Post on 14-Jan-2016
description
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
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Outline
1. Introduction2. Photocathode Laser3. Laser beam-line and diagnostics5. Outlook 6. Summary
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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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
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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
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2. Photocathode laser
mainpulse picker
attenuatorgrating
pulse shaper2-stage
preamplifiermodelocked
oscillator2-stage double-
pass preamplifier
integratedauxiliary
pulse picker
wavelengthconversion
IR -> UV
diode-pumpedbooster
(2 stages)
outputpulses
photo-diode
#1
photo-diode
#2
protectionsystem
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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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
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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 interferencefringes
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
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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
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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
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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
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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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
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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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
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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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
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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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)
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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3. 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: 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)
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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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
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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6. 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
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End
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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4. 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
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completely diode-pumped laser operational at PITZ: - differences to the previously used system -
gratingpulse shaper
3-stagepreamplifier
modelockedoscillator
auxiliarypulse picker
mainpulse picker
wavelengthconversion
IR -> UV
flashlamp-pumpedbooster
(2 stages)
outputpulses
photo-diode
#1
photo-diode
#2
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
mainpulse picker
attenuatorgrating
pulse shaper2-stage
preamplifiermodelocked
oscillator2-stage double-
pass preamplifier
integratedauxiliary
pulse picker
wavelengthconversion
IR -> UV
diode-pumpedbooster
(2 stages)
outputpulses
photo-diode
#1
photo-diode
#2
protectionsystem
diode-pumped boosters (new system):
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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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)
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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3. Laser beam-line & Diagnostics
Remotely controlled elements BSA Pinhole 1 switchable mirror 2 cameras
16 axes: rotation or translationAdditional elements on laser diagnostics trolleyElectronics 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
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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
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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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!!
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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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
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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3. Laser beam-line & Diagnostics Properties of laser beam
Property Measurement Tuning Pulse number oscilloscope Laser control Pulse intensity a) power meter Attenuator on laser
table b) PM relative
monitoring
Transverse profile a) virtual cathode VC1, VC2 (for
diff. pulse energy)
b) TV system on laser table
Inclination of converter crystals
Laser beam inclination on laser
table
TV system on laser table
Mirror on laser table
Laser beam diameter VC1, VC2 Beam shaping aperture
Beam on virtual cathodes
VC1, VC2 x,y drive
Longitudinal profile Streak camera Pulse shaper Laser beam position Quadrant diode M4, wedge plates Intensity envelope of
pulse train oscilloscope Laser control
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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3. Laser beam-line
Laser beam-line at PITZ: length 27m
30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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Capabilities of the laserLaser 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 micropulsesat = 262 nm (UV): Emicro = 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
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30/11/2006 Workshop on Laser Pulse Shaping, Zeuthen J.Bähr, DESY, PITZ
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2. Photocathode laser
mainpulse picker
attenuatorgrating
pulse shaper2-stage
preamplifiermodelocked
oscillator2-stage double-
pass preamplifier
integratedauxiliary
pulse picker
wavelengthconversion
IR -> UV
diode-pumpedbooster
(2 stages)
outputpulses
photo-diode
#1
photo-diode
#2
protectionsystem
Courtesy I.Will (MBI)