LIGHT SOURCES. Lenny Rivkin. Ecole Polythechnique Federale de Lausanne (EPFL) and Paul Scherrer Institute (PSI), Switzerland

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1 LIGHT SOURCES Lenny Rivkin Ecole Polythechnique Federale de Lausanne (EPFL) and Paul Scherrer Institute (PSI), Switzerland CERN Accelerator School: Introduction to Accelerator Physics September 28, Varna, Bulgaria

2 Wavelength continuously tunable!

3 users world-wide Light Sources, L. Rivkin, EPFL & PSI, Fall semester 2008

4 Materials key to our technologies

5 Materials key to our technologies Herzschrittmacher Li-Batterien Neue Materialen für Energie GPS Navigation Funktionale Materialien Air Bag Beschleunigungssensoren Kosmetika TiO 2 Nanopartikel Mobiltelefon SAW Strukturen Künstliches Hüftgelenk Biokompatible Materialien Gläser and Beschichtungen Optische Materialien UV Filter Digitalkamera CCD Chip Artificial Lens Biocompatible Polymers Fahrradrahmen Kohlenstofffasern Composite Materials GMR Lesekopf Magnetische Vielfachschichten LED Display Photonische Materialien Intelligente Kreditkarte Integrated Circuits Genaue Zeit via Satellit Halbleiterbauelemente Micro-Batterien Helmut Dosch, Max Planck Institut für Metallforschung, Stuttgart

6 The brightness of a light source: Source area, S Angular divergence, Ω Flux, F Brightness = constant x F S x Ω G. Margaritondo

7 Steep rise in brightness XFEL Undulators the second wave SLS SOLEIL (F) DIAMOND (UK) ESRF Wigglers SPring8 APS 10 9 Bending magnets Rotating anode Moore s Law for semiconductors Bertha Roentgen s hand (exposure: 20 min)

8 Protein structure Diffraction pattern Ribosome

9 Photons in biology insight into structures Visualization of Alzheimer s plaques Structure of ribosome and proteins V. Ramakrishnan Th. A. Steitz A. E. Yonath = In collaboration with M Cacquevel, J-C Bensadoun, P. Aebischer, Brain and Mind Institute EPFL, Lausanne, Switzerland 2009 PSI, 21 June 2010

10 Higher brightness: more photons on small sample or through a pinhole of ~ λ: coherence measurements on very small probes (few µm crystals) small divergence: compact mirrors, optics elements minimized aberrations short measurement times high transverse coherence phase contrast imaging

11 The electron beam emittance : Source area, S Angular divergence, Ω The brightness depends on the geometry of the source, i.e., on the electron beam emittance Emittance = S x Ω

12 Ring equilibrium emittance σ 0 σ 0 σ = σ σ MS σ 0 >> σ MS to minimize the blow up due to multiple scattering in the absorber we can focus the beam Equilibrium Emittance ε C E 2 q 3 x0 = θ Flatt J x F min =

13 3 types of storage ring sources: 1. Bending magnets: B ~ N e detector short signal pulse broad hν-band time frequency

14 3 types of storage ring sources: 2. Wigglers: large undulations B ~ N e N w x10 Series of short pulses broad hν-band time frequency

15 3 types of storage ring sources: 3. Undulators: small undulations detector continuously illuminated detector long signal pulse narrow hν-band B ~ N e N 2 u x10 3 hν/ hν N time frequency

16 Anatomy of a light source Linac 100 MeV Storage Ring Booster 2.7 GeV Undulators Beam lines

17 About 60 ring sources world-wide J.Als-Nielsen, Des Mc Morrow

18 Undulators T = ( 1 β ) obs T emit λ light λ u 2 2γ

19 Selection of wavelength in an undulator In an undulator an electron (on a slalom) races an emitted photon N S N(orth) S(outh) A B C period λ u δl= nλ electron photon v β c c at A an electron emits a photon with wavelength λ and flies one period λ u ahead to B with velocity v = βc. There it emits another photon with the same wavelength λ. At this moment the first photon is already at C. If the path difference δl corresponds to n wavelengths, then we have a positive interference between the two photons. This enhances the intensity at this wavelength.

20 Selection of wavelength in an undulator II N S N(orth) S(outh) A B C electron photon period λ u v β c c δl= nλ The path difference δl nλ (1 β ) λ u, 1 β 1 2γ 2 λ = u K λ nγ 2 2 detour through slalom [ mm] B[ T ] K = λu

21 Radiation cone of an undulator Undulator radiates from ist whole length L into a narrow cone. Propagation of the wave front BC is suppressed under an angle θ 0, if the path length AC is just shorter by a half wavelength compared to AB (negative interference). This defines the central cone. L = AB AC = 1 2 L 2 ( 1 cosθ ) Lθ Negative interference for λ θ = 2 L 0 R0 = λ ε 0 = θ0r0 = λ L 2 0 L = λ 2

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23 Undulator radiation λ = mm K-edges λ = λu 2nγ 2 1+ K γ 2 θ 2 λ = 1.5 mm 1 2 ( 1 K ) λ 2 = 2n * + λ u Medium energy rings ESRF, APS

24 In-vacuum undulators / s.c. undulators Gaps down to 3 mm

25 Undulator line width Undulator of infinite length N u = λ λ =0 Finite length undulator radiation pulse has as many periods as the undulator the line width is λ λ 1 N u Due to the electron energy spread λ λ = 2σ E E

26 Third Generation Light Sources in Operation Zhentang Zhao PAC07, Albuquerque, New Mexico, June 25, 2007

27 Top-up injection: key to stability TOP-UP INJECTION ELECTRON INTENSITY TIME POSITION < 1 µm Steady state glow at the SLS Light Sources, L. Rivkin, EPFL & PSI, Varna, Bulgaria, September 2010

28 The electron beam emittance : Source area, S Angular divergence, Ω The brightness depends on the geometry of the source, i.e., on the electron beam emittance Emittance = S x Ω

29 Beam emittance Betatron oscillations Particles in the beam execute betatron oscillations with different amplitudes. Transverse beam distribution Gaussian (electrons) Typical particle: 1 - σ ellipse (in a place where α = β = 0) Area = π ε x σ x x σ x Emittance σ x 2 β Units of ε m rad σ x = ε β σ x = ε /β ε = σ x σ x β = σ x σ x

30 Third Generation Light Sources Emittance (nm.rad) LNLS NewSUBARU TLS Kazakhstan PLS MAX II SAGA ELETRRA Bessy II TSRF ALS SLS Soleil Siberia II Indus II ANKA SESAME CLS SPEAR3 CANDLE ASP ALBA SSRF Diamond NSLS II TPS MAX IV PEP-X ESRF Operational Commissioning Construction Planned PETRA III APS SPring Energy (GeV) Zhentang Zhao PAC07, Albuquerque, New Mexico, June 25, 2007

31 PERFORMANCE OF 3 th GENERATION LIGHT SOURCES BRIGHTNESS: DIFFRACTION LIMIT Medium E 3 GLS ESRF APS Spring-8 PHOTON ENERGY [ev]

32 COHERENT EMISSION BY THE ELECTRONS Intensity N Intensity N 2 INCOHERENT EMISSION COHERENT EMISSION

33 FIRST DEMONSTRATIONS OF COHERENT EMISSION ( ) 180 MeV electrons 30 MeV electrons T. Nakazato et al., Tohoku University, Japan J. Ohkuma et al., Osaka University, Japan

34 MUCH HIGHER BRIGHTNESS CAN BE REACHED WHEN THE ELECTRONS COOPERATE WAVELENGTH INCOHERENT EMISSION COHERENT EMISSION

35 X-Ray Laser Fully coherent source of 1 Å X-rays photons pulses Short pulses: femto- to atto-seconds

36 FEL Principles Z. Huang Electrons slip behind EM wave by λ 1 per undulator period (λ u ) x K/γ λ u λ 1 x-ray z e v x E x > 0 v x E x > Due to sustained interaction, some electrons lose energy, while others gain energy modulation at λ 1 e losing energy slow down, and e gaining energy catch up density modulation at λ 1 (microbunching) Microbunched beam radiates coherently at λ 1, enhancing the process exponential growth of radiation power

37 Microbunching through SASE Process undulator entrance half-way saturation full saturation GENESIS - simulation for TTF parameters Courtesy - Sven Reiche (PSI) Light Sources, L. Rivkin, EPFL & PSI, Varna, Bulgaria, September 2010

38 Linac Coherent Light Source at SLAC X-FEL based on last 1-km of existing 3-km linac Å ( GeV) Proposed by C. Pellegrini in 1992 Existing 1/3 Linac (1 km) (with modifications) Injector (35º) at 2-km point New e Transfer Line (340 m) X-ray Transport Line (200 m) Undulator (130 m) Near Experiment Hall UCLA Far Experiment Hall LLNL Light Sources, L. Rivkin, EPFL & PSI, Varna, Bulgaria, September 2010

39 84 meters of FEL Undulator Installed 25 undulators installed 8 more to go

40 Undulator Gain Length Measurement at 1.5 Å: 3.3 m γε x,y 0.4 µm (slice) I pk 3.0 ka σ E /E 0.01% (slice) (25 of 33 undulators installed)

41 Second day measurements (04/11/09) Ni-foil in front of YAG screen has a K-edge at 1.5 Angstrom σ 0.1% (FEL BW) GeV Energy (%) Light Sources, L. Rivkin, EPFL & PSI, Varna, Bulgaria, September 2010

42 Ultrafast X-ray science If you want to understand function, study structure Francis Crick X-ray Free Electron Lasers extend the ultrafast laser techniques to the X-ray domain Seeing structures evolving with time as phenomena take place FEMTO: Slicing technique at synchrotrons Similar technique to reach < 1 fs with XFELs Light Sources, L. Rivkin, EPFL & PSI, Varna, Bulgaria, September 2010

43 Fast processes and short pulses Laser pump / X-ray probe Centre for Molecular Movies, Niels Bohr Institute, University of Copenhagen M. Nielsen

44 1878: E. Muybridge at Stanford Tracing motion of animals by spark photography E. Muybridge L. Stanford Muybridge and Stanford disagree whether all feet leave the ground at one time during the gallop E. Muybridge, Animals in Motion, ed. by L. S. Brown (Dover Pub. Co., New York 1957).

45 Laser slicing Pioneering ideas and experiments at ALS Facilities at ALS, BESSYII, SLS

46 FELs and ERLs COMPLEMENT the Ring sources X-ray FELs atto Peak Brightness G rings 2G rings ERLs Slicing H.-D. Nuhn, H. Winick 10 ps 100 fs 1fs Pulse duration After H.-D. Nuhn, H. Winick

47 END

48 Transverse coherence High brightness gives coherence The knee of a spider Wave optics methods for X-rays (all chapters in Born & Wolf) Holography phase contrast imaging

49 absorption phase contrast Into the hospital? 17.5 kev, synchrotron Franz Pfeiffer results (C.David, F.Pfeiffer) Coherent X-ray Imaging for Life Science Applications Synchrotron Radiation Basics, Lenny Rivkin, EPFL & PSI, Stellenbosch, South Africa, August 2010