Undulators to Free Electron Lasers David Attwood University of California, Berkeley Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 1 Undulator radiation from a small electron beam radiating into a narrow forward cone is very bright Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 2 Undulator radiation Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 3 Spatially coherent undulator radiation Courtesy of Kris Rosfjord, UCB Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 4 Undulators, FELs and coherence Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 5 Desirable qualities of short pulse FELS • Photon energy (SXR/EUV vs. hard x-rays) • High photon flux (photons/pulse) • Short pulses (asec/fsec) • True phase control (spatial and temporal coherence) • Broad tunability • Polarization control • Repetition rate • Synchronization Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 6 Young’s double slit experiment: spatial coherence and the persistence of fringes Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 7 Young’s double slit experiment: spatial coherence and the persistence of fringes Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 8 Young’s double slit experiment with random emitters: Young did not have a laser Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 9 Young’s double slit experiment with phase coherent emitters (some lasers, or properly seeded FELs) Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 10 The bunching advantage of FELs In an undulator with random, uncorrelated electron positions within the bunch, only the radiated self-fields E add constructively. • Coherence is somewhat limited • Power radiated is proportional to Ne (total # electrons) If the radiated fields, or a seed wave, is strong enough to initiate FEL lasing, the electrons form waves of “microbunches” within which the electron positions are well correlated. Now radiated fields from all these electrons are in phase. The resultant electric field scales with Ne, and intensity with Ne2 • Essentially full spatial coherence • Power radiated is proportional to Ne2, a gain approaching 109. Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 11 FEL Physics Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 12 Equations of motion for the stronger electric field FEL Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 13 Undulators and FELs Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 14 Undulators and FELs Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 15 Undulators and FELs “SASE” FEL – no seed (several separate “waves” of electrons possible with uncorrelated phase.) Less peak power, broader spectrum. Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 16 Seeded FEL Seeded FEL. Initial bunching driven by phase coherent seed laser pulse. Improved pulse structure and spectrum. Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 17 Electron axial positions are affected by interaction with the electromagnetic wave, resulting in microbunching on a wavelength scale Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 18 Relativistic electron interacting with an electromagnetic wave of wavelength λ, as it traverses a periodic magnet (λu) • Deviations from zero-field path • Note the “slip” effect Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 19 Electron energies and subsequent axis crossings are affected by the amplitude and relative phase of the co-propagating field Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 20 FEL Microbunching Courtesy of Sven Reiche, UCLA, now SLS Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 21 Gain and saturation in an FEL Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 22 The coherence properties of Free Electron Lasers Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 23 FEL Lasing Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 24 Stanford’s LCLS Free Electron Laser Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 25 26 LCLS 780 eV (1.6 nm) 300 fsec ¼ nC N = 13 × 113 = 1500 (of 33) Δτcoh = 0.55 fsec (165 nm @ 300 nm/fsec) λ/Δλ = 100 78% energy in a single TEM00 mode ϕ-space = 1.2 diffr. Ltd. 27 Nanostructures fabricated for characterizing beam properties of FELs and for imaging experiments Coherence Measurements FEL coherence characterization using Young’s double pinhole, double slit, triple slits, nonredundant arrays, etc. These structures were made using thick Au where great attention was paid to overall film stress. with LCLS SXR Team Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 URA Holography Two dimensional uniformly redundant array used as the reference for holography experiments at FLASH and ALS. The right hand picture is a SEM of a newly fabricated URA pattern with features down to 20 nm. with Stefano Marchesini ILSW_Attwood_Lec3_March2014.pptx 28 Measuring the SASE spectrum at LCLS Courtesy of D. Zhu, J. Hastings, W. Feng, (SLAC); APL 101, 034103 (July 2012) Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 29 Reduced LCLS spectra, thus longer coherence length, with “self-seeding” J. Amann, et al., Nature Photonics 6, 693 (Oct 2012) Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 30 The Linac Coherent Light Source (LCLS), an X-Ray FEL at Stanford Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 31 Free Electron Lasers Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 32 Probing matter on the scale of nanometers and femtoseconds Science and Technology of Future Light Sources (Argonne, Brookhaven, LBNL and SLAC: Four lab report to DOE/Office of Science, Dec. 2008) Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 33 Coherent x-ray diffractive imaging with the FLASH free-electron laser (FEL) in Hamburg, Germany 25 fs diffraction pattern 1 micron Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 Chapman et al, Nature Phys 2 839 (2006) ILSW_Attwood_Lec3_March2014.pptx 34 (LCLS, lasing April 2009, 1st day; saturated lasing 2009; publ. Sept. 2010) 35 Nature 466, 56 (1 July 2010) LCLS 800 eV to 2 keV 1018 W/cm2 80 fs e– bunch 20-40 fs photons 1s binding energy is 870 eV in neutral Ne Hollow core (no 1s e–s), or Ne+10 36 1.8 keV (0.69 nm) 70 fsec 7 µmD KB spot Photosystem 1 Membrane protein (36) complex nanocrystal in 4 µmD H2O jet @ 30 Hz. Each blown away Reconstruction results similar to a larger crystal at 12.4 keV. 37 Single noncrystalline Meme virus 1.8 keV (0.69 nm) 70 fsec 2D to 32 nm period Need identical particles at molecular level for 3D 38 FEL References • J.M.J. Madey, Stimulated Emission of Bremsstrahlung in a Periodic Magnetic Field, J. Appl. Physics 42, 1906 (1971). • R. Bonifacio, C. Pellegrini and L. Narducci, Collective Instabilities and HighGain Regime in a Free Electron Laser, Optics Commun. 50, 373 (1984). • J.B. Murphy and C. Pellegrini, Introduction to the Physics of Free Electron Lasers, Handbook of Free Electron Lasers (North Holland, 1990). • C. Pellegrini and S. Reiche, The Development of X-Ray Free-Electron Lasers, IEEE J.S.T.Q.E. 10, 1393 (2004). • V. Avazyan et al., Generation of GW Radiation Pulses from a VUV Free-Electron Laser Operating the Femtosecond Regime, Phys. Rev. Lett. 88, 104802 (2002); W. Ackermann et al., Operation of a Free-Electron Laser from the Extreme Ultraviolet to the Water Window, Nature Photonics 1, 336 (2007). • Linac Coherent Light Source (LCLS) Design Study Report, SLAC-R-521 (April 1998); M. Cornacchia, Design Study Group Leader. • P. Emma et al., First Lasing and Operation of an Ångstrom-Wavelength FreeElectron Laser, Nature Photonics 4, 641 (2010). Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 39 Archived internet lectures available at www.youtube.com UC Berkeley www.coe.berkeley.edu/AST/sxr2009 www.coe.berkeley.edu/AST/srms www.youtube.com Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 40 FEL Physics: the “slip condition” Professor David Attwood / UC Berkeley / Iranian Light Source Workshop / March 3-4, 2014 ILSW_Attwood_Lec3_March2014.pptx 41
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