A Study Of Optical Enhancement Cavity With Short Laser .
1A study of Optical Enhancement Cavitywith short laser pulses forlaser-electron beam InteractionYan YOUJoint PhD student of Tsinghua University and Paris Sud 11 UniversitySeminar at LBNL2014-05-05
ContentsBackgroundX-ray Applications and SourcesTsinghua Thomson Scattering platformLaser-electron Thomson Scattering principleOEC-based X-ray machinesOther applications of pulsed laser injected OECLaser source developmentOptical Enhancement Cavity (OEC) studyLocking studyHTTX OEC system designSummary2
Motivation: X-rays applications and sources3X-ray applications requires high quality source Life science: X-ray Tomographic Microscopy, X-ray crystallography of biological structure& function at the molecular level, Material science: X-ray crystallography of ceramics, powders, agglomerates, Medical diagnosis: Imagery, therapy, X-ray source p01313/fig tab/srep01313 F1.htmlFacilitiesPropertiesCompact light source (CLS)SynchrotronRadiationHigh brightness, high energy electronstorage ring GeV, large device, high costFree ElectronLaserFar exceed brightness, intensity , but highenergy electron Linac, large device, highcost,Compact, relative low costThomsonscattering1012ph/sLength: 12m
Tsinghua Thomson Scattering platform Existing setup: 10TW laser system and 45MeV LINACElectron beam4Laser beamEnergy45MeVWavelength800nmBunch length1 4psPulse duration 50fsCharge 0.7nCPulse energy 500mJBeam size30(H)x25(V)umBeam size 30umMain features:High peak powerLow average powerShort pulse durationHuge pulse energyLow repetition rate: TW-PW: several W: tens of fs: hundreds of mJ: tens of HzTW laserLPWA ChamberThomson chamberThomson scattering: achieved X-ray photon Flux3.4x107ph/sPaper: Generation of first hard X-ray pulse at Tsinghua Thomson Scattering X-raySourceRF gun45MeV LinacLaser plasma wakefield accelerator: obtained10 40MeV high quality monoenergetic electron beamsPaper:Generating 10 40MeV high quality monoenergetic electron beams using a5TW 60fs laser at Tsinghua University
Laser-Electron Thomson Scattering principle𝑁𝛾 𝑁𝑒 𝑁𝑙 𝜎T FrepTens of HzTens of MHz𝜎𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛 2 𝜎𝑙𝑎𝑠𝑒𝑟 2Ne: electron numberNl: laser photon number T: Thomson scattering cross-sectionFrep: colliding repetition rate electron: electron beam size r.m.s laser: laser beam size r.m.s The cross-section for this process isvery low : T 6.65 x 10-33 cm25
OEC based X-ray machineFirst OEC based X-ray machine concept drawingZ. Huang and R.D. Ruth, Laser-electron storage ringR. J. Loewen, thesis OEC recycle laser accumulate the laser power Enhancement factors on the laser power:103 104Main features:High average laser power: kW-MWHigh colliding rate: tens of MHzHigh X-rays flux : 1011-1013 ph/s6
1.4-H-LEXM research UpdatesOEC based X-ray machine statusJ. Abendroth et al. J Struct FunctGenomics 11:91-100(2010)7ThomX-Conceptual Design ReportLyncean TechK. Sakaue et al. Proceedings ofEPAC 2006, THPCH154ThomXLUCXFacilityElectron energy [MeV]X-ray Energy [keV]Flux [ph/s]SizeLyncean Tech/SLACIn operationKEK:LUCXIn operationLAL: ThomXUnder constructionUkraine: KIPTProposal20–45305040-225Present :1050-906-900Present :1051011-10131013 10m LINAC10m x7m total sizeExpected :7-35Present: 10-20Expected :1013Present: 101212 m length
Other applications of pulsed laser injected OECApplicationDetailInstituteThomson scatteringγ-rays sourceKEK, LAL, SLAC, KIPTLaser wireLow emittance electron beam size monitorKEKPolarimeterelectron beam polarity diagnosticDESYHHGsoft X-ray source, XUV lightJILA, MPIFrequencystabilizationCarrier-Envelope Phase Control of FemtosecondMode-Locked LasersJILA8
OEC system overview9The OEC system can be divided into 7 sub-systems :Laser, OEC, Optical setup, Electro-optical setup, Locking(Feedback) , Mechanics, Diagnostictools.Cavity to e- clock lockingExternale- clockFeedback BLaser Frep usedas cavity FSRPulsedLASERe- ringInteractionPoint (IP)OPTICSElectroOpticsPZTPZTOECFeedback ATrigger (resonance)Laser to cavity lockingBlock diagram of the OEC sub-systems
10ContentsBackgroundLaser source developmentMode-locked fiber laser developmentOptical Enhancement Cavity (OEC) studyLocking studyHTTX OEC system designSummary
Mode-locked fiber laser construction11outputCollimatorcollimatorQWP PBSYb-fiberPSCCollimatorpumpLD protectorPicture of the laser Self-starting mode-lockingfrep 18.9MHzSetup layout of the mode-locked Yb-doped fiber laser based onNonlinear polarization rotation 20nm Pulse duration 300fs Output pulse power 65mWto 170mWY. You et al, IPAC13
Mode-locked fiber laser design12Laser type @ hundreds of MHz: solid-state -10W; Yb-doped fiber laser-420W, high powerFiber laser low cost compared to the solid-state laser- best candidate for laser source of OECH. Carstens, et al, Optics Letters.,39, 2595-2598 (2014)Mode-locking method- Nonlinear polarization rotation(NLPR)A power-dependent polarization change isconverted into a power-dependent transmissionthrough a polarizing optical element.Advantages:Easy to implement, no need saturable absorbers,applicable to high power outputDisadvantages:optimum polarization settings can drift withtemperature and fiber bends, suffers frompolarization changesA. Hideur, et al. Appl. Phys. Lett. 79, 3389 (2001)A. Chong et al, Opt.Express 14, 10095 (2006)Cavity configuration:- All-normal dispersion setup Simple setup, only consists of elements with normal GVD, no need to have dispersioncompensation elements Wave breaking free pulse, pulse energy up to about 50 nJ, output power several hundreds mW
13ContentsBackgroundLaser source developmentOptical Enhancement Cavity (OEC) studyLocking studyHTTX OEC system designSummaryOEC geometryPulsed laser-OEC stackingCavity waist size measurement
Cavity geometry14Criteria : stable geometry small waist size easy to install and control2-mirror4-mirror2Dsimpler design but concentricgeometry is mechanically unstablewhen small laser waists are foreseen3DNot applicable6-mirror , 8-mirrorcompared to 2M, mechanically more stableand provides better flexibilities to adjust thecavity round trip frequency and the cavitywaist size.2D compared to 3D, more compact and moreeasy to install2D crossed cavity needs less space forintegration to electron storage ring than the2D bow-tie cavitycompared to 4M cavity, moreunstable elements and morevariable parameters : controlmore difficult to achieve.compared to 2D, same mechanical stability,more difficult to install.4M – 2D crossed cavity2M4M –2D bow-tiebest geometry for stable, small waist, easy to installand control
Pusled laser-OEC stacking15Enhancement : the cavity enhances the laser power by stacking each pulse.The enhancement factor, G, is determined by cavity finesse ℱ : G ℱ/πLaser pulse stacking1frep Trepℱ Lcav𝜋 𝑅𝑒𝑓𝑓1 𝑅𝑒𝑓𝑓Intra-cavity pulsesTrepFSR accumulationM1c2 LcavM2pulsed laser beam: Time domain representation The laser beam repetition rate frep must matchthe Free Spectral Range (FSR) of the cavity.Comb spacing matchingfrep FSRlaserCavity freq. combcavity The laser beam pulses are injected with apulse-to-pulse phase ce(laser-design dependent) The intra-cavity beam pulses acquire a phase 0 in one cavity round-trip (mirror dispersion)pulsed laser beam: Frequency domain representationR. J. Jones et al. Opt. Commun., 175:409-418 (2000)Comb position matching ce 0lasercavity
Cavity waist size measurement based on Gouy phaseTraditional methodNew methodPinhole PDCCDBased on Gouy phaseScan the cavity transmittedbeamCatch the beam profile of thecavity transmitted lightCavity waist size is derived directlyfrom the Gouy phaseUse linear fitting of the transmitted light beam size to evaluate thecavity waist size, accuracy is correlated with the fittingScan the beam,time consumingPrecision is affected by the CCDtrigger timeSimple, accurateGouy phase can be directly andprecisely measured through the AiryfunctionReflected-lightAiry FunctionTEM00TEM00FSRTEM00PZTGouy nd-order1st-order2nd-order16
Cavity waist size measurement based on Gouy phase17Demonstrated the effectiveness of this new method, based on the gouy phase measurement for planarn-mirror cavityCW laserM1IsolatorPDL3w0s: waist size in sagittal plane,w0t: waist size in tangential planeϕs: Gouy phase in sagittal plane,ϕt: Gouy phase in tangential planeL2WaistBeam waist size for 4M cavity:HWPPBS QWP F1M3 L1F2M4PDExperimental setup of 4M CW laser102100Theory wtTheory wsExperiment wtExperiment.ws9896Waist(um) ( ks cos( s ))w 0s sin( s ) w ( kt cos( t )) 0t sin( t ) PZTM2L494929088860.00.51.01.52.0d(mm)Theoretical and experimental results of 4M CW laserY. YOU et al.Nuclear Instruments and Methods in Physics Study A, 694, 6-10 (2012)
18ContentsBackgroundLaser source developmentOptical Enhancement Cavity (OEC) studyLocking studyHTTX OEC system designSummaryLockingPDH and TL introductionTL error signal derivation & simulationTL error signal deformation compensationExperimental setup at LAL, OrsayLocking Functional DiagramTL Experimental resultsTL / PDH comparison
Locking19What is locking?PulsedLASERFSR 0AOMfrep ceOECActuatorTrigger (resonance)ServoLaser to cavity lockingWhy do we need a locking?OscillatorPump laserM8M10M9P1M0M7GTILTi:SaM4M5 M1 MotorP2M6800nmM2 PZTSLITLYOTSTARTERGALVOM3Example of mode-locked oscillator (MIRA, Coherent) laser noise sources: pumplight, mirror position, beamaxis fluctuations The free running mode-lockedlaser cavity fluctuates byseveral nano-meters The stacking conditions cannot be maintained withoutlocking:frep FSR ce 0
Locking20How to achieve locking?PulsedLASERFSR 0AOMfrep ceOECActuatorServoTrigger (resonance)Laser to cavity locking Feedback is scheme to achieve locking. By feeding back the laser frep/fce using its PZT/ AOM, the stacking conditions: frep FSR, and ce 0 are maintained, thus the cavity is kept on resonance.Locking stabilization precision:𝛥𝑓𝑟𝑒𝑝𝑓𝑟𝑒𝑝 10-13Feedback system consists:Sensor (PD)Error signal techniqueAnalog/Digital Regulator (PI, PI²)Actuators (PZT/AOM/EOM/Pump Current)cavity finesse 30 k,relative length control 0.1 pm for a 1 mcavity
PDH and TL introduction21Tilt Locking (TL) techniquePDH technique Commonly used, mature technique Complex setup: error signal is got by electronicmodulation the injected beam anddemodulation of reflected beam MODULATIONINJECTED BEAMEOMCAVITYFirst used to stabilize the CW laser interferometer forgravitational wave detectionSimple setup: error signal is the interferencedifference of TEM00 mode and TEM10 mode on thetwo halves of a Split-Photodiode (SPD)Propose to use TL for pulsed laser injected opticalcavity lockingTEM00TEM00TEM00Off Resonance 1Resonant caseOff Resonance EM00TEM01FMODReflected Signal(Modulated)APLLPHASE FMOD RFLOB ADiff. 0IFFILTERMIXERTEM10BDiff. 0TEM00 ABDiff. 0SPDDEMODULATION to baseband and FILTERINGR. W. P. Drever et al. Applied Physics B. 31,97-105(1983)D. A. Shaddock et al. J. Opt. A: Pure Appl. Opt. 2, 400 (2000)
TL error signal derivation22SPD @far away from waistConcave-concave cavitySPD @ near waist of interferometerPlane-concave cavityWaistWaistSPDSPDTEM10 mode generation(a) Beam tiltedTEM00TEM00TEM10(b) Beam shiftTEM10aLaser axisCavity axisϴCavity axisLaser axisD.Z. Anderson, Appl. Opt. 23, 2944-2949 (1984)SPDTEM10 z , , a, , ws / wz TEM00Perfect alignedGeneral form of error signal formulaSPD transverse offsetY. You et al, Rev. Sci. Instrum. 85, 033102 (2014)
TL error signal simulationAt the waist position, z 0Symmetrical error signal :θ and SPD sizeSPD size vs error signalTilt angle θ vs error signalϴ 10-4 radϴ 2 10-4 radϴ 3 10-4 radws wzws 3wzws 10wzws- SPD active size - laser beam tilt angle0.100.2Amplitude[a.u.]a.u.Error signalAmplitude a.u.ws 2wz0.150.4Amplitude [a.u.]230.00.2wz- laser beam size at y FSR10202010010Frequency/FSRFrequency LinewidthTilt angle and SPD size only affect the amplitude of error signal, symmetrical error size at z 020
TL error signal simulationΔ 0Error signal deformation: z, a, Δa w0/20a w0/10Amplitudea.u.Error signal[a.u.]0.2a w0/5Δ Δ w0/9- w0/9 - SPD transverse offset0.10.00.10.20.3200.210z 00.10Frequency/FSRFrequencyLinewidth1020z 1.0mz 0.1mz- SPD longitudinal 1020Amplitude[a.u.]Errorsignal a.u.Amplitudesignal a.u.[a.u.]Errora- laser beam lateral shift240.10.00.10.220100Frequency/FSR1020
TL Error signal deformation compensation25 a, , , w0 , z, ws / wz a- laser beam lateral shift - laser beam tilt anglez- SPD longitudinal positionw0- Cavity waist size - SPD transverse offsetwz- laser beam size at zws- SPD active sizeDeformed error signalWhat we want is Symmetrical error signalΔ 0Δ 0.1 wzΔ 0.15 wzΔ 0.2wzAmplitudea.u.Error signal[a.u.]0.1ϴ 10-4rada w0/10ws wz0.00.1z 1m0.220100FrequencyLinewidthFrequency/FSR1020
Experimental setup @ LAL, FrancePLICMira laserCavityFSEOM26
Experimental setup @ LAL, Orsay27SPDABCCD 2mPDWa i stMc2M4Mc1Fabry-Perot cavityGlan PrismCoherentVerdi-V6CoherentMIRA oscillatorM5F1EOMλ/4λ/2FIPBSFSPLIC parametersLaser wavelength800 nmLaser repetition rate Frep76.5 MHzPulse duration2 psCavity mirror Mc1, Mc2 curvature2mCavity length Lcav 2 mCavity finesse28 000PDH-PDCoupling-PDλ/4SLITM6F2F3M3
Locking function diagram of PLIC28PDH and TL in one setupPZT for frep control, and FS for fce controlFS Driver(110MHz)LaserEOMcavityFS (AOM)double-passPZT-frepAmplifierP/PIGenerator 1(master)Coupling-PDNear input mirrorSPDPLL-10MHzPI/PIIPZTSELECTGenerator 2 Phase Shift(Slave)ON/OFFPDHFSSELECTPDH-εTL-εPZT and FS selections are independantLPFPD-PDHLOA-BMixerIFTLRF
TL Experimental Results29TL and PDH error signal comparisonPZTPDHTLTRANSTL with DC driftHousing & air-conditioner offTL, PDH error signals and the transmitted signal.Y. You et al, Rev. Sci. Instrum. 85, 033102 (2014)
TL Experimental ResultsTL and PDH locking comparisonBoth TL and PDH: high sensitivity , stable lockingthe cavity more than 1h, and high coupling30 TL is sensitive to beam pointing,environment noises. Low noiseenvironment is s of (a) TL locking, average coupling 80%; (b) PDH locking average coupling 73%.TL shows the same locking ability as PDH, high coupling rate, stable locking in a quiet environment. Demonstrated that TL is applicable in the far field case TL can be used to lock a pulsed laser to a high finesse cavityY. You et al, Rev. Sci. Instrum. 85, 033102 (2014)
TL / PDH Comparison31PDHTLCommentsTechniqueRequires electro-modulation anddemodulation.Use the interference betweenTEM00 and TEM01 modesTL has more simple setupComponents/CostEOM, EOM Driver, two waveformgenerator, Mixer, filterOne SPD, Diff. boardTL is cheaperStabilityVery good.Depend on error signal driftHousing can be a solutionError signalamplitudeDepends on EOM modulationdepth.Depends on the TEM01 modeamplitude.LockingVery stable and long time, onlydepends on laser PZT dynamic.Without drift, seems stable.TL needs more systematicstudyCoupling rate 80% 80%Difficult to compare, itdepends on feedbackconfigurationSensitivityhighhighThe same order ofsensitivityFull spectrumlockingEasy, grating in reflected beampath.Difficult to achieve rightalignment,See my thesis Chapter 4Thesis solution notconvenient.
32ContentsBackgroundLaser source developmentOptical Enhancement Cavity (OEC) studyLocking studyHTTX OEC system designSummaryHTTX machineHTTX OEC system design flowOEC-based X-ray source general setupHTTX-OEC Prototype Literature
HTTX MachineAim: X-ray flux 1010-13ph/sX-ray33OEC system parametersLaserM4M1Q1CavityKickerOutput power10W-100WPulse duration psEnhancement factor104FSR31.25 MHz (9.6m)Power50kW- 500kWCoupling 50%B2aB1a1.3mRF4.8 m RingIPOECB2bB1bQ2HTTX layout (preliminary)M2M3H. Xu, Y. You et al, IPAC13
HTTX OEC System Design Flow34CavitySimple 4M cavity 4M HV compatibleon air pressure cavity on Air pressure2M/4M HV compatiblecavity in High VacuumPLIC (2M)Cavity : 2M, on air, UHVLaser : MIRA 76MHz,modifiedMightlaser (4M)Laser : Menlo 178.5MHzCavity : 4M, on air, UHVFeedback : on-the-shelfelectronics and self-madedigital, PDHLocking : laser to cavityhttx-c-Final-220172013Cavity : 4M, HV compatiblePreliminary tests outsideaccelerator, undervacuumhttx-c-Final-1Preliminary tests outsideaccelerator,in airhttx-p“prototype/design”Cavity : 4M, on air, std mounts,finesse 3000Laser : MIRA 79MHzFeedback : on-the-shelf electronicsAnalog, PDH& TLLocking : laser to cavityhttx-Final-c “Compton”Laser : Solid-State/Fiber LaserFeedback : on-the-shelf electronicsAnalog/digital ?Locking : laser to cavityCavity to ext. clock (e-)2018httx-c-Final-3Preliminary tests in Air,in accelerator20152017httx-p“prototype/tests”Lab (LAL) Air Pressure Lab (Tsinghua) Air PressureLab VacuumTTX AcceleratorLocation
HTTX-OEC Prototype Literature35Topttx-p“prototype/design”Cavity : 4M, on air, std mounts,finesse 3000Laser : MIRA 79MHzFeedback : on-the-shelf electronicsAnalog, PDH & TLLocking : laser to cavityThis document2013ttx-p-001-001Documentation ListSystem Specification Levelttx-p“prototype/tests”ttx-p-002-001Design Processttx-p-002-002System Specificationsttx-p-002-003System Teststtx-p-002-004Gantt Diagramttx-p-002-005User’s ManualSystem Design & Tests LevelPLIC-003-002PLIC design describePLIC-003-003Parts Listttx-p-003-001System Designttx-p-003-001-A12M and 4Mcavity comparettx-p-003-002Setup Layoutttx-p-003-003Device Selection Listttx-p-003-001-A21.8m and 7.2 m cavity compareSub-System Design Levelttx-p-004-000Device ignttx-p-004-003Optical l 005-007Diagnostic/ToolstsetSub-System Tests Levelttx-p-004-007-A1SPD2014
SummaryStudies optical enhancement cavity system:laser source, cavity properties, and lockingdesigned and tested a operational mode-locked fiber laserfound a new method to measure beam waist size for planar n-mirror cavityused the TL technique for a pulsed-laser optical cavity locking successfully36
SummaryThank you37
May 05, 2014 · 4 Electron beam Laser beam Energy 45MeV Wavelength 800nm Bunch length 1 4ps Pulse duration 50fs Charge 0.7nC Pulse energy 500mJ Beam size 30(H)x25(V)um Beam size 30um Tsinghua Thomson Scattering platform Thomson scattering: achieved X-ray photon Flux 3.4x107ph/s Existing setup:
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