Seeding of free electron lasers by various techniques A. Meseck

2 CLASSE-Seminar Nov A. Meseck ORS Collaborators: Stockholm University: Peter Salen, Mathias Hamberg, Mats Larsson Uppsala University: Volker Ziemann, Gergana Angelova-Hamberg DESY: Holger Schlarb, Florian Löhl, E. Saldin, E. Schneidmiller & M. Yurkov Hamburg University: Joern Boedewadt, Axel Winter, Shaukat Khan BESSY-FEL Design Team M. Abo-Bakr, W. Anders, J. Bahrdt, R. Bakker $, K. Bürkmann, G. Bartlock #, G. Bisoffi &, P. Budz, O. Dressler, H. Dürr, V. Dürr, W. Eberhardt, S Eisebitt, J. Feikes, R. Follath, A. Gaupp, A. Goldammer, M. v. Hartrott, Ch. Haberstroh #, I.V. Hertel*, S. Heßler, K. Holldack, E. Jaeschke, D. Janssen %, Th. Kamps, S. Khan, J. Knobloch, D. Krämer, B. Kuske, P. Kuske, A. Kutschbach #, F. Marhauser, A. Meseck, P. Michel %, G. Mishra §, R. Mitzner, R. Müller, M. Neeb, A. Neumann, F. Noack*, K. Ott, W. Peatman, D. Pflückhahn, H. Prange, H. Quack #, T. Quast, M. Scheer, M. Schnürer*, T. Schroeter, W. Sandner*, F. Senf, I. Will*, G. Wüstefeld, J. Teichert %, P. Tzankow*, Y. Xiang +.

3 CLASSE-Seminar Nov A. Meseck Synchrotron Radiation THz Photon energy (eV) Synchrotron radiation Wavelength (m)

4 CLASSE-Seminar Nov A. Meseck Synchrotron Radiation Sources Wiggler / Undulator Narrow beam Polarization Precisely calculable Pulsed beam High Intensity Wide spectral range Peak brillíance Year Free electron laser X-ray tubes Synchrotron radiation sources 1 st generation 2 nd generation 3 rd generation

5 CLASSE-Seminar Nov A. Meseck K  1 ;  w  1/  Brilliance ~ N 2 K  1 ;  w  1/  Brilliance ~ 2N u Wiggler and Undulator ww s Trajectory Oscillation frequency: Undulator parameter Res. Wavelength: Photonenergie keV Dipolmagnet Undulator Wiggler Brillanz Ph./(s mm 2 mrad 2 0.1%BW)

6 CLASSE-Seminar Nov A. Meseck FEL- Interaction Interchange between electron beam and radiation field: NSNS s s s s Vx Resonance condition for FEL:

7 CLASSE-Seminar Nov A. Meseck FEL- Equation of Motion Pendulum: - Frequency:  0 0   Separatrix  

8 CLASSE-Seminar Nov A. Meseck  0 0  Separatrix 0 0   Separatrix  Amplification ( Low Gain ) The amplification of radiation intensity depends on the electron density. For small electron densities the amplification per turn is small. For  > 0 a net intensity amplification is expected. 

9 CLASSE-Seminar Nov A. Meseck Madey -Theorem: The amplification (Gain) is proportional to the negative derivative of the “resonance- curve” of the spontaneous undulator spectrum. Low Gain 0 0   Separatrix 

10 CLASSE-Seminar Nov A. Meseck Low Gain FEL

11 CLASSE-Seminar Nov A. Meseck JLAB ERL-FEL

12 CLASSE-Seminar Nov A. Meseck Mirrors for FELs

13 CLASSE-Seminar Nov A. Meseck High Gain - SASE FEL Extremely high electron densities lead to a permanent amplification of the radiation intensity. The electrons are bundled into packages: Micro-bunching The electrons radiate coherently.

14 CLASSE-Seminar Nov A. Meseck Spectral Properties of the SASE -FELs The statistic behavior of the FEL radiation is caused by the statistic fluctuations in the density distribution of the electrons. Messung am TTF1 Power [GW] Spectrum [a.u.] Zeit [s] Intensität / mittlere Intensität

15 CLASSE-Seminar Nov A. Meseck HGHG SASE Power [GW] Spectrum [a.u.] Advantages of Seeding

16 CLASSE-Seminar Nov A. Meseck Short Laser Pulse (Ti:Sa) brilliant electron beam High Gain Harmonic Generation (HGHG)* Dispersive section   --  -n-n nn Modulator Radiator *Developed by L.-H. Yu et al.,BNL Phys. Rev. A44/8 (1991) 5178

17 CLASSE-Seminar Nov A. Meseck Cascaded HGHG-FEL Laser s Final Amplifier r1 = s /n 1 r2 = s /n 1 /n 2 f = r2 1.Stage 2.Stage

18 CLASSE-Seminar Nov A. Meseck Down-conversion of the seeding wavelength to the desired wavelength. With fresh bunch technique - Classical HGHG a) with final amplifier b) with an extended last radiator Without fresh bunch technique - Modulator cascade - Radiator cascade - Combination of modulator and radiator cascade - Superradiant cascade Cascading towards  < 1nm

19 CLASSE-Seminar Nov A. Meseck Imprinted energy modulation Energy modulation Output power Total energy spread in radiator Linking Bunch, Seed and Undulator Parameters Dispersion chicane modulator and radiator

20 CLASSE-Seminar Nov A. Meseck Linking Bunch, Seed and Undulator Parameters u = 2.5 cm K = 1 E = 2.3 GeV I = 2000 A

21 CLASSE-Seminar Nov A. Meseck The seeded bunch part is no longer suitable for a further seeding process. Use a long bunch and shift interaction region for each stage Fresh Bunch Technique 2 nd Stage Final Amplifier 1 st Stage Electron bunch seed

22 CLASSE-Seminar Nov A. Meseck Signal to Noise Ratio and Seed Power Ensure that the phase correlation and pulse length are conserved! the shot-noise effects are suppressed! * E. Saldin et a., Opt. Comm. 202 (2002) 169 * Limits the total harmonic number High seed power required

23 CLASSE-Seminar Nov A. Meseck Classical High-Gain Harmonic-Generation Cascade using Fresh Bunch Technique and Final Amplifier ELECTRON BEAM Beam energy GeV Peak current 1.8 kA Bunch charge 2.5 nC Emittance (slice) 1.5  mm mrad Repetition rate 1 kHz (later 25) SEEDING RADIATION Photon energy 2.7–5.4 eV Peak power 500 MW Pulse duration < 20 fs Modulator 1 Radiator 1 Laser e- beam Chicane Radiator 2 Chicane FB-Chicane Modulator 2 Final Amplifier FB-Chicane Bessy FEL : LE-Line

24 CLASSE-Seminar Nov A. Meseck Classical High-Gain Harmonic-Generation Cascade using Fresh Bunch Technique ELECTRON BEAM Beam energy: GeV Peak current: 0.5 kA Emittance (slice) :1.5  mm mrad SEEDING RADIATION Photon energy: 1.4 eV? Peak power: 275 MW Pulse duration: < 20 fs Modulator 1 Radiator 1 Laser e- beam Chicane Radiator 2 Chicane FB-Chicane Modulator 2 STARS Radiator 2

25 CLASSE-Seminar Nov A. Meseck Modulator Cascade The bunching achievable at the beginning of the radiator (black) depends on the initial energy spread. The power emitted after one radiator module (red) shows the same dependency. Very small initial energy spread necessary Modulator 1 Laser Electron beam Chicane Radiator 1 Modulator 2 Chicane

26 CLASSE-Seminar Nov A. Meseck Split Modulators Cascade Laser Electron beam Modulator 1Radiator 2 Chicane Modulator 1 Due to the slippage, the reduction of the effective energy spread is much lower for the short pulse (red) than for the CW pulse (black).

27 CLASSE-Seminar Nov A. Meseck Split Modulators Cascade The output power of a split modulator cascade compared with a corresponding regular two stage HGHG cascade. Laser Electron beam Modulator 1Radiator 2 Chicane Modulator 1 Despite reduction too high energy spread Benefits from longer seed pulses

28 CLASSE-Seminar Nov A. Meseck Modulator Cascade – ECHO Scheme Modulator 1 Laser1 Electron beam Chicane Radiator 1 Modulator 2 Chicane Laser2 Modulator 1 + Chicane 1 Modulator 2 + Chicane 2 G. Stupakov FEL 2009

29 CLASSE-Seminar Nov A. Meseck Modulator Cascade – ECHO Scheme Modulator 1 Laser1 Electron beam Chicane Radiator 1 Modulator 2 Chicane Laser2 Modulator 1 + Chicane 1 Modulator 2 + Chicane 2 G. Stupakov FEL 2009

30 CLASSE-Seminar Nov A. Meseck Radiator Cascade Suffers from built up of effective energy spread in first radiator Modulator 1 Laser Electron beam Radiator 1 Radiator 2 Chicane

31 CLASSE-Seminar Nov A. Meseck Modulator and Radiator Cascade * Modulator Cascade: very small initial energy spread necessary Radiator cascade: suffers from built up of effective energy spread in first radiator Combination: combination of problems of modulator and radiator cascade is fatal at least in low energy case Modulator 1 Laser Electron beam Radiator 1 Radiator 2 Chicane Modulator 2 Chicane * DEVELOPMENTS IN CASCADED HGHG-FELs ∗ B. Kuske, A. Meseck, The output of the last radiator of the BESSY LE- FEL(black), the corresponding radiator (blue) and modulator (red) cascades. The low initial energy spread necessary for the modulator cascade causes the lower noise level.

32 CLASSE-Seminar Nov A. Meseck Laser Electron beam Modulator 1Radiator 1Radiator 2 Chicane Superradiant Radiator Cascade Strong (short) seed field Saturation in bunching in first modulator Super radiant pulses in long radiators : inherent fresh bunch Frequency conversion with dispersive chicanes possible but not necessary Super radiance endures frequency conversion Giannessi FEL2005

33 CLASSE-Seminar Nov A. Meseck Laser Electron beam Modulator 1Radiator 1Radiator 2 Chicane Superradiant Radiator Cascade Strong (short) seed field Saturation in bunching in first modulator Super radiant pulses in long radiators : inherent fresh bunch Frequency conversion with dispersive chicanes possible but not necessary Super radiance endures frequency conversion

34 CLASSE-Seminar Nov A. Meseck Superradiant Radiator Cascade The radiation output of the HGHG cascade (black) and the super radiant cascade (red) are depicted. As expected, the spectral quality (left) degrades for the very short super radiant pulse. Very short pulses Poor spectral purity Lower peak power due to disadvantageous ratio between Bunching and effective energy spread Laser Electron beam Modulator 1Radiator 1Radiator 2 Chicane

35 CLASSE-Seminar Nov A. Meseck The ratio between superradiance parameter S = s N w / l b and the slippage parameter k = l c /l b (bonifaccio-definitions) is the key-parameter. If the slippage is too small (=> short wavelength), there is no benefit from the superradiant pulse for harmonic generation. Limit of Superradiant cascades

36 CLASSE-Seminar Nov A. Meseck With fresh bunch technique - Classical HGHG a) with final amplifier b) with an extended last radiator Without fresh bunch technique - Modulator cascade - Radiator cascade - Combination of modulator and radiator cascade - Superradiant cascade Cascading towards  < 1nm noise-amplification => HHG seeds ? Increased energy spread too small slippage (=> short wavelength) DEVELOPMENTS IN CASCADED HGHG-FELs ∗ B. Kuske, A. Meseck,

37 CLASSE-Seminar Nov A. Meseck 40nm 800MeV MeV R 1 Laser Electron beam s=40nm FB-Chicane R 2 s=40nm s=20nm s=10nm R 1 HHG-seed 40nm In RAD1 Ende RAD1 RAD2-helisch 40nm RAD2-helisch 20nm RAD2-helisch 10nm Extension: Classical HHG Seeding

38 CLASSE-Seminar Nov A. Meseck 40nm 800MeV MeV R 1 Laser Electron beam s=40nm FB-Chicane M 2 s=40nm s=8nm R 1 R 2 Chicane R 2 HHG-seed 40nm In RAD1 Ende RAD1 MOD2-helisch 40nm Extension of Classical HHG Seeding II

39 CLASSE-Seminar Nov A. Meseck calibration and OTR screens on 7Match and 3SUND1 ORS Experiment at FLASH* OTR screens on 2SUND2 * PRSTAB 11, , 2008

40 CLASSE-Seminar Nov A. Meseck ORS Experiment at FLASH* * PRSTAB 11, , 2008

41 CLASSE-Seminar Nov A. Meseck FROG Trace, ORS Experiment

42 CLASSE-Seminar Nov A. Meseck ERL driven Seeded FELs?

43 CLASSE-Seminar Nov A. Meseck Cornell-ERL Mode A : X-ray

44 CLASSE-Seminar Nov A. Meseck Cornell-ERL Mode A: Soft X-ray

45 CLASSE-Seminar Nov A. Meseck Mode A: Soft X-ray ; Higher Current Bunch Compression Mode A Goal

46 CLASSE-Seminar Nov A. Meseck Cornell-ERL Mode C: Soft X-ray

47 CLASSE-Seminar Nov A. Meseck Cornell-ERL Mode D: Soft X-ray Space charge dominated beam

48 CLASSE-Seminar Nov A. Meseck Seeding Example Mode D- Seed power Imprinted Energy Modulation HHG-Seed?

49 CLASSE-Seminar Nov A. Meseck Mode D- Seed power and Bunching (funda.) Seed energy (50fs): 500nJ -10  J

50 CLASSE-Seminar Nov A. Meseck Mode D- Energy spread and Bunching (funda.) Seed energy (50fs): 250nJ

51 CLASSE-Seminar Nov A. Meseck Coherent Emission P coh  b 2 x I 2   2 x K 2  -2 Determined by the desired wavelength range,  L. Bunching depends mainly on energy deviation. As high as possible, but take the space charge into account! Bunching at the entrance of the radiator of the second stage of STARS with and without space charge force.

52 CLASSE-Seminar Nov A. Meseck Summary Seeded FELs provide reproducible, stable radiation (in terms of wavelength and Intensity) better control on pulse shape and pulse duration transverse and longitudinal coherence Short wavelength seeds (HHG) with high Intensities are still not state-of-the-art => Several cascading scheme, e.g. HGHG, modulator and/or radiator cascades, are proposed or already under construction Seeding can also be used for beam diagnostics, ORS A seeded FEL can also be driven by an ERL