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Laser system at PITZ

Laser system at PITZ. J.Bähr LCLS Injector Commissioning Workshop SLAC, October 9-11, 2006. Outline. 1. Introduction 2. Photocathode Laser 3. Laser beam-line and diagnostics 4. Practical experience 5. Outlook 6. Summary. 1. Introduction. PITZ photocathode laser

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Laser system at PITZ

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  1. Laser system at PITZ J.Bähr LCLS Injector Commissioning Workshop SLAC, October 9-11, 2006

  2. Outline 1. Introduction 2. Photocathode Laser 3. Laser beam-line and diagnostics 4. Practical experience 5. Outlook 6. Summary ICW Workshop SLAC 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 ICW Workshop SLAC 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 ICW Workshop SLAC J.Bähr, DESY, PITZ

  5. 2. Photocathode laser ICW Workshop SLAC 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 ICW Workshop SLAC 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 ICW Workshop SLAC J.Bähr, DESY, PITZ

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

  9. 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 ICW Workshop SLAC J.Bähr, DESY, PITZ

  10. 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 ICW Workshop SLAC J.Bähr, DESY, PITZ

  11. 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 Usable at different positions Foreseen:Permanent absolute monitoring 3. Laser beam-line & Diagnostics ICW Workshop SLAC J.Bähr, DESY, PITZ

  12. 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 ICW Workshop SLAC J.Bähr, DESY, PITZ

  13. 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 ICW Workshop SLAC J.Bähr, DESY, PITZ

  14. 5. Outlook • Program for keeping laser beam on inner mirror • Aspheric lenses for improved illumination of Beam Shaping Aperture (BSA): homogeneity, efficiency • Laser pulse energy monitoring by PM (individual pulse) and laser power meter • Quadrant diode commissioning • Continuous control of pulse shaper based on streak camera pulse profile measurement • Optical sampling system (I.Will et al.) for improved longitudinal pulse profile measurement • TV-system on laser table (monitoring and readjustment) • Mixing 2-channel laser system (fall/rise time 2ps) ICW Workshop SLAC J.Bähr, DESY, PITZ

  15. 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 Laser beam-line essential for transverse laser beam shape control on cathode diagnostics tools as part of laser beam-line: position, shape, intensity 6. Summary Acknowledgement: to Ingo Will for providing slides ICW Workshop SLAC J.Bähr, DESY, PITZ

  16. End ICW Workshop SLAC J.Bähr, DESY, PITZ

  17. 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): ICW Workshop SLAC J.Bähr, DESY, PITZ

  18. 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) ICW Workshop SLAC J.Bähr, DESY, PITZ

  19. ICW Workshop SLAC J.Bähr, DESY, PITZ

  20. 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 ICW Workshop SLAC J.Bähr, DESY, PITZ

  21. 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 ICW Workshop SLAC J.Bähr, DESY, PITZ

  22. 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!! ICW Workshop SLAC J.Bähr, DESY, PITZ

  23. 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 ICW Workshop SLAC J.Bähr, DESY, PITZ

  24. 3. Laser beam-line & Diagnostics ICW Workshop SLAC J.Bähr, DESY, PITZ

  25. 3. Laser beam-line • Laser beam-line at PITZ: length 27m ICW Workshop SLAC J.Bähr, DESY, PITZ

  26. 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 ICW Workshop SLAC J.Bähr, DESY, PITZ

  27. ICW Workshop SLAC J.Bähr, DESY, PITZ

  28. 2. Photocathode laser Courtesy I.Will (MBI) ICW Workshop SLAC J.Bähr, DESY, PITZ

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