1. 1 Interaction of a 2.45GHz wave with a plasma filament driven by femtosecond laser in atmospheric air Interaction of a 2.45GHz wave with a plasma filament driven by femtosecond laser in atmospheric air Yves-Bernard André Bernard Prade (André Mysyrowicz’s group) Jean Larour Copenhagen, DK 7-8 April 2014 Jean.larour@lpp.polytechnique.fr 33rd Panel Business Meeting Week AVT 190 final year

2. 2 Objectives  Coupling a HF wave with a laser filament  Injecting µ-wave energy into the filamentary plasma  Depositing into the plasma an energy much higher than the laser pulse one  The whole in a fast pulsed regime

3. 3 Recall of the principles  Plasma sustained by surface waves traveling at the edge of the plasma and releasing energy inside the evanescence length  Surfatron® applicator  Proven on large bore (1cm to 1’’) tube for gas flow  liter.mn -1  Dependent on long-life (µs) of ionizable excited species

4. 4 CST Microwave Studio® simulation 1212  =1  =5- 10 Excitation of the rumbatron : capacitive or inductive (at 2,4GHz or in X band) Materials : perfect metal, sapphire, ceramics Plasma : coaxial tubes with complex permittivities (Drude model)  ’  –  p       ’’ = (  p        p  = n e   m e    plasma frequency Modelling the coupling cavity

5. 5 CST Microwave Studio® simulation E field distribution (instantaneous)

6. 6 CST Microwave Studio® simulation Low coupling

7. 7 CST Microwave Studio® simulation poor coupling

8. 8 CST Microwave Studio® simulation Tendency to a weak coupling with reduced diameter Not favoured by a unique filament (diam 100µm) Not favoured by a very short lifetime filament (1ns) Possibly favoured by a bundle of 100 – 400 filaments (within diam. 4mm)  Exploring the option of a filament close to the launching zone

9. Surfatron® device coaxial cable Movable capacitive antenna Gas inlet Plunger Steel knife-edge Launching slot discharge glass tube Magnetron 2.45 GHz 300-600W cw Coaxial cable 1kV Brass cavity Triggering spark Surfatron® applicator Dissymetric Creating a localized excess of E z at the muzzle NOT a leak of µ-wave through the aperture Exploiting long-life ions and excited species z axis

10. 10 Surfatron® device coaxial cable Movable capacitive antenna Gas inlet Plunger Steel knife-edge Launching slit (typ 1mm) discharge glass tube Magnetron 2.45 GHz 300-600W cw Coaxial cable 1kV Brass cavity Triggering spark E 0.sin  t E z =k.sin  t U 0.sin  t E 0.sin  t E z =k.sin  t

11. 11 Spark-triggered surfatron® device coaxial cable Movable capacitive antenna Gas inlet Plunger Steel knife-edge Launching slit Plasma discharge glass tube Magnetron 2.45 GHz 300-600W cw Coaxial cable 1kV Brass cavity Triggering spark 40mm Pre-plasma in optimal position at the gap level, ready to receive µ-waves. Glass tube is the one broken by excess heating.

12. End of the 8-mm pyrex tube Air ignition is triggered by a spark at the end of a miniature coax @1500V, in air flow at 1bar with 2.45GHz magnetron operation @ 600W, after 3s. Plasma torch length is around 5cm. Colors come from copper (braid) and fluor (PTFE cable dielectric) Air flow plasma 5-cm long 6-mm diam. plasma torch Spark-triggered surfatron® device

13. 13 Coaxial cable Capacitive coupling antenna Gas inlet Plunger Knife edge Lauching slit Filamentary Plasma with starting point chosen in the launching zone SiO 2 tube Magnetron 2.54 GHz 300-600W cw Clear hole for fs-Laser propagation NO visual evidence of a plasma modification Supplementary diagnostics are needed Brass cavity Adapted Surfatron® for fs-laser coupling

14. 14 Supplementary diagnostics Usual tools for studying fs-filaments : side-on emission at 12 GHz side-on emission at 91 GHz radiofrequency detection side-on luminescence at 337 nm and at 391 nm electrical diagnostic Surfatron® F = 2 m THz detectors UV-Vis spectrometer Electrical diagnostic LEAT antenna fs laser z

15. 15 Position : 3 cm black : 0 Watt green : 100 watt red : 200 watt Position : 8 cm black : 0 Watt green : 100 watt red : 200 watt Single shot laser Effect of HF application on 12 GHz detection Time (s)

16. 16 Black : 0 Watt Green : 100 Watt unstable Red : 200 Watt 1 seul tir laser Effect of HF application on 91 GHz detection Peak 0.04 V Dt 1/2 8ns integral 0.32V.ns Time (s) 0.00E+0002.00E-0084.00E-0086.00E-008 -0.05 -0.04 -0.03 -0.02 -0.01 0.00 VOLTS TEMPS Time (s) Single shot For 200 Watt, hint of a continuum

17. 17 Black : 0 Watt Red : 200 watt Single shot laser Antenna from L.E.A.T. lab Laser + 200 Watt 200 shots Time (s)

18. 18 Side-on luminescence spectroscopy F1 = 75mmHV PM= - 1500VF2 = 200mm 17cm10cm18cm monochromator photomultiplier Lambda nm 337 358 391

19. 19 Sensors 2011, 11, 32-53; doi:10.3390/s110100032 Femtosecond Laser Filamentation for Atmospheric Sensing Huai Liang Xu and See Leang Chin (U. Laval) Long pulse 200ps Short pulse 42fs

20. 20 Side-on line luminescence 337 nm 300 Tirs N 2 * 391 nm 100 Tirs N 2 + HV PM=- 1500 Volt 100 shots 300 shots

21. 21 One fs filament cannot provoke plasma spike development with a 0.6kW 2.45GHz applicator and relatively large difference of radii. For HF power up to 300W some observations were performed :  emission of waves : the detectors at 12 GHz and 91 GHz and a THz antenna detect an augmented signal when laser + HF  so far, it is not possible to discriminate the 2.45 GHz surface waves  Luminescence : two lines were tested, corresponding to different emission mechanisms, but with intensity sensitive to the electron density. No evidence of modification.  Electrical diagnostics are in progress Summary

22. 22

23. 23

24. 24