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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ 2 Outline 1. Introduction 2. Photocathode Laser 3. Laser beam-line and diagnostics 5. Outlook 6. Summary

30/11/2006 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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen 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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ 5 2. Photocathode laser

30/11/2006 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:  = 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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen 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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ 8 3. Laser beam-line& Diagnostics Laser beam-line at PITZ: length 27m

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ 9 3. Laser beam-line & Diagnostics Whole beam-line Wedge plates Remotely controlled : BSA 2 VirtualCathodes 6 mirrors Wedgeplates Pinhole (not used)

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ 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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ 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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen 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 Hamamatsu S4349

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ 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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen 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 (M.Krasilnikov)

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen 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  Manual use  Usable at different positions Foreseen: Permanent absolute monitoring  see talk M.Haenel (this workshop)

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ 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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen 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 (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 Acknowledgement: to Ingo Will for providing slides

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ 18 End

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen 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!

30/11/2006 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):

30/11/2006 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 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)

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen 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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen 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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen 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!!

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen 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

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ Laser beam-line & Diagnostics

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ Laser beam-line Laser beam-line at PITZ: length 27m

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ 28 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)

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ 29

30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ Photocathode laser Courtesy I.Will (MBI)