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EO@BC2 – A robust bunch length monitor. Comissioning and first results of a possible standard diagnostic tool. Laurens Wissmann Bernd Steffen, Jonas Breunlin EO@BC2 – A robust bunch length monitor FLASH seminar , 2011-12-20. Outline. Basics

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eo@bc2 a robust bunch length monitor

EO@BC2 – A robust bunchlengthmonitor

Comissioningandfirstresultsof a possiblestandarddiagnostictool

Laurens Wissmann

Bernd Steffen, Jonas Breunlin

EO@BC2 – A robust bunchlengthmonitor

FLASH seminar, 2011-12-20

outline
Outline
  • Basics
    • The electro-opticeffect, measurementsetups
    • Electro-opticspectraldecoding
  • Setup
    • Schematic
    • Laser systemandlasersynchronisation
    • Electro-opticfrontend, electronics
  • Results
    • EstablishingOverlap
    • Data acquisition, time calibration
    • Long rangescan, lowchargecapability
    • Beam shapemeasurement vs. LOLA, resolutionlimitation
  • Upgrade
    • Exchange of EO crystal, newresults, summary

Laurens Wissmann – EO@BC2 – Page 2/18

electro optic effect
Electro-OpticEffect
  • Electricfieldofrelativisticelectronbunch: THz-pulse in laboratoryframe
  • THz pulse changesrefractiveindex in the EO crystal
  • Polarisation of a copropagatinglaser pulse accordinglychanges
  • For example: crossed polariser setting (CP) picturedhere
  • Analyserchangespolarisationmodulation in amplitudemodulation

Laurens Wissmann – EO@BC2 – Page 3/18

measurement s etups
Measurement Setups
  • EOS – electro-opticsampling
    • Least complex
    • multishottechnique
    • lowlaser power necessary
  • EOTD – electro-optic temporal decoding
    • Most complex
    • singleshot
    • requires ~100 µJ laserpulses
  • Other – EOSpD, Frequencymixing, etc.
  • General temporal resolutionlimitations:
    • EO crystalresonances
    • Laser pulse length

Laurens Wissmann – EO@BC2 – Page 4/18

eosd electro optic s pectral d ecoding
EOSD – Electro-OpticSpectralDecoding
  • Short laser pulse has a broadbandwidth (0.1 ps at 1030 nm => 10 nm)
  • Chirped pulse: not transform limited, frequencycomponentssorted
  • Chirpedlaser pulse copropagateswiththeTHzfield in thecrystal
  • Different spectralcomponentsacquire different polarisationmodulation
  • Translation intoamplitudemodulation, readout via spectrometer
  • Medium complex, singleshot, requires large bandwidthlaserpulses
  • Resolution limited toΔ by frequency mixing

Laurens Wissmann – EO@BC2 – Page 5/18

eo@bc2 s etup schematic
EO@BC2 Setup - Schematic
  • All components in tunnel
  • Lead shielded box for
    • Laser
    • Electronics
    • Readoutcamera (10 Hz)
  • Remote control on
    • Crystal-to-beam-position
    • Analyserwaveplatesetting
    • Laser status
    • Laser synchronisation
    • Laser-to-bunchtiming

Laurens Wissmann – EO@BC2 – Page 6/18

eo@bc2 s etup y tterbium doped f ibre l aser ydfl
EO@BC2 Setup – Ytterbium DopedFibreLaser (YDFL)
  • Commercial system (Menlo)
  • Ytterbium-dopedfibrelaser
  • Very robust design
  • Virtuallynomaintainance
  • Pulse lengthchirpedto7 ps

Laurens Wissmann – EO@BC2 – Page 7/18

eo@bc2 s etup ydfl synchronisation
EO@BC2 Setup– YDFL Synchronisation
  • Temperaturestabilisedlaser
  • Cavitylengthadjustment
    • Rough: Motor actuator
    • Fine: Piezo fibrestretcher
  • VME based digital controlloop
  • Goodlongtermperformance (days, weeks,…)

Laurens Wissmann – EO@BC2 – Page 8/18

eo@bc2 s etup the electro optic f rontend
EO@BC2 Setup – The Electro-OpticFrontend
  • Designedat PSI
  • Installedduring 2010 shutdown
  • Equippedwith all necessarybulkoptics
  • Requires 20 cm beam pipe
  • Fibrecoupled, motorised
  • Different dive-in depthswithoutadjustingoptics
  • Wave platesmotorised
  • EO crystal: 0.5 mm GaP

Laurens Wissmann – EO@BC2 – Page 9/18

eo@bc2 s etup electronics t rigger and readout box
EO@BC2 Setup – Electronics, Trigger, andReadout Box
  • Lead shielded box with
    • YDFL, spectrometerandInGaAs Cam
    • RF electronics, AOM
    • Power supplyunitwith piezo driver
    • VME cratewih RF lock controlrunning on a DSP, delaycards, ADC`s, triggerenhancementboard, AOM driverboard
    • Laser power supplyunit
    • 95/5 Coupler, Photodiode, RF amplifiers, otherstuff
    • SRS DG535 for Gate generation
    • Fibrelengthtooptical front end: 2 m

Laurens Wissmann – EO@BC2 – Page 10/18

measurements establishing overlap
Measurements– EstablishingOverlap
  • Fine timing: scanlaser in stepsof 1 ps w.r.t. bunch, lookatcameraand PD
  • Oncefound, timingdoes not changemuch
  • Roughtiming: comparepick-upantennasignaltolaser pulse arrival time
  • Set correcttimervalue for AOM and Cam

Laurens Wissmann – EO@BC2 – Page 11/18

measurements data acquisition and time calibration
Measurements – Data Acquisitionand Time Calibration
  • Reference spectrumtaken
  • Modulatedspectrumtaken
  • Phase retardationiscalculatedfromtheirrelation
  • Phase retardationis proportional totheTHzfieldstrength
  • Time calibrationbyshiftingthelaserwithrespecttothee-bunch
  • -28 channel/ps (bunchhead on theright)
  • 6.4 ps detectorrange

Laurens Wissmann – EO@BC2 – Page 12/18

measurements l ong t ime s can l ow charge a bility
Measurements – Long Time Scan, Low Charge Ability
  • Subsequent setsofdata, concatenated after requiry
  • Clearlyvisibleartifactat 11 ps due toreflection in EO crystal
  • Ringing for severalhundredps
  • Signals for bunchchargesaslowas 50 pChavebeenmeasured

Laurens Wissmann – EO@BC2 – Page 13/18

measurements bunch shapes eo@bc2 vs lola
Measurements – Bunch Shapes: EO@BC2 vs. LOLA
  • Straight through BC3, measure same bunch
  • Goodagreement in shapemeasurementofordinarybunches
  • Oscillationsoccurwhen a steepedgeisproduced

Laurens Wissmann – EO@BC2 – Page 14/18

measurements resolution l imit
Measurements – Resolution Limit
  • Steepedges -> Oscillationsoccur
  • Frequencymixing
  • Simulationshavebeendone, herewithgaussianbunches

Laurens Wissmann – EO@BC2 – Page 15/18

eo@bc2 upgrade 2011 easter s hutdown
EO@BC2 – Upgrade (2011 EasterShutdown)
  • Crystal exchange
    • 0.5 mm GaP -> 5 mm GaP
    • strongerphaseretardation (larger signal)
    • Shiftofthereflectionartifactfrom 11 ps to 110 ps
  • Longeropticalfibre
    • Strongerchirpedpulses (7 ps -> 10 ps)
    • Enhamncementofthedetectorrange
  • Trigger enhancementboardintegrated
    • Lesstimingjitter for theopticalgating
    • Decreaseofamplitudejitter
  • Laser hadtobereturned a second time

Laurens Wissmann – EO@BC2 – Page 16/18

eo@bc2 c urrent s tatus and o utlook
EO@BC2 – CurrentStatus andOutlook
  • Hardware
    • Monitor provedtoworkasplanned
    • Resolution sufficient for longbunches after BC2
  • Software
    • All measurementsweretakenwith MATLAB scripts -> not userfriendly
    • A Matlab GUI isavailable -> moreuserfriendly
    • A dedicated DOOCS serverisbeingdevelopped -> operatortool
  • Future perspective
    • Usefultuningtool, for example, for tailoredbunches
    • Minor changesmightbeinteresting (integrating a pulse compressor in thefrontend)
    • The frontend will be a partofthe XFEL diagnostics, with a different lasersystem

Laurens Wissmann – EO@BC2 – Page 17/18

the end
The End

Thankyou for yourattention.

…anyquestions?