Soft X-ray light sources Light Sources Ulrike Frühling Bad Honnef 2014

Soft X-ray light sources Wave length range VUV - Soft X-Ray 200nm - 0.1nm 6 eV – 1.2 keV

Soft X-ray light sources Wave length range Advantages of VUV – Soft X-ray radiation selective single photon ionization/excitation weak fields  perturbation of molecular orbitals avoided access to deeply bound electron shells high photo-absorption cross section high temporal resolution

Soft X-ray light sources Relevant time scales

Soft X-ray light sources Relevant time scales Pulse duration needs to be short compared to the studied dynamics. long pulse  blured short pulse  sharp

Soft X-ray light sources Variable delay Probe pulse Pump pulse tt Sample Detector Pump Probe experiment M. Drescher Z. Phys. Chem. 218, (2004). We need two short, well synchronized light pulses

Soft X-ray light sources Brilliance Brilliance: Photons / (sec·mrad 2 ·mm 2 ·0.1%bw) Peak brightness: within a pulse Often used to compare light sources, but need to consider the requirements of specific experiments. Can take data over many pulses?  average brightness Nonlinear experiments, or experiments where the target is destroyed by each pulse  “peak” brilliance HHG

Soft X-ray light sources Synchrotron radiaton ESRF

Soft X-ray light sources Synchrotron radiaton Petra III Undulator -Sinusoidal electron trajectory in the undulator -Emission of Radiation at every bend -Coherent superposition of light pulses emitted at consecutive bends leads to highly brilliant beam -Wavelength tunable by changing the undulator gap

Soft X-ray light sources Synchrotron radiaton Synchrotron radiaton sources Photonenergy: VUV to hard X-Rays (few eV to 100 keV) High repetition rate (MHz) Tuneable wavelenght, good spectral resolution (with monochromator) Pulseduration: tens to >100 ps

Soft X-ray light sources Superimpose ps electron bunch with fs laser pulse to modulate the electron energy. Use only the modulated electrons for synchrotron radiation fs Synchrotron Pulses - Slicing S. Kahn et al., PRL 97, (2006).

Soft X-ray light sources fs Synchrotron Pulses - Slicing S. Kahn et al., PRL 97, (2006).

Soft X-ray light sources fs Synchrotron Pulses - Slicing Intensity is reduced by Pulse duration: 100 fs Photon energy: 300 – 1400 eV Sources available at Bessy, PSI S. Kahn et al., PRL 97, (2006). Energy modulation

Soft X-ray light sources Free-electron laser >10 6 higher irradiance than synchrotrons XUV: E max ~ Wcm -2 (FLASH) X-ray: E max ~ Wcm -2 (LCLS)  Sources for multi-photon processes in the XUV/X-ray range fs pulse duration  Time resolved experiments Repetition rate: few Hz to kHz

Soft X-ray light sources FEL Experiments A.A Sorokin et al., PRL 99, (2007). = 13.3 nm (93 eV) focus: 2.6  m (f =200 mm) E = – W cm -2 Xe 21+  57 photons Photoeffect at ultra high intensities

Soft X-ray light sources Proposed facilities and facilities under construction not listed DESY FLASH > 7 nm SLAC LCLS > 0.12 nm SPring-8 SCSS-TA > 40 nm SACLA > 0.1 nm Elettra FERMI > 40 nm VUV/Soft X-ray FELs

Soft X-ray light sources Free-electron laser Linear accelerator  highly compressed, well defined electron bunch Long undulator several 10 m)

Soft X-ray light sources Free-electron laser SASE-self amplified spontaneous emission Spontaneous undulator emission

Soft X-ray light sources Free-electron laser SASE-self amplified spontaneous emission Energy modulation of electrons in the copropagating light field

Soft X-ray light sources Free-electron laser SASE-self amplified spontaneous emission Energy modulation leads to increasing density modulation of the electron bunch (microbunching) Bunch period:   coherent emission  P  N e 2 

Soft X-ray light sources SASE FEL properties SASE-self amplified spontaneous emission No oscillator  fluctuation of spectrum, pulse shape, pulse-energy Solution: single shot measurement of all beam parameters + sorting of experimental data

Soft X-ray light sources SASE FEL properties SASE-self amplified spontaneous emission No oscillator  fluctuation of spectrum, pulse shape, pulse-energy Solution: single shot measurement of all beam parameters + sorting of experimental data FLASH single shot spectra Average FWHM-width: 1,7% FLASH Pulse energy

Soft X-ray light sources SASE FEL properties SASE-self amplified spontaneous emission No oscillator  fluctuation of spectrum, pulse shape, pulse-energy Solution: single shot measurement of all beam parameters + sorting of experimental data FLASH pulse duration Average FWHM-duration: 35 fs FLASH Pulse shape (simulated)  = 13.7 nm

Soft X-ray light sources 200 µm Optical laser: 400 nm, 130 fs FLASH: 28 nm, 25 fs CCD GaAs Single shot time delay measurement Intense XUV radiation changes reflectivity for optical laser Synchronization

Soft X-ray light sources t (ps) Nominal delay stage setting (ps) Delayscan over temporal window of 2.3 ps Alternative methods: Electro-optical sampling Sidebands T. Maltezopoulos et al., New Journ. Phys. 10, (2008).

Soft X-ray light sources Jitter-compensated ion signal Red curve – expected results with nominal XUV and laser parameters sorted with timing experiment delay scan

Soft X-ray light sources FEL Seeding schemes e.g. High-Harmonic Generation (HHG) Wavelength record: 38 nm (FLASH) Low seed power Difficult Synchronization Direct seeded FEL (amplifier mode) High-gain harmonic generation (HGHG)HGHG-cascade Wavelength record: 20 nm (FERMI) Wavelength record: 4 nm (FERMI)

Soft X-ray light sources FEL Seeding schemes Self-Seeding SASE Wavelength record: 0.12 nm (LCLS) -no external seed difficulties -no direct control over pulse length, chirp, synchronization, etc… Most seeding projects are still experimental User operation only at Fermi (20-65 nm)

Soft X-ray light sources High-harmonic generation atomic gas target Spherical mirror fs nir-laser

Soft X-ray light sources High-harmonic generation “Three-step model” Kheldysh et.al. Gas atom “Femtosecond x-ray science”, T. Pfeifer, C. Spielmann and G. Gerber, Rep. Prog. Phys. 69 (2006) 443–505

Soft X-ray light sources High-harmonic generation HHG-Spectrum E cutoff = I p +3U p U p = e 2 E 0 2 /(4m e  2 )~ I  Pulse-duration is determined by the driving laser (fs to as). Pulse energy:  J (VUV) nJ (<100 nm) Perfect XUV/laser synchronization Laser like XUV pulses

Soft X-ray light sources HHG setup Laser: 800 nm, 25 fs, 2 mJ/pulse XUV: 13.5 nm (higher harmonics generation) B. Schütte PhD-Thesis (2012)

Soft X-ray light sources Generation of as-pulses Carrier envelope phase (CEP) A. Baltuska et al., Nature 421, 611 (2003).

Soft X-ray light sources Light field driven streak-camera R. Kienberger et al., Nature 427, 817 (2004). resolution: < 100 as I XUV (t)  I e (p)  I e (E) XUV pulse Atoms Electrons Electron energy detector IR light field

Soft X-ray light sources Light field driven streak-camera R. Kienberger et al., Nature 427, 817 (2004). time el. field strength / vector potential A electron momentum change electron-momentum distribution I(E kin )  p(t) = e A(t) XUV wave packet |  (t)| 2 XUV pulse Atoms Electrons Electron energy detector IR light field

Soft X-ray light sources Streaking with visible light E. Goulielmakis et al., Science 305, 1267 (2004). Kienberger et al., Nature 427, 817 – 821 (2004).

Soft X-ray light sources Sources for ultra short XUV pulses Pulse duration (fs)Photon energy (eV)Light flux ( photons/s ) High harmonics0.2 – – Laser plasma> – Synchrotron> – Synchrotron + slicing 100 – – Free-electron laser –

Soft X-ray light sources Thank you