Relativistically oscillating plasma surfaces : High harmonic generation and ultrafast plasma dynamics Brendan Dromey ICUIL 26 Sept – 1 Oct Watkins Glen NY Brendan

Acknowledgements Brendan 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

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 ICUIL 26 Sept – 1 Oct Watkins Glen NY Brendan Dromey

Contrast in a laser system Brendan Slide courtesy of R. Marjoribanks ICUIL 26 Sept – 1 Oct Watkins Glen NY

Contrast improvement in a laser system Brendan AR coated Contrast increased by ~ 10 2 per plasma mirror used to Wcm -2 Plasma mirror ICUIL 26 Sept – 1 Oct Watkins Glen NY

Petawatt class interactions Brendan 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

Low Vs high contrast Brendan 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

Relativistically oscillating plasmas Brendan 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

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, (2006) Relativistic Spiking Brendan ICUIL 26 Sept – 1 Oct Watkins Glen NY = n -2.66

Important properties of ROM Brendan 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

Coherent wake emission Brendan Plexiglass Target (Density ~1.3 g/cm^3): Glass Target (Density ~2.6 g/cm^3) : ICUIL 26 Sept – 1 Oct Watkins Glen NY Brunel electrons

Relativistic plasma harmonics – salient results Brendan ~p~p Harmonic order (n) ROM Individual pulse duration: 900  400 as Attosecond Phase Locking Diffraction limited performance From ‘Y. Nomura et al, Nature Physics, 5, (2009) From ‘B. Dromey et al, Nature Physics, 5, (2009) Exceptional coherence properties of the driving laser transferred to the XUV ICUIL 26 Sept – 1 Oct Watkins Glen NY

Petawatt class interactions Brendan 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

ROM harmonics – Petawatt class Brendan keV ROM harmonics and the efficiency roll-over B. Dromey et al., Phys. Rev. Lett. 99, (2007) Intensity/arb. units Normalised at 1200 th order Harmonic order, n a) (1.5±.3)  Wcm -2 b) (2.5±.5)  Wcm -2 Photon Energy, keV 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

How can we see keV harmonics? Brendan DfDf Surface roughness - Fourier analysis Angstrom wavelength lengths beamed from nm roughness targets? ICUIL 26 Sept – 1 Oct Watkins Glen NY

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 Complete discussion given in: Rykovanov et al arXiv: v2 [physics.plasm-ph]arXiv: v2 ICUIL 26 Sept – 1 Oct Watkins Glen NY

Brendan  L =800nm, 4 cycle pulse, h = 40nmm, a0 =5 (corresponds to > 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: v2 [physics.plasm-ph]arXiv: v2 h ICUIL 26 Sept – 1 Oct Watkins Glen NY

Brendan 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

Insensitivity to surface roughness Brendan From ‘B. Dromey et al, NATURE Physics, 5, (2009) Harmonic Order Counts (  10 4 ) 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

Divergence of HOHG Brendan Harmonic Spectra: total power emitted Intensity/arb. Units Normalised at 1200 th order Harmonic order, n a) (1.5±.3)  Wcm -2 b) (2.5±.5)  Wcm -2 Photon Energy, keV P rel =2.55 (+0.25, -0.15) ICUIL 26 Sept – 1 Oct Watkins Glen NY

Harmonic divergence Brendan 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

Uniform harmonic divergence Brendan 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

Divergence measurements Brendan -1nm 1nm a) <1nm rms i) Orders Spectrometer configuration Recorded spectra Angle  (mrad) 39 th (~20.5nm ) 20th (~40nm) 19mrad 1/e 2 a) b) Angle  (mrad) Wavelength (nm) CWE orders ROM orders Intensity, arb. units Diffraction limited divergence B. Dromey et al, Nature Physics, 5, (2009) ICUIL 26 Sept – 1 Oct Watkins Glen NY

ROM in transmission: H. George, et al., NJP, 9, (2009) Experimental results: K. Krushelnick, et al., PRL, 100, , (2008). ROM harmonics in transmission Brendan ICUIL 26 Sept – 1 Oct Watkins Glen NY

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

ROM harmonics in transmission Brendan 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

Brendan ICUIL 26 Sept – 1 Oct Watkins Glen NY ROM harmonics in transmission Harmonic orders 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

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

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

Summary Brendan 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

Brendan 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 nm line in second order ICUIL 26 Sept – 1 Oct Watkins Glen NY