A. Neumann, SRF 2011 Chicago, FRIOA07 T. Quast, Helmholtz-Zentrum Berlin Bild von 3d Ellipsoid Future Light Sources Workshop 2012, JLab Available and Future Laser Pulse Shaping Technology courtesy of T. Raocourtesy of L. Hein (Reality and Future Directions for Spatio-Temporal Laser Pulse Shaping)

T. Quast, Future Light Sources Workshop 2012, JLab 2 Laser Pulse Shaping – why do we need it ? Space Charge.. Space charge force of a Gaussian distribution „laser world is gaussian“ Transversal flattop + Longitudinal flattop „beercan“ Space charge forces are linear for 3d ellipsoid: best solution: 2 nd best solution:

T. Quast, Future Light Sources Workshop 2012, JLab 3 Introduction into Laser Shaping Three „stages“ of Laser Pulse Shaping TransversalLongitudinalSpatio-Temporal (3d) + ≠ „easy“ „advanced“ „very ambitious“ Difficulty level Quality gainStability transversal I(r)3++ Good – if reasonably done Longitudinal I(z)7+ Good - (with feedback control) spatio-temporal I{r(z)}10? Poor – relying on nonlinear effects

T. Quast, Future Light Sources Workshop 2012, JLab 4 Spatial Shaping Has to be done carefully transversal Shaping – every one does it.. Gauss to flattop – the simple way: 1.Transport laser to vincinity of gun 2.Overilluminated iris cuts out only the inner „flat“ part 3.Iris is imaged onto the cathode principle 1.High position Stability (iris located near cathode) 2.Robust and simple setup 3.Spot size and laser power can be varied easily (but not independent) 4.Any pattern can be imaged onto cathode 1.what a waste of laser power ! 2.Problems from laser transmission beamline (spot size / shape stability) are transfomed into intensity fluctuations pro con

T. Quast, Future Light Sources Workshop 2012, JLab 5 Transversal Flattop – Pi Shaper asheric optics – Pi shaper - aspheric refractive (reflective) elements - High transmission (90%) - very sensitive to input laser parameters - tilt, decenter, size (few mrad, 10ths of µm) - TEM00 mode required (difficult with UV) w=w 0 w=0.9w 0 w=1.1w 0 from G.Klemz, I.Will, Proc. FEL06 Use both: „mild“ shaper and pinhole T=70% alternative: deformable mirror and genetic algorithm

T. Quast, Future Light Sources Workshop 2012, JLab 6 Longitudinal shaping – different methods Works well but transmission 10E-2 2. DAZZLER - (Acousto Optic Programmable Dispersive Filter) - only up to 100kHz Rep.rate (this rules out many of the existing bunch patterns) - shaping up to a few ps (restricion from possible crystal length) 1.Direct space to time (with grating and mask)

T. Quast, Future Light Sources Workshop 2012, JLab 7 Longitudinal shaping II Pulse Stacking … (large variety) 3. Spatial light modulator (SLM) Practically only for fs pulses 4. Pulse stacking with polarizer (pol. beam splitters) difficult geometric alignment intensity variations due to imperfect polarizers Courtesy of S. Schreiber, DESY

T. Quast, Future Light Sources Workshop 2012, JLab 8 Longitudinal shaping III Birefringent crystals – reduced complexity with Linear setup from H. Tomizawa, RadPhysChem 80, 10 (2010)

T. Quast, Future Light Sources Workshop 2012, JLab 9 Longitudinal shaping IV 3 stage stacker w. birefringent crystals from: A.K. Sharma et al. PRSTAB 12, (2009) 3x YVO 4 d=(24,12,6mm) T= 62%; 532 nm

T. Quast, Future Light Sources Workshop 2012, JLab 10 Longitudinal shaping V High precision pulse shaper (MBI) Theory for N = 10 crystals: 1024 components aranged in 11 groups Taken from: Will, Klemz, Optics Express 16 (2008),

T. Quast, Future Light Sources Workshop 2012, JLab 11 shaper for high resolution 13 crystal pulse shaper for high resolution FWHM = 25 ps edge ~ 2.2 ps edge ~ 2 ps birefringent shaper, 13 crystals OSS signal (UV) Laser pulse shape measured: temperature controlled birefringent crystal motorized rotation stage Gaussian input pulses Shaped ouput pulses Will, Klemz, Optics Express 16 (2008),

T. Quast, Future Light Sources Workshop 2012, JLab 12 Pulse shaping different possible pulse shapes FWHM ~ 11 ps FWHM ~7 ps FWHM ~ 17 ps FWHM ~ 2 ps FWHM ~ 24 ps FWHM ~ 19 ps Flat-top: Simulated pulse-stacker without feedback FWHM ~ 24 ps Gaussian: Feedback with optical sampling system (OSS): - dynamic range of streak camera not sufficient - scanning of 100 subsequent pulses (~0.2ps res.) - shaping is done after oscillator in IR - sampling for feedback signal in the UV courtesy of I. Will, MBI

T. Quast, Future Light Sources Workshop 2012, JLab 13 Self evolving Self evolving beam - space charge force start with a parabolic (or half sphere) Laser intensity profile automatic evolution into a uniform ellipsoidal (3D) beam O. J. Luiten et al., Phys. Rev. Lett. 93, (2004) pro: con: - Easy - no longitudinal laser shaping - only a short (100fs) pulse (clipped gaussian) needed - cannot put high charge in it - short pulse may damage cathode - only fast response photocathode material => metal - requires high accelerating gradient

T. Quast, Future Light Sources Workshop 2012, JLab 14 3d pulse shaping Use chromatic aberration of a dispersive lens Refractive index n is a function of frequency (dispersion) Focal length of focussing lens changes with frequency Parabolic frequency change by giving the pulse a cubic phase Courtesy of Yuelin Li DAZZLER spatial shaper ZnSe lens achromatic lens camera

T. Quast, Future Light Sources Workshop 2012, JLab 15 3d pulse shaping A first proof of principle experiment From Y. Li et al. PRSTAB 12, (2009) In principle it is working -quality suffers from AOPDF limitations - No pinholes in transport ! (changing size) - no dispersion in transport ! - only IR so far (conversion ??)

T. Quast, Future Light Sources Workshop 2012, JLab 16 3d pulse shaping (alternative) Stacking a 3d-ellipsoid… Alignment ? Coherence and diffraction ? Slice number limited con pro No dependance on nonlinear effects Not been demonstrated yet Z.He et al. Proc of PAC2011, TUP200

T. Quast, Future Light Sources Workshop 2012, JLab 17 …back to Reality… Survey on longitudinal shaping Information provided by SimulationsConclusionRealityExperim ent Observation JLabShukui Zhnag, Pavel Evtuschenko Gaussian 3  Better for longitudinal emittance GaussianyesRegular operation, optimal longitudinal emittance for FEL Gaussian with new laser, pulses shorter than old yesReduced gun voltage, new injector settings => reduced longitudinal brightness Superposition of 2 n G. tails 3 . min. ripple center Better for transverse emittance Pulses stretched in 3 birefingent crystals yesStretcher almost never stable; changes in pulse shape made optimization hard; diff. injector setup necessary; after optimization same long. brightness as before Laser modified for longer Gaussian bunches Real longitudinal profiles streak camera pictures approx. by computer code Necessary for agreement between simulations and measurement

T. Quast, Future Light Sources Workshop 2012, JLab 18 …reality II… Survey (cont.) AliceYuri Saveliev, Boris Militsyn Alive studies Paper in Boris ’ only gun beam line Pulse stacker (4x7ps) 28ps FWHM Near future 7ps Gauss  pulse stacker incl. recirculato r Potential benefits wiped out by non- flatness SPARCMassimo Ferrario Flat top pulsesyesBenefits in transverse emittance for charges above 300pC At beginning, transverse nonlinearities reduced & frozen Blow out regimeprofitable for long. phase space for compression Laser combGaining importance THz sources FEL plasma acc. HZBThorsten Kamps, Bettina Kuske 7 ps rms Gaussian  ps flat top Longitudinal: current distribution similar, Energy spread larger in FT Transverse: low charge slices over-focussed Information provided by SimulationsConclusionRealityExperime nt Observation

T. Quast, Future Light Sources Workshop 2012, JLab 19 pulse shaping Summary transversal pulse shaping has to be done carefully with advanced pulse shaping the beam transport becomes an issue (dont mess it up..) advanced and controlled pulse stacking setup for flat top laser pulses work nicely first steps into 3d ellipsoidal shaping are done – further exploration needed  Overall performance of a gun largely depends on careful technical implementation of the Ph. Cath Laser  Stable laser parameters improve the overall performance  Put more emphasis on laser diagnostic and feedback  More complicated shaping schemes, utilizing nonlinear effects causes unwanted coupling of parameters oLess degrees of freedom oPotential source of instability  Is it worth it ? Remarks

T. Quast, Future Light Sources Workshop 2012, JLab 20 Z-polarization gun - laser induced shottky effect z-polarization (interesting concept) „If the Schottky-effect-induced Z-field is large enough, we expect that electrons will make oscillations with the Z- field frequency on the outermost surface of the metal cathode and will be extracted with the external electric field of the RF cavity“ H. Tomizawa, Proc FEL2010 workfunction is lowered of the intense laser field -Requires very moderate laser parameters: 2.6µJ, 100fs, ~800nm -Focussing down to 20µm results in 21 pC