1. Relativistically oscillating plasma surfaces : High harmonic generation and ultrafast plasma dynamics Brendan Dromey ICUIL 26 Sept – 1 Oct Watkins Glen NY Brendan Dromeyb.dromey@qub.ac.uk

2. Acknowledgements Brendan Dromeyb.dromey@qub.ac.uk Experiments:PIC-Simulations: R. Hörlein Y. Nomura D. Kiefer P. Heissler G. D. Tsakiris S. Rykovanov Max Planck Institute for Quantum Optics IESL, FORTH, Heraklion Crete: P. Tzallas D. Charalambidis Queens University Belfast: M. Yeung D. Adams M. Geissler M. Zepf ICUIL 26 Sept – 1 Oct Watkins Glen NY LANL, Trident D. Jung B. M. Hegelich STFC Central Laser Facility P. Foster C. Hooker D. Neely P. Norreys

3. Outline Low and high contrast interactions High order harmonic generation (HOHG) from solids keV harmonic generation Role of surface roughness – ultrafast laser driven plasma dynamics Divergence of HOHG Novel results for HOHG transmitted through thin foils scaling in the relativistic limit b.dromey@qub.ac.uk ICUIL 26 Sept – 1 Oct Watkins Glen NY Brendan Dromey

4. Contrast in a laser system Brendan Dromeyb.dromey@qub.ac.uk Slide courtesy of R. Marjoribanks ICUIL 26 Sept – 1 Oct Watkins Glen NY

5. Contrast improvement in a laser system Brendan Dromeyb.dromey@qub.ac.uk AR coated Contrast increased by ~ 10 2 per plasma mirror used 10 14 to 10 15 Wcm -2 Plasma mirror ICUIL 26 Sept – 1 Oct Watkins Glen NY

6. Petawatt class interactions Brendan Dromeyb.dromey@qub.ac.uk Andor CCD detector Target – CH (5-10 nm rms) Double plasma mirror Incident laser pulse: f 3 cone Vulcan Petawatt at RAL: ~600J in 500fs ~ 1053nm 1200 lines per mm flatfield grating Gold collection mirror ICUIL 26 Sept – 1 Oct Watkins Glen NY

7. Low Vs high contrast Brendan Dromeyb.dromey@qub.ac.uk Spectrum with plasma mirror – High harmonic generation, scaling in the relativistic limit B. Dromey et. al., Nature Physics, 2, 456 (2006) Spectrum with no plasma mirror 7mm 17nm ~ 2nm ICUIL 26 Sept – 1 Oct Watkins Glen NY

8. Relativistically oscillating plasmas Brendan Dromeyb.dromey@qub.ac.uk The target surface is highly ionised by the leading edge of the pulse – becomes rapidly over dense (reflecting to incident radiation) The collective electron motion created by the incident electromagnetic wave can be considered as an oscillating mirror Incident pulse Reflected pulse Oscillating critical density surface Illustration from George Tsakiris New Journal Physics 8, 19, 2006 ICUIL 26 Sept – 1 Oct Watkins Glen NY

9. Einstein's Relativistic Doppler effect - 4  2 Oscillatory extension to Relativistic Doppler effect γsγs t´ vsvs c c vsvs Universal spectrum Extended Roll-over n max  8 1/2  3 T. Baeva, S. Gordienko, A. Pukhov, Phys. Rev. E, 74, 046404 (2006) Relativistic Spiking Brendan Dromeyb.dromey@qub.ac.uk ICUIL 26 Sept – 1 Oct Watkins Glen NY = n -2.66

10. Important properties of ROM Brendan Dromeyb.dromey@qub.ac.uk Phase locked to driving laser – no phase matching required Both odd and even orders generated Generation process saturates in the relativistic limit High conversion efficiency – scaling as n -2.66, where n is harmonic order Harmonic width greater than separation for keV energies Rapid scaling to high orders with driving laser intensity Filter to obtain train of attosecond pulses No chirp ICUIL 26 Sept – 1 Oct Watkins Glen NY

11. Coherent wake emission Brendan Dromeyb.dromey@qub.ac.uk Plexiglass Target (Density ~1.3 g/cm^3): Glass Target (Density ~2.6 g/cm^3) : 111312 14 17 15 16 111312 14 15 ICUIL 26 Sept – 1 Oct Watkins Glen NY Brunel electrons

12. Relativistic plasma harmonics – salient results Brendan Dromeyb.dromey@qub.ac.uk ~p~p 26 24 22 20 18 16 14 Harmonic order (n) ROM Individual pulse duration: 900  400 as Attosecond Phase Locking Diffraction limited performance From ‘Y. Nomura et al, Nature Physics, 5, 124 - 128 (2009) From ‘B. Dromey et al, Nature Physics, 5, 146 - 152 (2009) Exceptional coherence properties of the driving laser transferred to the XUV ICUIL 26 Sept – 1 Oct Watkins Glen NY

13. Petawatt class interactions Brendan Dromeyb.dromey@qub.ac.uk Image plate detector Target – CH (5-10 nm rms) Double plasma mirror Incident laser pulse: f 3 cone Vulcan Petawatt at RAL: ~600J in 500fs ~ 1053nm Mica crystal, Von Hamos geometry ICUIL 26 Sept – 1 Oct Watkins Glen NY

14. ROM harmonics – Petawatt class Brendan Dromeyb.dromey@qub.ac.uk keV ROM harmonics and the efficiency roll-over B. Dromey et al., Phys. Rev. Lett. 99, 085001 (2007) 10 1 10 -1 10 -2 Intensity/arb. units Normalised at 1200 th order Harmonic order, n 15003000 a) (1.5±.3)  10 20 Wcm -2 b) (2.5±.5)  10 20 Wcm -2 Photon Energy, keV 20002500 1770 2360 2950 3530 p=2.8 p=2.4 P rel =2.55 (+0.25, -0.15) na max > 2600 nb max >3000 Intensity dependent rollover Focused Int P rel   n -p ICUIL 26 Sept – 1 Oct Watkins Glen NY

15. How can we see keV harmonics? Brendan Dromeyb.dromey@qub.ac.uk DfDf Surface roughness - Fourier analysis Angstrom wavelength lengths beamed from nm roughness targets? ICUIL 26 Sept – 1 Oct Watkins Glen NY

16. Motion under the influence of normally incident, linearly polarized EM wave, bound to an immobile ion background via charge separation fields 4 cycles FWHM Gaussian pulse, a o = 10, n e = 400n c Density gradient from 1-D PIC, same parameters Electron capacitor model Brendan Dromeyb.dromey@qub.ac.uk Complete discussion given in: Rykovanov et al arXiv:0908.3134v2 [physics.plasm-ph]arXiv:0908.3134v2 ICUIL 26 Sept – 1 Oct Watkins Glen NY

17. Brendan Dromeyb.dromey@qub.ac.uk  L =800nm, 4 cycle pulse, h = 40nmm, a0 =5 (corresponds to > 10 19 Wcm -2 ) Snap shots from Simulation – over a single cycle in the rise of the pulse Ultrafast plasma dynamics: 2-D PIC simulations Complete discussion given in: Rykovanov et al arXiv:0908.3134v2 [physics.plasm-ph]arXiv:0908.3134v2 h ICUIL 26 Sept – 1 Oct Watkins Glen NY

18. Brendan Dromeyb.dromey@qub.ac.uk 23 24 25 26 22 21 20 19 18 17 16 15 14 Grating Au Mirror Detector HOHG Source Astra laser at RAL: 10Hz ~1.5J in 40fs ~ 800nm Astra at RAL: 10Hz ~1.5J in 40fs ~ 800nm Off-axis emission CWE only On-axis emission - CWE and Rom O- axis emission - Rom only ICUIL 26 Sept – 1 Oct Watkins Glen NY

19. Insensitivity to surface roughness Brendan Dromeyb.dromey@qub.ac.uk From ‘B. Dromey et al, NATURE Physics, 5, 146 - 152 (2009) 22 20 18 16 Harmonic Order 37 35 33 31 29 27 25 23 Counts (  10 4 ) 2 1 0.5 1.5 Harmonic Order x y  rms <1nm  rms ~18nm 38 Spectra same to within 1 standard deviation for factor of >10 increase in roughness ICUIL 26 Sept – 1 Oct Watkins Glen NY

20. Divergence of HOHG Brendan Dromeyb.dromey@qub.ac.uk Harmonic Spectra: total power emitted 10 1 10 -1 10 -2 Intensity/arb. Units Normalised at 1200 th order Harmonic order, n 15003000 a) (1.5±.3)  10 20 Wcm -2 b) (2.5±.5)  10 20 Wcm -2 Photon Energy, keV 20002500 1770 2360 2950 3530 P rel =2.55 (+0.25, -0.15) ICUIL 26 Sept – 1 Oct Watkins Glen NY

21. Harmonic divergence Brendan Dromeyb.dromey@qub.ac.uk Flat surface Harmonics emitted with intrinsic divergence If all orders diffraction limited - expect a much flatter spectrum θLθL θ L /n Diffraction limited peformance would suggest  harmonic ~  Laser /n   harmonic ~10 -4 rad for keV harmonics. ICUIL 26 Sept – 1 Oct Watkins Glen NY

22. Uniform harmonic divergence Brendan Dromeyb.dromey@qub.ac.uk Curved surface Harmonics emitted with divergence given by the curved surface D -All orders identical divergence -Beam still focusable to diffraction limit for spherically bent surface. ICUIL 26 Sept – 1 Oct Watkins Glen NY

23. Divergence measurements Brendan Dromeyb.dromey@qub.ac.uk -1nm 1nm a) <1nm rms i) Orders 17-39 Spectrometer configuration Recorded spectra Angle  (mrad) 39 th (~20.5nm ) 20th (~40nm) 19mrad 1/e 2 a) b) -60 -40-2002040 60 0.1 0.3 0.5 0.7 1.1 20 10 30 40 Angle  (mrad) Wavelength (nm) CWE orders ROM orders Intensity, arb. units Diffraction limited divergence 20 25 30 35 40 45 50 B. Dromey et al, Nature Physics, 5, 146 - 152 (2009) ICUIL 26 Sept – 1 Oct Watkins Glen NY

24. ROM in transmission: H. George, et al., NJP, 9, 113028 (2009) Experimental results: K. Krushelnick, et al., PRL, 100, 125005, (2008). ROM harmonics in transmission Brendan Dromeyb.dromey@qub.ac.uk ICUIL 26 Sept – 1 Oct Watkins Glen NY

25. ROM harmonics in transmission Shortpulse-Beam: 500fs, 125J, 250 TW (1054nm) Trident laser - Los Alamos national labs Brendan Dromeyb.dromey@qub.ac.uk ICUIL 26 Sept – 1 Oct Watkins Glen NY

26. ROM harmonics in transmission Brendan Dromeyb.dromey@qub.ac.uk 23 rd 33 rd Detector position 1Detector position 2 17nm Al L-edge 61 st 53 rd 43 rd 26nm45nm ICUIL 26 Sept – 1 Oct Watkins Glen NY Raw data from CCD

27. Brendan Dromeyb.dromey@qub.ac.uk ICUIL 26 Sept – 1 Oct Watkins Glen NY ROM harmonics in transmission Harmonic orders 24 - 60 Harmonic intensity normalised to the 33 rd harmonic 125 and 200nm Diamond like carbon Recall from the theory of relativistic spikes efficiency scaling is expected as n -2.66

28. ROM harmonics the full picture Brendan Dromeyb.dromey@qub.ac.uk ICUIL 26 Sept – 1 Oct Watkins Glen NY B. Dromey et. al., Nature Physics, 2, 456 (2006) Harmonic orders 24 - 60 Harmonic intensity normalised to the 33 rd harmonic Harmonic intensity normalised to the 238 rd harmonic Ultrathin thin foil at solid density

29. ROM harmonics for radial density profiling Brendan Dromeyb.dromey@qub.ac.uk ICUIL 26 Sept – 1 Oct Watkins Glen NY Red triangles on Figure For more detail: Rainer Hoerlein Thursday 11:00am Experimental geometry 200nm 80nm

30. Summary Brendan Dromeyb.dromey@qub.ac.uk Very high harmonics possible from the relativistic plasma medium Diffraction limited performance and attosecond phase locking Ultrafast laser driven plasma dynamics – allows beamed keV radiation Target denting – possible to shape targets to control divergence Transmitted HOHG – novel ROM source Use as an ultrafast broadband density diagnostic ICUIL 26 Sept – 1 Oct Watkins Glen NY

31. Brendan Dromeyb.dromey@qub.ac.uk Ultrafast broadband density diagnostic Single foil 125nm, Slow drop in signal to higher orders (~relativistic limit scaling) With Secondary foil (80nm) Plasma Absorption, up to plasma frequency With secondary foil (200nm) Strong Carbon absorption 28 th 23 rd 45nm 30 nm O 2 17.1nm line in second order ICUIL 26 Sept – 1 Oct Watkins Glen NY