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

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 2 Outline 1. Introduction 2. Photocathode Laser 3. Laser beam-line and diagnostics 4. Practical experience 5. Outlook 6. Summary

9-11/10/2006 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

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 4 2. Photocathode laser Similar to FLASH photocathode laser  Differences: realized at PITZ Fully laser diode pumped Pulse shaper:  longitudinal flat top profile Wavelength: 262 nm Time scheme of PITZ/FLASH laser

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 5 2. Photocathode laser

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 6 2. Photocathode laser Micropulses have flat-top shape:  duration: 15…25 ps (configurable) But:  edges:  = 5…6 ps  too long  fluctuation during the flat-top:  = 3…8%  too large Streak camera record of the UV output pulses Courtesy I.Will (MBI)  R&D

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 7 3. Laser Beam-line & 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 number of circular interference fringes Proposed and calculated by I.Will  Allow remote adjustment of the beam  Include laser beam diagnostics Length of beam-line 27 m

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 8 3. Laser beam-line & Diagnostics Whole beam-line Wedge plates Remotely controlled : BSA 2 VirtualCathodes 6 mirrors Wedgeplates Pinhole (not used)

9-11/10/2006 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

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 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

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ Laser beam-line & Diagnostics Photomultiplier  Problem : dynamic range needed:10**4  Laser pulse energy measurement (relative) in first step  HV-power supply integrated  UV-sensitive  Type: H  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

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 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

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ Practical experience 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: 1. Laser off; adjust diaphragms by viewing on illuminated cathode 2. Aline laser beam trough diaphragms Avoid parasitic reflections!

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 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)

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ Summary 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 Acknowledgement: to Ingo Will for providing slides

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 16 End

9-11/10/2006 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):

9-11/10/2006 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 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)

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 19

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 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

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 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

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 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!!

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 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

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ Laser beam-line & Diagnostics

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ Laser beam-line Laser beam-line at PITZ: length 27m

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 26 Capabilities of the laser Laser generates trains of picosecond UV pulses:  typ. duration of the pulse train: 800  s  repetition rate within the train: f = 1 MHz  energy of the micropulses at = 262 nm (UV): E micro = 20…30  J Micropulses have flat- top shape:  duration: 15…25 ps (configurable ) But:  edges:  = 5…6 ps  too long  fluctuation during the flat-top:  = 3…8%  too large Streak camera record of the UV output pulses Courtesy I.Will (MBI)

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ 27

9-11/10/2006 ICW Workshop SLAC J.Bähr, DESY, PITZ Photocathode laser Courtesy I.Will (MBI)