1. Two-Color I-SASE A.Marinelli, J. Wu, C. Pellegrini LCLS2 Meeting SLAC 1/30/2013

2. It has been suggested that a wide, 1-2% wide X-ray spectrum, might be an advantage for coherent diffraction imaging. A possible alternative is a two colors spectrum with narrow lines separated by 1-2%. A two color spectrum has recently been observed at LCLS while doing the iSASE studies. A dedicated 2-color iSASE experiment is being planned two colors 1/8/13 Diffraction imaging

3. Science with 2-Color iSASE Soichi Wakatsuki et al. Use of 2-color iSASE for SAD/MAD Phasing on XPP Two proposals already submitted Request for separation from 0.1% to 2%

4. Science with 2-Color iSASE Soichi Wakatsuki et al. Use of 2-color iSASE for SAD/MAD Phasing on XPP Two proposals already submitted Request for separation from 0.1% to 2% ~within FEL bandwidth

5. Proof of Principle Demonstration of iSASE Proof of principle demo: use detuned undulators at LCLS Delay line introduces longer coherence legnth

6. Machine layout: First 5 undulator sections on-resonant two color From 6 th on, even number: 6, 8, …, 30, and 32 largely detuned (can either be random or form a separate spectrum line  two color) From 6 th on, odd number: 7, 9, …, 31, and 33 on resonant Perform proof-of-principle experiment on LCLS for an improved SASE (iSASE) Electron bunch: 150 pC, compressed to 3 kA 8.45 keV FEE HXSSS 13.825 GeV electron energy two colors 1/8/13 LCLS iSASE experimental setup

7. Experimental Results Observed a reduction of linewidth by ~ 3.4

8. Two-Color iSASE Alternating K value-> One wavelength gains, the other is delayed-> Two colors with narrower bandwidth than SASE

9. Observed During iSASE Experiment

10. Line separation not consistent with detuning!

11. 1-D Theory Effect of high-gain FEL on the collective variables described by 3x3 matrix

12. Two Color I-SASE Define detuning  with respect to average resonant frequency (  )/2

13. Two Color I-SASE For large detuning:

14. Two Color I-SASE For large detuning: Undulator dispersion Undulator delay Equivalent to iSASE transfer matrix…

15. Example: Delta = 6 Sidebands appear at the frequency given by undulator periodicity. Relative intensity of the 4 peaks strongly dependent on Delta (weaker dependence for longer periodicity) Period = 2 Lg Period = 4 Lg Period = 8 Lg

16. Genesis Simulations Genesis simulations for ideal beam show same trends. The sideband separation is consistent with our understanding. Can we control this structure? DeltaK = 0.6%DeltaK = 0.9% DeltaK = 1.1%

17. Power VS Time

18. Gain Curve

19. Comparison with Alberto’s Experiment 2-color experiment at LCLS worked beautifully… What does our method do that hasn’t been done yet? 1)Perfect synchronization of two colors (good for imaging) BUT no tunable delay (actually tunable within slippage length...) 1)Each color has the i-SASE bandwidth (tunability within the SASE bandwidtdh...). 1)Control of sidebands allows extra degree of freedom on the spectral structure.

20. Comparison Similar Power Level (a little higher for the two undulator method)

21. A Few Words on LCLS2 -The greater range of tunability of LCLS2 allows even more flexibility in tayloring the spectrum. -Mimic ~10% bandwidth with more than two colors?

22. Open Questions 1) Are we over-complicating the analysis? The chain matrix multiplication method is direct but does not give intuitive closed form formulae Maybe some more intuitive picture is possible… 2) In practice, how much control do we have over the sidebands for short undulator periodicity? Can we use them for fine-tuning of the spectrum within the SASE bandwidth?

23. Open Questions What happens with a realistic beam distribution? Working on GENESIS simuations right now… Experiment will tell us the answer! Experimental Plan: Study spectrum VS K separation looking for: 1)Wavelength separation VS Delta K 2)Sideband structure manipulation changing periodicity 3) XPP spectrometer for overall spectrum FEE spectrometer for single-shot study of sidebands