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Laser beam parameter measurements at PITZ

Laser beam parameter measurements at PITZ. J.Bähr Workshop on Laser Pulse Shaping DESY,Zeuthen, November 30, 2006. Outline. 1. Introduction 2. Photocathode Laser 3. Laser beam-line and diagnostics 5. Outlook 6. Summary. 1. Introduction. PITZ photocathode laser

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Laser beam parameter measurements at PITZ

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  1. Laser beam parameter measurements at PITZ J.Bähr Workshop on Laser Pulse Shaping DESY,Zeuthen, November 30, 2006

  2. Outline 1. Introduction 2. Photocathode Laser 3. Laser beam-line and diagnostics 5. Outlook 6. Summary Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  3. 1. Introduction • PITZ photocathode laser • Essentially sub-system of PITZ/FELs: • Determines essentially reachable transversal emittance • Demands: • Pulse energy: equivalent to > 1nC (O(10 μJ)): • For 0.5%QE and 1nC need 1μJ at cathode and ~10 μJ at laser • Flat-top laser beam transversal profile • Flat-top laser beam longitudinal profile (20 ps FWHM rise/fall time: later 2ps (now 5…6ps)) • Stability • User friendly • Designed and realized by I.Will et al. MBI Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  4. 2. Photocathode laser Time scheme of PITZ/FLASH laser • Similar to FLASH photocathode laser • Differences: realized at PITZ • Fully laser diode pumped • Pulse shaper: longitudinal flat top profile • Wavelength:262 nm Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  5. 2. Photocathode laser Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  6. 2. Photocathode laser Micropulses have flat-top shape: • duration: 15…25 ps (configurable) But: • edges: t = 5…6 ps • too long • fluctuation during the flat-top:s = 3…8%  too large Courtesy I.Will (MBI) Streak camera record of the UV output pulses  R&D Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  7. 3. Laser Beam-line & Diagnostics • Allow remote adjustment of the beam • Include laser beam diagnostics • Goal: • Create flat-top transverse laser profile • Illuminate the Beam Shaping Aperture (BSA) with a laser beam (diameter larger than BSA) • Imaging of BSA onto photocathode • Best focus: => Maximize numberof circular interference fringes • Length of beam-line 27 m Proposed and calculated by I.Will Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  8. 3. Laser beam-line& Diagnostics • Laser beam-line at PITZ: length 27m Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  9. 3. Laser beam-line & Diagnostics • Remotely controlled : • BSA • 2 VirtualCathodes • 6 mirrors • Wedgeplates • Pinhole (not used) Whole beam-line Wedge plates Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  10. 3. Laser beam-line & Diagnostics Diagnostics • Transverse position • Virtual cathode (VC) • Quadrant diode (QD) • Transverse shape • Virtual cathode (VC) • Longitudinal Profile • Streak camera • Later : Optical sampling system (OSS) • Laser pulse energy • Photomultiplier: first relative , later absolute • Manual Joule meter Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  11. 3. Laser beam-line& Diagnostics • Virtual cathodes • Measure: • Laser beam size • Laser beam profile • Laser beam position • Two virtual cathodes for different pulse energy ranges • Camera type: JAI M10RS • UV sensitivity • Progressive scan mode,triggered Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  12. 3. Laser beam-line & Diagnostics • Quadrant diode • Goal: • Measure laser beam position in the cathode plane with temporal resolution pulse to pulse (1 μs) • In preparation: S.Korepanov et al. • Mounted near to VC1, on the same movable stage Hamamatsu S4349 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  13. 3. Laser beam-line & Diagnostics Quadrant diode • Commissioning ongoing • First methodical measurements: • σ = 10 µm of displacement jitter in plane of virtual cathode for 300 shots • Pulse train: 64 pulses Measurement Y.Ivanisenko Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  14. 3. Laser beam-line & Diagnostics • Streak camera • Measure longitudinal laser pulse profile • 2nd branch of the laser beam-line: image of crystal plane onto entrance slit of streak camera • Synchro-scan camera • C5680 (Hamamatsu) • UV sensitive • Resolution 2 ps • Longitudinal profile controlled by pulse shaper • Near future: continuous measurement and subsequent control of pulse shaper (M.Krasilnikov) Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  15. Photomultiplier Problem : dynamic range needed:10**4 Laser pulse energy measurement (relative) in first step HV-power supply integrated UV-sensitive Type: H6780-03 Is commissioned, calibration ongoing Pulse to pulse measurement Pulse energy (absolute) measurement Absolute Device not fixed, mobile Manual use  Usable at different positions Foreseen:Permanent absolute monitoring  see talk M.Haenel (this workshop) 3. Laser beam-line & Diagnostics Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  16. 5. Outlook • Aspheric lenses for improved illumination of Beam Shaping Aperture (BSA): homogeneity, efficiency (2007) • Laser pulse energy monitoring by PM (individual pulse), absolute laser pulse energy pulse-to-pulse with diode calibration  Marc Haenel • Quadrant diode commissioning (ongoing) • Continuous control of pulse shaper based on streak camera pulse profile measurement (Beginning 2007) • Optical sampling system (I.Will et al.) for improved longitudinal pulse profile measurement (Jan.2007) • TV-system on laser table (monitoring and readjustment) • Mixing 2-channel laser system (fall/rise time 2ps),2007 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  17. Laser beam parameters essential for operation and optimization of FLASH and XFEL (minimization of transverse emittance) PITZ is a test bench for photocathode laser development PITZ laser steadily supported and upgraded by MBI (including parts of diagnostics) Laser beam-line essential for transverse laser beam shape control on cathode diagnostics tools as part of laser beam-line: Beam position Shape,profiles (longitudinal/transverse), Pulse en ergy R&D on diagnostics ongoing 6. Summary Acknowledgement: to Ingo Will for providing slides Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  18. End Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  19. 4. Practical experience • Avoid parasitic reflections! • How to get laser on cathode? • Adjust laser beam on photo cathode: • 4 degrees of freedom • 2 conditions: keep beam on inner mirror (use:2 diaphragms or scintillating cathode) Two steps: • Laser off; adjust diaphragms by viewing on illuminated cathode • Aline laser beam trough diaphragms Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  20. completely diode-pumped laser operational at PITZ: - differences to the previously used system - flashlamp-pumped boosters: (old system) preamplifier has 6 passes(compared to three passes in the old system) attenuator for tuning the energy of the UV output pulses safety detector for protection of the wavelength conversion crystals in case of malfunction of the laser diode-pumped boosters (new system): Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  21. Control program of the laser based on the standard MOTIF environment • Control system programmed in C++ following ISO/ANSI standard ISO/IEC 14882-1998 • Standard SUN C++ compiler(SUN Workshop Pro 6.02) • GUI written with Xt library and MOTIF • only C++ and ANSI C • additional libraries: • Athena Plot widget (open source) • Spinbox widget (open source) • No other expensive frameworks used. • Communication with DOOCS:Shared memory (POSIX standard) Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  22. 3. Laser beam-line & Diagnostics • Remotely controlled elements • BSA • Pinhole • 1 switchable mirror • 2 cameras 16 axes: rotation or translation Additional elements on laser diagnostics trolley Electronics elements and electronics: MICOS (H.Henschel) Controls: LAbView (M.Winde) Mechanics (H.Luedecke) • 3(4) mirrors Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  23. 4. Practical experience • Reactions after power cut (only laser) - of course : facility depending • All frequencies available for laser, master oscillator running? • Proper control file of laser loaded • Proper timing relative to rf • Event trigger available • Elements of laser beam line in proper position after zero-position run • Remote control of laser properly working Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  24. 4. Practical experience • How to get photo electrons ? • Adjust laser beam on photo cathode (4 d.o.f. and 2 conditions (inner mirror)) ; (use:2 diaphragms, scintillating cathode) • Obey further (trivial) conditions: rf, timing, laser intensity, cathode) • Choice of proper phase  phase scan  Photo electrons!! Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  25. 4. Laser beam-line: Diagnostics • TV-System on Laser table • Goal: • Measure: • Laser beam position • Laser beam inclination • Transverse laser beam profile • Control laser beam parameter • Help for re-adjustment • Status: in preparation, commissioning: fall 2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  26. 3. Laser beam-line & Diagnostics Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  27. 3. Laser beam-line • Laser beam-line at PITZ: length 27m Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  28. Capabilities of the laser Courtesy I.Will (MBI) Laser generates trains of picosecond UV pulses: • typ. duration of the pulse train: 800 ms • repetition rate within the train: f = 1 MHz • energy of the micropulsesat l = 262 nm (UV): Emicro = 20…30 mJ Micropulses have flat-top shape: • duration: 15…25 ps (configurable) But: • edges: t = 5…6 ps too long • fluctuation during the flat-top:s = 3…8% too large Streak camera record of the UV output pulses Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  29. Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

  30. 2. Photocathode laser Courtesy I.Will (MBI) Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ

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