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3. 2 nd International Conference and Exhibition on Lasers, Optics & Photonics 09/08 /2014 2 nd International Conference and Exhibition on Lasers, Optics & Photonics 09/08 /2014 Polarization evolution; a method to measure nonlinear interaction in light filaments Ladan Arissian

4. 1)Laser filamentation in air ; a balance between electronic Kerr focusing and plasma defocusing 2)Nonlinaer polarization; a spatio-temporal effect 3)Tunnel ionization follows the light polarization (also the electron current ) Outline

5. Self- focusing ionization e-e- Self- focusing ionization e-e- Filament is a unique light-matter interaction in which both light and matter have to be fully considered. Laser filamentation in air

6. Filamentation theories Moving focus Self-induced waveguide: balance between Kerr lensing and plasma defocusing Beam reshaping Axicon focusing Bessel beam surrounding “reservoir” n(I) changes sign at filament intensities

7. Electron Molecular and Electronic Kerr Radiation from filament THz Multi color and Nonlinear process Pre excited medium 1.Pre-filamentation propagation 2.Polarization evolution 3.Fluorescence 4.Nonlinear interaction Stimulated Backward Raman Four wave mixing 5.Electron current 6.THz detection

8. Measuring polarization state Polarization effect on phase modulation and macroscopic properties of filament a b E ox E oy x y  Ellipticity=a/b Angle of the QWP Ellipticity t cube = Final state of polarization Angle of the QWP Orientation of the ellipse

9. Non resonant electronic Kerr Molecular Kerr Sources of polarization modification

10. Electronic Kerr Peak power 10TW/cm 2 Molecular and electronic Kerr

11. Vacuum chamber QWP Grazing plate Rotating polarizer cube x Angle of the ellipse at focus prior to the filamentation Focusing in vacuum Focusing in air

12. Angle of the ellipse after filament

13. Polarization study of the focused beam in air QWP Grazing plate Rotating polarizer cube xx Ellipticity 9mJ -60fs-filament in air Ellipticity change at focus vs energy

14. Spatial profile of the polarization The polarization evolution varies across the beam profile due to the intensity distribution. Measuring polarization profile of the beam provides an insight to nonlinear interaction within a light filament Angle of ellipse for selected colors of the beam perifery

15. L. V. Keldysh, Sov. Phys. JETP 20, 1307 (1965). "Ionization in the field of a strong electromagnetic wave" if γ<1, multiphoton ionization can be approximated as tunnelling. U p energy of the classical-like motion of an electron in IR field U p =6 eV for λ=800nm; I=10 14 W/cm 2 Multi PhotonTunneling Tunnel ionization

16. 16 Electron ionization -- linear polarization Strong Field Approximation

17. Electron ionization -- Circular polarization For 800nm light and I~10 14 W/cm 2, In tunneling with circularly polarized light the field is always on. The velocity distribution of electrons has a donut distribution where the radius of the donut is defined by drift velocity and the thickness by quantum tunneling width. L.Arissian PRL,105, 133002 (2010)

18. Equation of motion Drude model Is electron density enough for knowing the index? Bond electronFree electron

19. Traditional index motion response propagation

20. Radiation of expanding bobble

21. Pondermotive gradient Conservation of momentum and energy C.Smeenk,L.Arissian PRL,106, 193002 (2011) Partition of momentum in strong field ionization

22. - Change of sign in Ar current ….circular versus linear - Amplitude of the signal in N2, ten time higher circular versus linear - No change in circular radiation with pressure for both Ar and N 2 - Competition between laser force and Coulomb wake force is more observed in linear light and Ar, for its lower cross section (5-10 times) Polarization dependent current in a plasma channel B Zhao…,L.Arissian PRL,106, 255002 (2011)

23. Fluorescence 337 as a function of polarization  f=300cm PMT Filter

24. 3 mJ 5 mJ 7 mJ 9 mJ 3 mJ 5 mJ 7 mJ 9 mJ Simulation of nonlinear pulse propagation A.Couarion Linear Circular

25. Conclusion Filamentation at its core is a strong field ionization process Polarization evolution can be used to explore the nonlinear interaction

26. Thank you

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