1. Application of ultrafast laser techniques in accelerators Yuelin Li Accelerator Systems Division Argonne National Laboratory ylli@aps.anl.gov

2. Sector 7 seminar, July 8, 2008 2 Acknowledgements Colleagues Steve Milton, Kwang-Je Kim, Kathy Harkay, John Lewellen, Vadim Sajaev, Yong-chul Chae, Yin-e Sun (Argonne National Laboratory) Guest scientists: Baifei Shen (Shanghai Institute of Optics and Fine Mechanics) Karoly Nemeth, John Bailey

3. Sector 7 seminar, July 8, 2008 3 Content Laser and accelerator history Laser applications in accelerators Review of recent laser/accelerators work at the APS –Electro-optical sampling –Free-electron laser characterization –Ultrashort, bright x-ray, Gamma-ray, and positron pulses –Coherent THz generation –Laser plasma accelerator simulation –3-D Laser pulse shaping for photoinjectors Summary

4. Sector 7 seminar, July 8, 2008 4 Lasers and accelerators at birth Ancient: Let there be light ………………….. 1917, theory of stimulated radiation by Einstein 1960, flash-lamp pumped ruby, Dr. Mainman 1964, Nobel Prize, Towne, Basov, and Prokhorov Ancient: a cave man’s bow ………………. 1929, Cyclotron, Lawrence 1939, Nobel Prize, Lawrence

5. Sector 7 seminar, July 8, 2008 5 A map for laser applications in accelerators Beam generation Beam Characterization monitoring Beam Processing treatment Radiation/particle source generation Characterization Laser/accelerator synchronization Laser pulse shaping Plasma wake wave accelerator Laser beam cooling/heating Laser modulation Laser beam scattering Electroptical sampling Inverse free-electron laser Laser beam scattering Laser beam timing Laser modulation

6. Sector 7 seminar, July 8, 2008 6 Content Laser and accelerator history Laser applications in accelerators Review of recent laser/accelerators work at the APS –Electro-optical sampling –Free-electron laser characterization –Ultrashort, bright x-ray, Gamma-ray, and positron pulses –Coherent THz generation –Laser plasma accelerator simulation –3-D Laser pulse shaping for photoinjectors Summary

7. Sector 7 seminar, July 8, 2008 7 Electro-optical sampling and application To measure the longitudinal beam profile –Yan et al., PRL 85, 3404 (2000); –Berden et al., PRL 93, 114802 (2004), 300 fs To measure beam position and transverse beam profile –R&D at NIU and Spting8 As a timing tag –SPPS : Cavalieri et al., PRL 94, 114801 (2005), 300 fs To measure THz radiation –TDS, etc

8. Sector 7 seminar, July 8, 2008 8  0 : crystal residual or bias birefringence (00 1) z (110) x y p p E E beam Laser P1 P2 e beam Probe laser Off line test of Electro-optical sampling (EOS) as electron beam diagnostics

9. Sector 7 seminar, July 8, 2008 9 Effect of optical bias The signal can be linear or nonlinear depends on the relative magnitude of  0 and  The signal can flip sign artificially! Background Raw data Background subtracted

10. Sector 7 seminar, July 8, 2008 10 Nonlinear response at near-zero-optical bias geometry experiment results False field minimum Artificial sign flip Li et al., Appl. Phys. Lett. 88, 251108 (2006)

11. Sector 7 seminar, July 8, 2008 11 Implications One has to know  0 to retrieve –Timing: when it starts? –Amplitude: what is the maximum? Or work at larger optical bias –Combating with big background with smaller signal It has significant implication for using EOS as timing and profile measurement techniques

12. Sector 7 seminar, July 8, 2008 12 Content Laser and accelerator history Laser applications in accelerators Review of recent laser/accelerators work at the APS –Electro-optical sampling –Femto statistic optics using a free electron laser –Ultrashort, bright x-ray, Gamma-ray, and positron pulses –Coherent THz generation –Laser plasma accelerator simulation –3-D Laser pulse shaping for photoinjectors Summary

13. Sector 7 seminar, July 8, 2008 13 Free electron lasers Grow from noise Microbunching- >amplification Slippage->coherence buildup Continuously tunable X-ray capability

14. Sector 7 seminar, July 8, 2008 14 APS free electron laser and 6 Hz, 0.5 ps, 50  J @ 120-530 nm Milton et al., Science 292, 2037 (2001) laser pulse Beam splitter BBO crystal Cylindrical lens Correlation signal onto spectrometer

15. Sector 7 seminar, July 8, 2008 15 What to analyze Retrieve the amplitude and phase Measure the statistic properties of phase, and envelope Comparison with theory of random signal

16. Sector 7 seminar, July 8, 2008 16 The field of a SASE FEL (by solving Green’s function) is [S. Krinsky and Z. Huang, Phys. Rev. ST Accel. Beams 6, 050702 (2003).] SASE FEL output as a sum of random raidators Which can be rewritten as Where, from central limited theorem, R (normal) and  (uniform) are independent random variables. Introduce   is the SASE bandwidth

17. Sector 7 seminar, July 8, 2008 17 SASE FEL output as a sum of random raidators SASE out put Where, R has normal and and  has uniform random distributions. Introducing, Under these conditions, it is has been calculated (S. O. Rice, Bell Syst. Tech. J. 24, 46 1945. See Section 3.8.) that at intensity extremes, the distribution function is  >0, maxima;  <0, minima. Krinsky, Li, PRE 73, 066501 (2006).

18. Sector 7 seminar, July 8, 2008 18 Sample result of statistical calculation This corresponds to the probability distribution function Spike width  distribution Phase =  /   distribution at spike maxima (+) and minima (-) The constants are a=0.8685,  =9.510,  =0.7925. Krinsky, Li, PRE 73, 066501 (2006).

19. Sector 7 seminar, July 8, 2008 19 Statistics of FEL dynamics: Statistics of dynamics of thermal light Li et al., PRL 89, 234801 (2002); 91, 243602 (2003). Li et al., APB 80, 31 (2006). Spike width  ’ at local max Spike Spacing  ’ at local min Simulation:

20. Sector 7 seminar, July 8, 2008 20 Implications for XFEL: Number of coherent spikes First time resolved statistics Pulse duration estimate for XFEL –No methods is envisaged to directly measure the XFEL pulse duraion –Spectral measurement is straight forward –With the correlation, one can infer the XFEL pulse duration from the number and width of the spectral spikes –Idea is being used by DESY Li et al., APB 80, 31 (2006).

21. Sector 7 seminar, July 8, 2008 21 Content Laser and accelerator history Laser applications in accelerators Review of recent laser/accelerators work at the APS –Electro-optical sampling –Free-electron laser characterization –Ultrashort, bright x-ray, Gamma-ray, and positron pulses –Coherent THz generation –Laser plasma accelerator simulation –3-D Laser pulse shaping for photoinjectors Summary

22. Sector 7 seminar, July 8, 2008 22 Thomson scattering for ultrashort X-ray pulses Thomson scattering –Double Doppler frequency shift Pulse durations, with a ultrafast laser –Head on: bunch length –Bunch cross section

23. Sector 7 seminar, July 8, 2008 23 Small-angle Thomson scattering X-ray duration determined by laser pulse duration e-e- laser x-ray t Before interaction During interaction After interaction Short pulse X-ray generation Y. Li, Z. Huang, M. Borland, and S. Milton Phys Rev. ST-AB 5, 044701 (2002). Khan et al., Proc. PAC 97, 1810 (1997).

24. Sector 7 seminar, July 8, 2008 24 Performance: spectra and brightness for 6 Hz APS linac Bunch Energy650 MeV Beta function1.5 cm Emittance10  m Laser20-fs, 2-J @ 800 nm Sample spectraBrightness and duration

25. Sector 7 seminar, July 8, 2008 25 Performance with 6 Hz beam X-ray photon flux (photons s -1 0.1% bandwidth) Peak spectral brightness Photons s -1 mm -2 mrad -2 per 0.1% BW

26. Sector 7 seminar, July 8, 2008 26 For APS storage ring? Too high energy but good for G-ray Table 1 Advanced Photon Source Beam and the laser pulse parameters BeamLaser Particles per pulse10 11 (15 nC)2×10 16 (5 mJ) Electron, photon energy7 GeV1.55 eV Energy spread (rms)0.1%0.5% Pulse duration45 ps0.1-1 ps Repetition rate6.528 MHz4 kHz RMS beam size 92  m×26  m 26  m×26  m FIG. 1 (a) A  -ray spectrum peaked at 5 MeV; (b) the total flux as a function of the peak photon energy. An acceptance angle of 1/  is used in the calculation, where  is the relativistic factor of the beam. In (b), the peak photon energy is tuned by changing the interaction angle between the laser and the electron beam. Here a laser repetition rate of 4 kHz and an optical cavity with a quality factor of 1000 at 6.52 MHz is considered. Li et. al., Appl. Phys. Lett. 88, 021113 (2006)

27. Sector 7 seminar, July 8, 2008 27 Generating of ultrafast positron beams Strike a target/sample to generate pairs Detexcting the annihilation gamma to obtain information on defect and structure change Good for in-situ bulk material structure probe with high temporal resolution Li et. al., Appl. Phys. Lett. 88, 021113 (2006), AIP news 789 >10 6 /s

28. Sector 7 seminar, July 8, 2008 28 Content Laser and accelerator history Laser applications in accelerators Review of recent laser/accelerators work at the APS –Electro-optical sampling –Free-electron laser characterization –Ultrashort, bright x-ray, Gamma-ray, and positron pulses –Coherent THz generation –Laser plasma accelerator simulation –3-D Laser pulse shaping for photoinjectors Summary

29. Sector 7 seminar, July 8, 2008 29 3D laser pulse shaping outline Beam brightness –Need for high brightness beams –Definition brightness and emittance –Constraints Cathode emittance: thermal and beam size Emittance growth Way to increase brightness –Using rf photocathode injector Lower temperature to reduce thermal emittance Short pulse duration to increase peak brightness Pulse shaping to compensate for emittance growth –Other ways Emittance exchange Beam cooling etc

30. Sector 7 seminar, July 8, 2008 30 A photoinjector for high brightness beam D. Dowell et al., “The status of normal conducting RF (NCRF) guns, a summary of the ERL2005 workshop,” NIMA 557, 61 (2005). C. Sinclair, ibid, “DC photoemission electron guns as ERL sources,” p. 69. D. Janssen et al., ibid, “Technology challenges for SRF guns as ERL sources in view of Rossendorf work,” p. 80. Laser Electrons Gun Why high brightness? –Synchrotron/ERL light sources: more photons and better coherence –Free-electron lasers: shorter undulators lines and beam energy, 50% reduction in emittance saves 15% of total cost Solution step one: potocathode rf gun: The electron beam has less thermal energy High accelerating field at cathode –DC gun: 5-8 MV/m –RF gun: 40-100 MV/m The electron beam carries over the laser beam 3-D shape

31. Sector 7 seminar, July 8, 2008 31 Brightness, emittance, emittance growth, emittance compensation, and an ellipsoidal beam Brightness Emittance Space-charge force and emittance growth Emittance compensation With proper arrangement of the solenoid, emittance growth due to linear space-charge force can be fully compensated An ellipsoidal beam has a linear space-charge field (Reiser’s book) {

32. Sector 7 seminar, July 8, 2008 32 An uniform ellipsoidal beam Uniform electron density distribution in a ellipsoid Has linear space charge force (M. Reiser, Theory and Design of Charged Particle Beams, Wiley, New York.) {

33. Sector 7 seminar, July 8, 2008 33 Realization of an Ellipsoid: Luiten Scheme Pro –Easy: Need a short pulse (100 fs) with initial parabolic transverse distribution, no longi shaping needed –Potentially high peak current at the gun exit Con –Cannot put too many charges: image charge will distort the beam –Pancake geometry thus larger transverse size: larger cathode emittance to start with –Short, intense pulse may damage transport optics and cathode –Fast response precludes many cathode material, stuck with metal How about an ellipsoidal pulse? J.Luiten, “How to realize uniform 3-dimensional ellipsoidal electron bunches”, Phys.Rev.Letters Aug04

34. Sector 7 seminar, July 8, 2008 34 3D laser pulse shaping to generate an ellipsoidal beam Difficulties –Simultaneous evolving longitudinal and transverse profiles –Homogeneous in 3-D Existing methods: pulse stacking, not really Our method: real 3-D pulse shaping by spatiotemporal coupling via dispersion

35. Sector 7 seminar, July 8, 2008 35 Ellipsoidal pulse: Gaussian analysis and simulation Y. Li and J. Lewellen, PRL 100, 078401(2008) With ellipsoidal boundaries, Nees a top-hat transverse profile t t Beam size w

36. Sector 7 seminar, July 8, 2008 36 Numerical calculation: Fourier optics Full wave optics (Fresnel diffraction) adapted from Kempe et al. (JOSA B 9, 1158 (1992)) Group velocity dispersion and group velocity delay effect considered up to the second order

37. Sector 7 seminar, July 8, 2008 37 The 3D laser pulse at the focal plane of a lens f=150 mm, a=50 mm, 249 nm, 6 ps FW Li and Lewellen, Phys. Rev Lett, 100, 078401 (2008).

38. Sector 7 seminar, July 8, 2008 38 Simulation for the Linear Coherent Light Source (LCLS) M. Ferrario et. al., “NEW DESIGN STUDY AND RELATED EXPERIMENTAL PROGRAM FOR THE LCLS RF PHOTOINJECTOR,” Pac 2000, p 1644 Q>=1 nC  <=1 mm mrar (Credit: Dowell, SLAC)

39. Sector 7 seminar, July 8, 2008 39 Beam performance: Comparison of space charge field in free space and in the LCLS injector Free space LCLS Li and Lewellen, Phys. Rev Lett, in press.

40. Sector 7 seminar, July 8, 2008 40 Emittance evolution with booster Y. Li and J. Lewellen, PRL 100, 078401(2008)

41. Sector 7 seminar, July 8, 2008 41 A proof of principle experiment To show the physics To show technical feasibility Experimental setup –800 nm laser, 1 kHz, 10 nJ perpulse, 40 nm bandwidth –ZnSe lens as the focal lens –DAZZLER as the phase modulator –Achromatic lens for transport C AL ZSL SF PP D ODL Figure 1. Schematic of the experiment. Keys: PP: pulse picker; D: AOPDF; SF: achromatic spatial filter; ZSL: ZnSe lens; AL: achromatic image relay lens; ODL: optical delay line; C: camera.

42. Sector 7 seminar, July 8, 2008 42 Acousto-optic Programmable Dispersive filter It launches an acoustic wave along the beam in a birefringent crystal. The input polarization is diffracted to the other by the sound wave. The frequency that has its polarization rotated depends on the acoustic-wave frequency. Its relative delay at the crystal exit depends on the relative group velocities of the two polarizations.

43. Sector 7 seminar, July 8, 2008 43 Results with a Gaussian beam with different aperture size Demonstrated validity of the theory and method Work for the future –Need large, flat topped beam: more laser energy –Need even more energy for frequency conversion –Adaptive control Input beam

44. Sector 7 seminar, July 8, 2008 44 Publications on laser related work 3D laser pulse shaping and propagation for high brightness beam generation –Y. Li and J. Lewellen, Phys. Rev. Lett. 100, 078401 (2008). –Y. Li and S. Chemerisov, Opt. Lett., in press. –Y. Li and Crowell, Opt. Lett. 32, 93 (2007). Pulse train generation for high power THz radiation –Y. Li and K. Kim, Appl. Phys. Lett. 92, 014101 (2008); –Li, Sun and Kim, PRSTAB, in press Laser beam interaction for ultrfast X-ray and Gamma ray generation –Y. Li, Guo, Liu, and Harkay, Appl. Phys. Lett. 89, 021113 (2006); –Y. Li, Huang, and Borland, Phys Rev ST AB 5, 044701 (2002). EO application for accelerator –Y. Li, Appl. Phys. Lett. 88, 251108 (2006). Laser plasma accelerator simulations –K. Nemeth, et al, Phys. Rev. Lett. 100, 095002 (2008); –B. Shen, Li, Yu, and J. Cary, Phys. Rev. E 76, 055402 (R) (2007); –B. Shen, et al., Phys. Plasmas 14, 053115 (2007); FEL diagnostics and Femto statistical optics –S. Krinsky, Y. Li, PRE 73, 066501 (2006); –Y. Li et al., Appl.Phys B 80, 31 (2005); –Y. Li et al, Phys Rev Lett. 91, 243602 (2003); –Y. Li et al., Phys Rev Lett 89, 234801 (2002); 90, 199903 (2003).

45. Sector 7 seminar, July 8, 2008 45 Summary The marriage of accelerators and lasers is unavoidable and is a rich field of applications, sciences, and challenge, in both enhancing capability of controlling and measuring the beams in a conventional accelerator, and in generating novel light and particle sources.