et al. PoP (2006)

  16. Photon scattering by a ionization front Beta 0.997 nAr 1x1019 cm-3

  17. Photon Scattering by a relativistic plasma bubble x  z X=s/i Scattered frequency =0.99 0.95

  18. Photon-bubble scattering problem (ks,s) (k0,0) v

  19. Photon acceleration in a gravitational field scenario Cosmic Temperature map WMAP_2008

  20. Sachs-Wolfe effect is photon acceleration Low plasma density limit Low frequency shift limit Mendonça, Bingham and Wang, CQG (2008)

  21. Moving perturbations Dynamical invariant Generalized Sachs-Wolfe Purely vacuum perturbations This is not a Doppler correction!

  22. Photons in a Gravitational wave Perturbed flat space time Weak gravitational wave Photon dispersion relation

  23. Nearly parallel photon propagation Perpendicular photon motion y x Parallel photon motion

  24. Photon acceleration by gravitational waves Gravitational wave frequency: W=104 s-1 and amplitude A =10-4 Typical photon trajectories t=Act/2

  25. Conclusions • Photon acceleration is a first order effect; • Experimental evidence: relativistic fronts, wakefields (plasmas), self and cross phase modulations (optics); • It can be seen as space-time refraction; • It can also be seen as a scattering process; • Interaction with Gfields and Gwaves ( ray bursts, Sachs-Wolfe effect); • Applications: plasma diagnostics, ultra-short laser pulses, sub-cycle and attosecond optics, tunable radiation sources.

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