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

2. Outline Motivation High Harmonic Generation Setup Result
Overview and summary

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

4. 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

5. High Harmonic Setup

6. 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

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

8. 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

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

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

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

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

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

14. 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
Wavelength
35 nm
32 nm nm
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

15. 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

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

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