High harmonic generation in a large-volume capillary for seeding of free-electron lasers Siew Jean Goh

Outline Motivation High Harmonic Generation Setup Result Overview and summary

Why Seed a Free-Electron Laser ? Shorter FEL Wavelengths? E. Allaria et al, Nature Photonics Vol 6, pg 699–704 (2012)

High Harmonic Source for Seeding Single order pulse energy ~100 nJ Seed wavelength range (30-40 nm) High pulse energy stability (< 10 %) High pointing stability (< 20 % of beam size) Seed Beam 0.3 mm e-Beam 15 m Seeded Operation down to 5-6 nm

High Harmonic Setup

Large Capillary (Motivation) Assist phase matching with waveguiding Selective enhancement via pulse shaping Self-phase-modulation & self-compression Stabilize beam pointing by waveguiding Output scales with volume

Typical High Harmonic Spectrum Drive laser energy = 6.5 mJ, pressure: 4 mbar Spectrum determined by filter edge,cut-off and phase-matching

20 shots integrated beam profile Typical High Harmonic Beam Profile Near gaussian and elliptical Energy content Center of gravity Standard deviation  Beam pointing and divergence 20 shots integrated beam profile 5 mbar 1 mm Divergence (x-axis) = 2σx / L = 3 mm / 9 m = 0.3 mrad Excellent spatial quality at 4 - 6mbar

High Harmonic Energy From 20 consecutive measurements of 20 shots integrated beam profile

Energy Jitter   From 20 consecutive measurements of 20 shots integrated beam profile

Divergence L = 9 m From 20 consecutive measurements of 20 shots integrated beam profile

Pointing Stability From 20 consecutive measurements of 20 shots integrated beam profile

Harmonic Selective Enhancement Selective enhancement of 2.5 (at 37 nm)

Overview of Results Standard Capillary 150 mm; 1.0 mJ, 53 mbar (Ar) (100 x single shot) Large Capillary 508 mm; 6.5 mJ 6 mbar (Ar) (20 x 20 Shots) Seed Requirement FERMI@Elettra Wavelength 35 nm 32 nm 30 - 40nm Divergence 1.5 mrad (x) 1.6 mrad (y) 0.5 mrad (x) 0.4 mrad (y) < 10% Pointing Stability 6% (x) 17% (y) 11% (x) 9% (y) < 20% Energy Jitter 18 % 34 % Energy 0.2 nJ 0.6 nJ ~100 nJ

Output Energy Possible problems Reabsorption in differential pumping section Absorption in oxide layer on Al filters Absorption in carbon layer deposit on XUV camera Next steps Reduce gas flow, cleaning, absolute calibration Add amplitude shaping

Summary Large-volume capillary (d= 500 mm) Phase matching at 5 - 6 mbar Selective enhancement (2.5-fold at 37 nm) Beam pointing stability (~10%)

Thank you for your attention! Acknowledgement Acknowledgements Thank you for your attention! 17