High harmonics from gas, a suitable source for seeding FEL from vacuum-ultraviolet

1. Palaiseau - FRANCE 22/08/11 High harmonics from gas, a suitable source for seeding FEL   from vacuum-ultraviolet to soft X-ray region (XUV) G. LAMBERT guillaume.lambert@ensta.fr UMR 7639 http://loa.ensta.fr/

2. M.E. Couprie, M. Labat, O. Chubar Synchrotron Soleil, Gif-sur-Yvette, France D. Garzella, B. Carré CEA, DSM/SPAM, Gif-sur-Yvette, France T. Hara, H. Kitamura, T. Shintake, Y. Tanaka, T. Tanikawa SPring-8/RIKEN Harima Institute, Hyogo, Japan B. Vodungbo, J. Gautier, A. Sardinha, F. Tissandier, Ph. Zeitoun, S. Sebban, V. Malka LOA ENSTA-Paristech, Palaiseau, France J. Luning LCPMR, Paris C.P. Hauri Paul Scherrer Institute, Villigen, Switzerland M. Fajardo Centro de Física dos Plasmas, Lisboa, Portugal Thanks to JSPS LaserlabIntegrated Infrastructures Initiative RII-CT-2003-506350 TUIXS European project (Table top Ultra Intense XUV Sources) FP6 NEST-Adventure n.012843 European Research Council Paris ERC project 226424 UMR 7639 http://loa.ensta.fr/

3. XUV Free Electron Lasers (FEL) : SASE FLASH (2004, down to 4.1 nm), SCSS (2007, 50 nm), SPARC (2009, 160 nm)… SASE: Self Amplified Spontaneous Emission Accelerator λ, t -High number of photon : 1012 photons -Short pulse duration (sub ps) peak power (GW) -Relatively high repetition rate (tens Hz) -High wavelength tuning -Variable polarization -Good wavefront (Bachelard, PRL 106, 2011) -Good spatial coherence (Ischebeck, NIMA 507, 2003) very performing tool for user experiment but… 1

4. SASE limitations 157 158 159 160 161 162 163 164 165 -Weak gain at short wavelength, single pass long undulator (tens m) -Relatively important shot to shot variations: intensity, temporal/spectral profile jitter for pump-probe experiments limited temporal coherence (Saldin, Opt. Commun. 202, 2002) 1 0.8 0.6 Intensity (arb. unit.) 0.4 0.2 0 Wavelength (nm) 2

5. How to reduce/supress SASE limitations: “seeding fully coherent light” in XUV ? λ, t Previous demonstrations in IR with CO2 and Ti: Sa lasers, then in UV with crystals (Yu, Science 289, 2000) Accelerator External source Seeded λ, t -Coherent Improvement of the temporal coherence -Intense Decreasing of the saturation length => shorter undulator SASE About the same gain XUV radiation : Harmonics produced from gas (HHG) 3

6. Why proposing High Harmonics Generated in gas (HHG) ? Odd harmonics Rare gas ● Spatially and temporally coherent ● Relatively tunable ● Short pulse duration (10-100 fs) ● Conversion efficiency (10-5 to 10-7) ~ 100 nJ - nJ Lens Laser ~1014 W/cm2 Cut-off Number of photon -Limited energy per pulse Compared to SASE shot noise? Harmonic order 4

7. Direct seeding with HHG at 160 nm at SCSS: fundamental spectrum 1 0.8 0.6 0.4 0.2 0 SCSS Test Accelerator (Japan) at 150 MeV with 4.5 m long undulator sections (Lambert, Nature Physics 4, 2008) -High amplification -Regular and quasi-perfect Gaussian shape -Spectral width / ~5 -Pulse duration / ~20 Unseeded: 1 ps HHG: 50 fs Seeded: 50 fs SASE x 13.7 Seeded 2 μJ (40 MW) Intensity (Arb. Un.) HHG x 9270 Strong improvement of the temporal coherence/SASE 157 158 159 160 161 162 163 164 165 Wavelength (nm) 5

8. Non Linear Harmonic spectra 1 1 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 0 0 53.4 53.8 54.2 1 H5 -Odd and even harmonics from 2nd (80 nm) to 7th (23 nm) -Clear amplification -Regular and quasi Gaussian spectral shape -Spectral narrowing -Shorter pulse duration Improvement of the temporal coherence 0.8 0.6 Intensity (arb. un.) Unseeded 0.4 H6 H7 0.2 0 22 24 28 30 32 26 Wavelength (nm) H2 H3 Seeded: 4 nJ (75 kW) Seeded: 3 nJ (50 kW) Unseeded x 125 Intensity (arb. un.) Intensity (arb. un.) Unseeded 53 80 81 79.5 80.5 81.5 Wavelength (nm) Wavelength (nm) (Tanikawa, EPL 94, 2011) Seeded: 55 pJ (1 kW) Intense and coherent emission at short wavelength while E=150 MeV 6

9. Evaluation of the seed level requirement for observing coherent emission Eseed=88 pJ EFEL=12.2 nJ 3 2 1 0 3 2 1 0 3 EFEL=0.87 nJ Eseed=0 pJ 2 1 0 3 2 1.0 1 0.8 0 0.6 0.4 0.2 0.0 HHG seed Eseed=88 pJ For Eseed≥88 pJ: -Stable emission -Regular and quasi Gaussian spectral profiles Vertical position (mm) Eseed=14 pJ EFEL=1.4 nJ Very weak level of injection 88 pJ (160 nm) ―> 10 pJ (spatial overlapping) or ~ 200xPe, shot noise At 13 nm(Pe, shot noise<10 W) ―> Eseed < 0.7 nJ (200x10Wx10x35fs) Vert. pos. (mm) Eseed=88 pJ Eseed=0 pJ Eseed=14 pJ Normalized intensity (arb. un.) Seeding in XUV ! HHG Below 13 nm is a challenge! (Lambert, EPL 88, 2009) 159 163 164 160 161 162 Wavelength (nm) 8

10. Overview of the HHG seeded FELs (Giannessi, Proceedings FEL10 JACOW (2011) Labat WE0B3) (Togashi, Optics Express 19, 2011) 9

11. What has to be improved on HHG for seeding FEL in future? Harmonics properties relevant for seeding Already obtained -fs pulse duration -Full coherence -High repetition rate: kHz HH currently First MHz HH in xenon (J. Boullet et al. optics letters, 34, 1489 (2009)) To be improved -Intensity at short wavelengths -Tuneability (only odd HH): => need to considerably chirp the driving laser and/or change the gap of the undulator -Wavefront: diffraction limited beam (aberration-free) => need to drastically clip the IR or HH beam or use adaptive optics for IR or HH -Variability of the polarization -Stability of the shot to shot intensity Two colour mixing Keep the simplicity of the classical HHG setup 10

12. High order harmonics generated with a two-colour field ω Harmonics 2ω Noble gas Ti: Sa IR Filter ~1014 W/cm2 BBO crystal Lens (Lambert, NJP 11, 2009) Technical principle: Neon X 25 ω +2ω -increase of the number of photons -double harmonic content even types: 2x(2n+1) from 2w 2x(2n) from the mixing -redshift: 11

13. Harmonic spectra obtained with either ω or ω+2ω technique 104 103 102 101 He, ω He, ω +2ω Ne, ω Ne, ω +2ω Ar, ω Ar, ω +2ω Xe, ω Xe, ω +2ω 100 10 15 20 25 30 35 40 45 50 55 60 65 70 75 100 µm thick BBO crystal, and with the optimization parameters corresponded to ω: Eω<6 mJ, LC=7-9 mm and PG=30-35 mbar Al cut (x 0.5) (x 0.5) -Flat spectra (same intensity level for odd and even harmonics) (x 25) -Increase limited at high wavelengths due to an already relatively high efficiency for Xe and Ar Intensity (arb. un.) (x 100) => ω+2ω technique compensates the weak efficiency at short wavelengths Wavelength (nm) (Lambert, NJP 11, 2009) 12

14. Optimization of both flux and wavefront (Ar gas) 50 Iωand I2ωin 1014 W.cm-2 40 Iω~3.9 1 Energy per pulse (nJ) I2ω~2.9 Iω~4.4 30 I2ω~5.4 Iω~0.8 I2ω~1 20 30 Wavelength (nm) 0.5 λ l/5 rms l/17 rms l/6 rms 10 0 35 40 45 50 55 60 0 (Lambert, EPL 89, 2010) -iris clipping technique: change the focusing geometry/energy clean the major part of the distortions in the outer part of the beam: l to l/6 rms H18 100 mm thick BBO crystal H14 Φ=40 mm -ω (LC=8 mm and PG=30 mbar) to ω+2ω (LC=4 mm and PG=16 mbar) Φ=40 mm -very high increase on 2x(2n+1) type of even harmonics (50 nJ) due to strong blue/IR and distortions limited: l/5 rms Φ=20 mm Φ=20 mm Iω~1.2 H22 -iris clipping: limited decrease of intensity But distortions about l/17 rms: First aberration-free high harmonic beam H19 H17 H21 H23 H25 H27 H15 13

15. Then next? Already obtained -fs pulse duration -Full coherence -High repetition rate: kHz to MHz soon -Intensity at short wavelengths -Tuneability:both odd and even harmonics Use parametric amplifier (1.2-1.5 mm) -Wavefront: aberration-free beam -Simple system To be improved -Variability of the polarization -Stability of the shot to shot intensity? 15

16. Circularly polarized HH -Using circular IR beam -Two step setup: linear IR beam + polarizer (Vodungbo, Optics Express 19, 2011) 16

17. User applications in XUV: SASE-FEL vs HH In XUV performances are close: weak flux harmonics weak temporal coherence Single shot coherent diffraction imaging of nano-object (Ravasio et al. PRL 103 (2009) 32 nm, 1μJ, 20 fs Reconstructed image with 119 nm resolution 17

18. Pump-probe experiments MFM Co M2,3 edge at 60 eV a Aligned magnetic domains Natural synchronization between Laser and HH Coherent diffraction imaging of magnetic domains (Vodungbo, EPL 94, 2011): 1200 s D q~ λD/a -Magnetic domain orientation: 45°+- 10° -Width distribution of magnetic domains: 65 nm +- 5 nm 18

19. Ultra-fast demagnetization Integrated density gives magnetization : I ~ M2 -much shorter time scale -better temporal resolution for HH? And/or due to XFEL at 800 eV (L edge) (Boeglin, Nature 465, 2010) 19

20. Thank you for your attention

21. How to perform a HHG seeding experiments ? • Generate HHG with as much as possible photons • Refocus HHG at the electron beam size inside the undulator for strong interaction • Align precisely HHG beam on the undulator axis • Tune HHG wavelength with FEL one • Synchronize ebeam and HHG below ps time scale HHG Gas Laser Refocusing system Various undulator configurations Spectrometer device e- Electron source Chicane 5

22. Stabilization of the FEL wavelength 1 162.8 162.8 SASE 0.8 162.0 162.0 0.6 161.2 161.2 Intensity (a. u.) 0.4 Wavelength (nm) Wavelength (nm) 160.4 160.4 0.2 159.6 159.6 0 1 Seeded 1 ~300 s 0.8 0.8 0.6 0.6 Intensity (a. u.) Intensity (arb. un.) 0.4 0.4 0.2 0.2 0 0 50 60 70 80 90 100 157 158 159 160 161 162 163 164 165 Wavelength (nm) Data file number 1 ~60 s 0.8 0.6 0.4 0.2 0 2 4 6 8 10 12 14 16 18 20 Data file number 7

23. Stabilization of the FEL wavelength 162.8 162.8 162.0 162.0 161.2 161.2 Intensity (a. u.) Wavelength (nm) Wavelength (nm) 160.4 160.4 159.6 159.6 1 ~300 s 0.8 0.6 Intensity (a. u.) 0.4 0.2 0 50 60 70 80 90 100 Data file number 1 ~60 s +-37% 0.8 161.03 nm ± 0.63 nm rms 0.6 -λ stabilized by a factor of 6 -Still important intensity variation (mainly due to synchronization trouble) 0.4 0.2 0 2 4 6 8 10 12 14 16 18 20 Data file number +-57% 161.10 nm ± 0.10 nm rms 7

24. High order harmonics generated with a two-colour field ω Harmonics 2ω Noble gas Ti: Sa IR Filter ~1014 W/cm2 BBO crystal HHG Lens x WE=ex.Esinwt Ip Tunnel ionization t~T/4 Oscillation in the laser field t~3T/4 Radiating recombination t~T Initial state t~0 (Lambert, NJP 11, 2009) Neon Theoretical and technical principles: X 25 ω +2ω Semi-classical model in three steps: -increase of the number of photons -double harmonic content even types: 2x(2n+1) from 2w 2x(2n) from the mixing -redshift: 11

25. General set-up Transmission grating (2000 lines/mm) CCD Camera Iris Spectrometer Hole array CCD camera Aberrated spot centroid position F Dy Reference spot centroid position Reference flat wave front Aberrated wavefront Wavefront sensor L BBO crystal, (100 mm or 250 mm thickness) Aluminium filters (200 nm thickness) Spherical multilayer mirror 800 nm 1 kHz < 7 mJ 35 fs Lens, f=1.5 m Calibrated XUV photodiode CCD Camera Grid Gas cell (4 to 7 mm long) Wavefront sensor F = Dy/L

26. Cleaning the distortions with the 2nd harmonic generation Wavefront sensor Filter HH footprint sizes HH source sizes From ω From ω+2ω From ω From ω+2ω 0 1.73 3.47 0 0.5 1 0 0.5 1 A. U. A. U. A. U. 1.4 time smaller for V and H sizes IR beam wavefront Waist ratio between ω and 2ω: Harmonics from ω+2ω 2ω ω Gas cell BBO iris

27. Summary of wavefront optimization 1 ω, deform. mirror (52 em act.), Ф=15 mm λ/10 rms 0.5 λ l/5 rms l/17 rms l/6 rms RMS (0.100λ), PV (0.483λ) 10 5 Vertical dimension (mm) 0 -5 (4) -10 0 -10 -5 0 5 10 Horizontal dimension (mm) ω,Φ=20 mm ω+2ω,Φ=40 mm λ=32 nm (ω) to 44 nm (ω+2ω) ω+2ω,Φ=20 mm

28. (a) λ/2 waveplate BBO crystal (100 μm thickness) Aluminium filters (200 nm thickness) SiO2 flat mirror 45° incidence B4C/Mo/Si flat mirror Lens, f=1.5 m V V V 2ω H H H ω 800 nm 1 kHz < 7 mJ 35 fs Spherical multilayer mirror Transmission grating (2000 lines/mm) Gas cell CCD Camera Iris Optical system (b) (c) ω 2n+1 2ω, Vert. Pol. Φ2n+1 2n HHG from ω+2ω Φ2n ω, Hor. Pol.

29. 2 ω 1.6 1.2 Intensity (1014 W. cm-2) 0.8 2ω 0.4 -80 -60 -40 -20 0 20 40 60 0 Time (fs) -variation of polarization between odd and even harmonics: Higher for longer wavelengths -variation of polarization from one order to another Aluminium filter

30. Perspectives of the two-colour HHG for seeding of FEL 100 Ar, ω +2ω Al cut 10 Ar, ω Energy per pulse (nJ) Ne, ω +2ω 1 Estimation of the Ne spectra content: below 17 nm at 13 nm 0.1 10 15 20 25 30 35 40 45 50 55 60 Wavelength (nm) dt 1 ω Intensity (a. u.) 2ω Δt2ω 0.5 Time (fs) 0 -60 -30 0 30 60 -80 nm-17 nm: intense XUV harmonic signal Ar(ω+2ω) intensity increase for 1 over 2 even harmonics Ne (ω+2ω) intensity about Ar (ω)intensity (typical reference) -13 nm: Ne (ω +2ω) about 0.3 nJ (Lambert, EPL 88, 2009) ~ 200 x PSASE, noise at 13 nm (PSASE, noise~ 10 W) => Eseed ~ 0.7 nJ (200 x 10 W x 35 fs) -Intensity could have been more optimized with more energy and longer focusing -Only relative control on the SHG/HHG ◘ I2w/Iw ok ◘ dt =18 fs /100 μm not ok ◘ Δt2w/Δtw not ok 14