Application of ultrafast laser techniques in accelerators

Application of ultrafast laser techniques in accelerators Yuelin LiAccelerator Systems DivisionArgonne National Laboratoryylli@aps.anl.gov

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

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

Lasers and accelerators at birth Ancient: a cave man’s bow ………………. 1929, Cyclotron, Lawrence 1939, Nobel Prize, Lawrence 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

A map for laser applications in accelerators • Laser beam scattering • Laser beam timing • Laser modulation • Laser beam cooling/heating • Laser modulation Radiation/particle source generation Characterization Beam Characterization monitoring Beam Processing treatment Beam generation • Laser beam scattering • Electroptical sampling • Inverse free-electron laser • Laser/accelerator synchronization • Laser pulse shaping • Plasma wake wave accelerator

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

Laser (001) p y x E p z (110) E beam Probe laser P1 P2 e beam Off line test of Electro-optical sampling (EOS) as electron beam diagnostics d0: crystal residual or bias birefringence

Effect of optical bias Raw data Background Background subtracted • The signal can be linear or nonlinear depends on the relative magnitude of d0andd. • The signal can flip sign artificially!

Nonlinear response at near-zero-optical bias geometryexperiment results Artificial sign flip False field minimum Li et al., Appl. Phys. Lett. 88, 251108 (2006)

One has to know d0 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 Implications

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

Free electron lasers • Grow from noise • Microbunching->amplification • Slippage->coherence buildup • Continuously tunable • X-ray capability

Cylindrical lens BBO crystal Correlation signal onto spectrometer Beam splitter laser pulse APS free electron laser and 6 Hz, 0.5 ps, 50 mJ @ 120-530 nm Milton et al., Science 292, 2037 (2001)

What to analyze • Retrieve the amplitude and phase • Measure the statistic properties of phase, and envelope • Comparison with theory of random signal

SASE FEL output as a sum of random raidators 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).] Which can be rewritten as Where, from central limited theorem, R (normal) and f (uniform) are independent random variables. Introduce sw is the SASE bandwidth

SASE FEL output as a sum of random raidators SASE out put Where, R has normal and and f 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 m>0, maxima; m<0, minima. Krinsky, Li, PRE 73, 066501 (2006).

Sample result of statistical calculation This corresponds to the probability distribution function Spike width x=Dt/<Dt> distribution Phase n=f/sw distribution at spike maxima (+) and minima (-) The constants are a=0.8685, h=9.510, c=0.7925. Krinsky, Li, PRE 73, 066501 (2006).

Statistics of FEL dynamics: Statistics of dynamics of thermal light Spike width f’ at local max Spike Spacing f’ at local min Li et al., PRL 89, 234801 (2002); 91, 243602 (2003). Li et al., APB 80, 31 (2006). Simulation:

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).

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

Small-angle Thomson scatteringX-ray duration determined by laser pulse duration nlaser e- Before interaction During interaction nx-ray 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). t

Performance: spectra and brightness for 6 Hz APS linac Sample spectra Brightness and duration Bunch Energy 650 MeV Beta function 1.5 cm Emittance 10 mm Laser 20-fs, 2-J @ 800 nm

Performance with 6 Hz beam X-ray photon flux (photons s-10.1% bandwidth) Peak spectral brightness Photons s-1 mm-2 mrad-2 per 0.1% BW

For APS storage ring? Too high energy but good for G-ray Table 1 Advanced Photon Source Beam and the laser pulse parameters FIG. 1 (a) A g-ray spectrum peaked at 5 MeV; (b) the total flux as a function of the peak photon energy. An acceptance angle of 1/g is used in the calculation, where g 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)

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 >106/s Li et. al., Appl. Phys. Lett. 88, 021113 (2006), AIP news 789

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

Electrons Laser Gun A photoinjector for high brightness beam • 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 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.

{ 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 tolinear space-chargeforce can be fully compensated • An ellipsoidal beam has a linear space-charge field (Reiser’s book)

{ 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.)

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

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

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

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

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).

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

Beam performance: Comparison of space charge field in free space and in the LCLS injector LCLS Free space Li and Lewellen, Phys. Rev Lett, in press.

Emittance evolution with booster Y. Li and J. Lewellen, PRL 100, 078401(2008)

C D AL SF ZSL PP ODL 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 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.

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.

Results with a Gaussian beam with different aperture size Input beam • 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

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).

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.

Application of ultrafast laser techniques in accelerators