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Chapter 2: Drivers Revision A (July 2007)
2.0 Introduction ...................................................................................... 1
2.1 Pulse Shaping/Integrated Front-End Source .............................. 42.1.1 Pulse Generation ..................................................................... 7
2.1.1.1 Main, SSD, and backlighter channels ........................ 82.1.1.2 Picket option .............................................................. 82.1.1.3 Fiducial channel ......................................................... 102.1.1.4 Pulse-shape setup ....................................................... 112.1.1.5 ACSL v2 software ..................................................... 12
2.1.2 Koheras Laser Source .............................................................. 122.1.3 Aperture-Coupled Stripline (ACSL) ......................................... 122.1.4 Dual-Amplitude Modulator (DAM) .......................................... 13
2.1.4.1 Electrical-pulse inputs ............................................... 142.1.4.2 DC-bias-voltage input................................................ 142.1.4.3 DC-bias control ......................................................... 142.1.4.4 Modulator output ....................................................... 15
2.1.5 IFES Fiber Amplifier (IFA) ....................................................... 15
2.2 Regenerative Amplifiers ................................................................... 18
2.3 Smoothing by Spectral Dispersion (SSD) ........................................ 21
2.4 Large-Aperture Ring Amplifier (LARA) ......................................... 23
Table of Contents
S-AA-M-##
System Operations Manual Volume I–System Description
Chapter 2: Drivers
��
OMEGA Operations Manual — Volume IRevision A (July 2007)
2.5 Fiducial Subsystem ............................................................................. 262.5.1 ODR and ODR+ ........................................................................ 272.5.2 Fiducial Frequency Conversion ................................................ 282.5.3 Fiducial Delivery ....................................................................... 28
2.6 Hardware Timing System ................................................................... 29
2.7 Laser-Driver Diagnostics .................................................................. 302.7.1 Laser-Energy Measurements ..................................................... 312.7.2 Pulse-Shape Measurements ...................................................... 312.7.3 Pulse-Timing Verification and Pockels Cell Timing Jitter ........ 322.7.4 Spectral Bandwidth and Central Wavelength from SSD .......... 332.7.5 Pointing and Centering Diagnostics .......................................... 33
2.8 Laser-Driver Controls ...................................................................... 352.8.1 Configuration ............................................................................ 352.8.2 ACSL v2 Software .................................................................... 37
2.9 References ............................................................................................ 37
Chapter 2: Drivers July 2007 — Page 1 of 37
Chapter 2Drivers
2.0 Introduction
The Laser Drivers subsystem consists of four distinct driver lines or “drivers;” three that can be injected into the OMEGA beamlines and one that provides an optical timing reference used by diagnostic instruments. Each driver includes the equipment needed to generate, shape, amplify, propagate, and diagnose infrared pulses. The pulses range in duration from 100 ps to 4 ns and are delivered at a rate of 5 Hz.
The names of the driver lines that seed the OMEGA beamlines are historical and do not definitively reflect their capabilities and uses.
• The“main”driverisabasicconfiguration.
• The“SSD”driverissimilartothemaindriverandisoutfittedfortwo-dimensionalsmoothingbyspectraldispersion(SSD).Becausesmoothingcanbeturnedonoroffwithinminutes,thisdrivertendstobeusedforthemajorityofshots.
• The“backlighter”driverissimilartothemaindriver,butisconfiguredtobeinjectedintoanyoneofthethreeOMEGAbeamlinelegs.Thisallowsupto20beamstohaveapulseshapeandon-targetarrivaltimethatisdifferentfromthatoftheremainingbeams.Whilethesebeamsareoftendirectedtotargetsthatproducexraysthatbacklightothershottargets,theyarenotlimitedtothatuse.
EitherofthemainorSSDdriverscanbeinjectedintothestage-Asplitterandonintothethreebeamlegsviaa64-mmboosterlaseramplifier.The“64”makesupfortheenergylossatthethree-waysplitso thatpulseswith identicalshapes, timing,andenergymaybepropagatedonward.When thebacklighterdriverisinuse,themainortheSSDdrivercanbeusedineitherorbothofthelegsthatarenotseededbythebacklighterdriver.
Figure2.0-1providesanoverviewofthecomponentsthatmakeupeachofthedriverlines.Eachdriverhasaseparatelasermasteroscillatorthatprovides1053-nmopticalpulsestotheaperture-coupledstripline(ASCL)equipment.ElectricalsignalsoriginatingintheHardwareTimingSystem(HTS)areusedtogeneratesynchronizedtriggersthatcausetheACSLequipmenttoproducetime-varying(“shaped”)opticalpulses.Thisconfiguration is the resultofan integrated front-endsource (IFES)project thatintroducedthelasermasteroscillatorandtheIFESfiberamplifier(IFA).TheIFAandimprovedACSLcomponentsaregroupedintoasinglerack-mountpackagereferredtoasthe“IFESBox.”
Themain,SSD,andbacklighterdrivers includeanOMEGAdiode-pumpedregenerative (ODR)amplifier,andaflash-lamp–pumped,large-apertureringamplifier(LARA).Thefiducialdriverisusedasatimingreferencefordiagnosticsandhasadifferentamplificationscheme(seeSec.2.5,FiducialSubsystem).
OMEGA System Operations Manual — Volume IPage 2 of 37 — Revision A
The laser-driver subsystems are located in theDriverElectronicsRoom (DER), the PulseGenerationRoom(PGR),andthedriver-linearea(DLA)oftheLaserBay.TheDERandPGRarelocatedwithin the same electromagnetic-interference-shieldedwalls, but have separate heating, ventilation,andair-conditioningsystems.Inadditiontothepulse-shapingsubsystems,theDERhousestheHTS,alongwithvarioustimingcircuits.TheDERandthePGRarefiber-opticallycoupledforflexibilityandalignmentinsensitivity.ThePGRcontainsseveralmajorelementsofthedriverline, includingpulseswitch-out,regenerativeamplification,pulsetruncation,driverdiagnostics,amplification,smoothing,andalignment.
G7361J1
cw masteroscillator
Synchronizationsignals from
hardware timing system
Diode-pumpedregenerative
ampli�er (ODR)
Large aperture ringampli�er (LARA)ODR +
Timing and triggerequipment
IFES box
Shaped optical pulse
Aperture-coupledstripline (ACSL)
equipment
Integrated �berampli�er
38MHz
300Hz
5 Hz
FiducialIR and green users
UV users
nJ (in)
(Main, SSD, backlighter)OMEGA beams
5 Hz
Figure 2.0-1A block diagram of the equipment that makes up a typical driver line. An oscillator provides a continuous-wave signal. Timing signals from HTS are provided to create, shape, and synchronize a pulse train that is amplified for use in the laser system. The fiducial driver line uses a second diode-pumped regenerative amplifier (ODR+) instead of a LARA.
Chapter 2: Drivers July 2007 — Page 3 of 37
DirectlyabovethePGR,attheeastendoftheLaserBay,isthedriver-linearea,whichconsistsofseveralopticaltablescontainingthethreelarge-apertureringamplifiers(LARA’s)andassociatedequipmentthatareusedtoamplifythelaserseedpulseforinjectionintothebeamlines.Figure2.0-2providesanoverviewoftheseitems.
TheopticalpulsesusedtodrivetheOMEGALaserSystemaregeneratedcontinuouslyatarateof300HzintheDER,wherethepulsesoriginateandareshaped(seeFig.2.0-1).ThepulsesaresenttothePGRviafiber-opticcables,wheretheyareamplifiedbyregenerativeamplifiers(regens)atarateof5Hz.The100-pJ/nsoutputsfromeachregenareseparatelydirectedupward,viaaverticallymountedperiscope,tothe40-mmLARA’sinthedriver-linearea.OneLARAisprovidedforeachofthemain,SSD,andbacklighterpulses.EachLARAiscapableofprovidingagainofupto20,000infourround-trips,butisoperatedatalowergaintoincreasethelifeoftherods.
EithertheSSDormaindriverisselectedbythepositionofakinematicmirrorforinjectiontoOMEGA.PriortoleavingtheDLA,theselecteddriver(mainorSSD)isamplifiedto~4Jbythe64-mmrodamplifier.Thepulseisthenspatiallyfilteredandinjectedtothestage-Abeamsplitter,wherethedriver-linepulsesaresplitthreewaysandpropagatedintotheOMEGApoweramplifiers.
G3472bJ2
Fiber
Driver Electronics Room Laser Bay
To A-stageampli�ers
Driver ASP64-mm amp
Regens
SSD
ASP
Backlighter
SSD
Pulse-Generation Room
Backlighter LARA
Fibers
MainIFES
SSDIFES
BLIFES
FiducialIFES
SSD LARA
Main LARA
Kinematicoptical switch
(selects 1 LARA)To �ducialin Target Bay
3
Main
SSD equipment
Figure 2.0-2A block diagram of the laser-driver subsystem. The equipment is located in three areas: Driver Electronics Room, Pulse-Generation Room, and the Laser Bay. The fiducial driver line is located in the Target Bay.
OMEGA System Operations Manual — Volume IPage 4 of 37 — Revision A
Thebacklighterdrivergeneratesa1.4-JlaserpulsecapableofdrivingoneofthethreelegsfromtheA-splitinlieuofthemainorSSDdriverpulses.Thebacklighterpulsearrivesatthestage-Asplitterbyapaththatisseparatefromthatusedbytheotherdrivers.
DrivercontrolsconsistofseveralSunworkstationsandPC-compatiblecomputerstooperateandmonitorcriticaloperatingparameters,diagnostics,andapplicationswithinthedriverssubsystem.Thesecomputersconnecttoperipheralequipmentbymeansofthegeneralpurposeinterfacebus(GPIB),localoperatingnetwork(LON),ordirectlyviaserialports.EachcomputercommunicateswiththeLaserDriversExecutive,whichcontainsdevicecontrol,energydiagnostics,accesstoimaging,andvariousGUI’s.Theexecutivealso interactswith theShotExecutiveusing theproprietaryOMEGAintercommunicationprotocol(OIP)overethernet.
2.1 Pulse Shaping/Integrated Front-End Source
Thepulses for each driver originate in theDER,where a commercially availableKoherasAdjustik®1053-nm,single-wavelength,distributed-feedbackfiberlaserservesasthecwmasteroscillatorforeachchannel.Thelaserisinherentlysinglemodewithastablewavelengthandrequiresnoopticalalignmentfromthephotongenerationtotheregenfiberlaunch.Shapedpulsesareprovidedbyanall-fiber-opticintegratedsource.Theintegratedfront-endsource(IFES)generatesanopticalpulseinthe100-pJrangeusing:acompact,stable,single-frequencyfiber,distributed-feedbacklaser;duallithiumniobatemodulators;andahigh-gainpolarization-maintainingfiberamplifier.ComplexpulseshapesarecreatedbyusinganACSLpulse-shapingsystem,housedwithintheIFESbox.
Section2.1.3describestheconceptoftheACSLandhowthismicrowaveradiotechniqueisappliedtoproducethetime-varyingelectricalsignalsthatareusedtoshapeopticalpulses.StriplineassembliesforeachofthepulseshapesthatcanbeusedonOMEGAhavebeendesignedandtestedandareavailableforinstallationintheIFESbox.TheshapeoftheapertureineachoftheseassemblieswasdesignedbyusingacomprehensivecomputermodeloftheOMEGAsystemtodeterminetheIRtemporalprofilerequiredtoproducetherequiredon-targetUVprofile.Figure2.1-1illustratesthepredictedchangesthatoccurtothepulseshapeoftheIRinputfromtheDLA(ingreen)comparedtotheIRoutput(inred)tothefrequency-conversioncrystalsandtheUVoutput(inblue)atthetarget.
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mal
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UV output
IR input
Figure 2.1-1A temporal pulse shape in the 0.1-5 ns range is critical to the safe operation of OMEGA. Gain saturation in the IR along with the intensity-dependent frequency-conversion efficiency reshapes the temporal pulse shape. High-dynamic-range measurements at the input and a good predictive capability are required to accurately set the on-target pulse shape.
Chapter 2: Drivers July 2007 — Page 5 of 37
Figure2.1-2showsfourtypicalpulseshapesusedinOMEGA.TheappropriatestriplineassemblyisinsertedintotheIFESboxfortherequireddrivertoproduceapulsetrainattherateof300Hz,withthedesiredshapeandwidth.TheshapedoutputpulseisthensenttothePGRandinjectedintoregensforthefirststageofamplification.
G7363J1
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er (
W)(
×10
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)(×
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1
2
3
4
5
6
(a) (b)
(c) (d)
Figure 2.1-2Four examples of OMEGA pulse shapes. (a) SG1018—flat 1-ns pulse, (b) ALPHA201P—picket pulse, (c) SG3702—flat 3-ns pulse, and (d) RR1501—1.5-ns reverse-ramp pulse. The red traces indicate the predicted IR pulse shape in the F-stage prior to the frequency-conversion crystals. The blue traces indicate the predicted UV pulse shape on the target.
ThepulseshapingequipmentforallfourdriversisrackmountedintheDER.Figure2.1-3showsthelayoutoftheDERracks.Racks2,3,and4containtheIFES/ACSLpulse-shapingsystemsforthebacklighter,fiducial, andSSD,and themaindrivers, respectively.Racks1and6containHardwareTimingSystemequipment.Rack5containsvideoequipment.
Figure2.1-4 shows thephysical layoutof theOMEGAIFESchannelswith their associateddiagnosticequipment.Eachdriversourceislocatedinasinglerack.Theserver—ecleto—ismountedonthewallinfrontofRack4.Eachmoduleinthesubsystemisconnectedviafiber-opticcables.Thepulsestravelthroughfiber-opticstrandsanddonotrequireclean-roomfacilitiestoprotectthelaserseedpulsesfromenvironmentalcontamination.
OMEGA System Operations Manual — Volume IPage 6 of 37 — Revision A
G7366J1
Rack 1
Storage
Rack 2
Rack 3
Rack 4
Power conditioning shop
Plenum PGR
OMEGA main hallwayNorth
Garment
Rack 5
Rack 6
G7369J1
Main PSPL 35 volt box
Main PSPL 10 volt box
Main Colby 10
Main Colby 40
HP In�nium o-scopetiming (Rowlett)
Main Koheras
Main IFES
MainILX lightwave
LDX 3545current source
MainILX lightwave
LDT 5525temp control
Main wavemaster
Fiber management
DSC 50 power supply and monitor
Tektronix TDS 8200digital sampling
oscilloscope
ACSL/pulse shaping
RACK 4
SSD Colby 40
SSD Colby 10
SSD Koheras
SSDILX lightwave
LDX 3545current source
SSDILX lightwave
LDT 5525temp control
SSD wavemaster
Tektronix TDS 6154Cdigital storageoscilloscope
SSD PSPL 10 volt box
Picket PSPL 10 volt box
Picket Colby 40
SSD PSPL 35 volt box
SSD IFES box
Keyboard tray for tektronixTDS 6154C
Cooling fan (9 unit)
RACK 3
BacklighterILX lightwave
LDX 3545current source
BacklighterILX lightwave
LDT 5525temp control
FiducialILX lightwave
LDX 3545current source
FiducialILX lightwave
LDT 5525temp control
Fiducialtrombone
Backlighterwavemaster
Fiducial PSPL 10 volt box
Fiducial PSPL 35 volt box
Fiducial IFES box
Backlighter Colby 40
Backlighter Colby 10
Backlighter PSPL 10 volt box
Backlighter Koheras
Fiducial Koheras
Backlighter PSPL 35 volt box
Backlighter IFES box
Comb generator912 MHz
RACK 2
Figure 2.1-3The DER floor layout. The IFES equipment is located in Racks 2 through 4 (shaded). The Power Conditioning shop is located between the DER and Capacitor Bay 2.
Figure 2.1-4Physical layout of the IFES racks in DER with open space omitted.
Chapter 2: Drivers July 2007 — Page 7 of 37
2.1.1 Pulse Generation
Thebasiccomponentsineachchannelaretwoelectricalsquare-wavepulsegenerators,adelaygenerator,anACSLassembly,andadual-amplitudeopticalmodulator,allfedbyaKoherascwlaser.
Figure2.1-5showsablockdiagramofthepulse-generationprocess.AKoherasmasteroscillatorprovides1053-nmcontinuous-wavelaserenergytothedual-amplitudemodulator(DAM).TheACSLv2softwarecontrolsthepulse-shapingprocesswithinIFES,includingthedcbias-controlvoltages.
Manualcontrol
Isolator
PSPL 35 V
G7370J2
Diodelaser
Controlelectronics
Controlelectronics
Thermallystabilized
Yd-doped �berBragg grating
Isolator
Koheras CW master oscillator
ACSLscope
Diodelaser
Yb:�berFaraday
mirror with�lter
Integrated �ber ampli�er(CW-pumped)
1030�lter WDM
90/10
Ecleto
Bias control
RS-232
Dual amplitude modulator
DC1 DC2
E/O
Fiber
Aperture-coupledstrip line
Wavelengthmeter
ModulatorColby 40
Colby 10
PSPL 10 V
To regens
MOD1gate-pulseinput
MOD2 shaped- pulse input
Fiber
300 Hz300 Hz
38 MHz
Polarizingbeam
splitter
Figure 2.1-5A block diagram of the main and backlighter pulse generation process in DER.
OMEGA System Operations Manual — Volume IPage 8 of 37 — Revision A
The38-MHzreferencefrequency(RF)fromtheOMEGAHardwareTimingSystemisfedintoaColby40programmable,mechanical,delay-lineinstrument,withastandarddelayextensionrangeof40ns.Usingtheinternaldelayline,theColby40controlsthephasingoftheRFinputtothe10-Vpulsegeneratorwithanaccuracyofwithintensofpicoseconds.
The10-VamplitudeDAMgatesignalisgeneratedbyaPicosecondPulseLabsProgrammablePulseGenerator(PSPL10V).TheoutputofthepulsegeneratorissynchronizedtoOMEGAusingthe38-MHzand300-Hzelectricalinputs.The300-HzgateinputcomesdirectlyfromtheHTS,andthetriggerissynchronouswiththe38-MHzRFdistributionthroughtheColby40.The10-Vpulsegeneratorusesthe300-Hzelectricalgatetoenablethetriggercircuit,whichlooksforthenextpositiveslopezerovoltcrossingfromthe38-MHzsignal.IfeitheroftheinputsignalstothePSPL10Visabsentorifthepulserisdisabled,theoutputtriggerpulsewillalsobedisabled.TheACSLv2softwarecontrolstheoutputtimingbymakingtwoadjustments;courseoutput-timingadjustments(with26-nsresolution)tothe300-Hzgateinput,andprecisetimingadjustmentstotheelectricalphaseoftheRFsignalusingtheColby40RF-programmabledelaylineoverarangeof13.1ns.
The process of providing the signal to the aperture-coupled stripline is unique for eachconfigurationandwillbediscussedindividually.Theshapingofthepulsesisachievedbyusingtheshaped-pulseinputfromthestripline.Eachaperture-coupledstriplineisdesignedtoproduceaspecificelectricalpulseshapethatdrivesanopticalmodulatortoproducethedesiredopticalpulse.
Inordertoachievethedesiredpulseshape,itiscriticaltosetupapulseusingtheconditionsforwhichthestriplinewasdesignedtooperate.
2.1.1.1 Main, SSD, and backlighter channelsThe same optoelectronic hardware configuration is used for the main, backlighter, and SSD
pulse-shaping channels. In each case, precise optical pulses can be generated by the combination of a properly defined stripline and a suitable gate.
A 10-V square-pulse generator (PSPL 10V) is used to produce the electrical gate signal applied to the MOD1 port of the modulator (see Fig. 2-1.5). The optical pulse shape is determined by the electrical waveform, as defined by the aperture dimensions in the stripline.
The 10-V pulser-trigger output feeds the gate channel as well as the pulse channel. For the pulse channel, this input passes through a 10-ns delay (Colby 10) into the trigger input of a 35-V Picosecond Model 4500E Step Generator (PSPL 35V). This 35-V square pulse is fed to the ACSL. The PSPL 35 provides extremely stable pulses with a fast rise time of 100 ps, to a high amplitude of 35 V with only 1.5-ps of jitter.
2.1.1.2 Picket optionThe “picket” option permits the addition of a short optical pulse (picket) to a shaped pulse. This
channel type is an adaptation of the SSD channel type and is produced by reconfiguring hardware from the SSD pulse-shaping channel (see Fig. 2.1-6).
Chapter 2: Drivers July 2007 — Page 9 of 37
Manualcontrol
Isolator
PSPL 35 V
G7370J3
Diodelaser
Controlelectronics
Controlelectronics
Thermallystabilized
Yd-doped �berBragg grating
Isolator
Koheras CW master oscillator
ACSLscope
Diodelaser
Yb:�berFaraday
mirror with�lter
Integrated �ber ampli�er(CW-pumped)
1030�lter WDM
90/10
Ecleto
Bias control
RS-232
Dual amplitude modulator
DC1 DC2
E/O
Fiber
Aperture-coupledstrip line
Wavelengthmeter
ModulatorColby 40
Trigger amp
Colby 40
Modi�edPSPL 10 V
Modi�ed PSPL10-V picket
To regens
MOD1gate-pulseinput
MOD2 shaped- pulse input
Fiber
300 Hz300 Hz
38 MHz
Polarizingbeam
splitter
To timing diag
Figure 2.1-6A block diagram of the SSD picket-option pulse-generation process in DER.
OMEGA System Operations Manual — Volume IPage 10 of 37 — Revision A
The picket process is set up on the SSD pulse-shaping channel by disconnecting the 50-ohm termination on the back of the stripline and replacing it with the output of the modified PSPL 10V picket box. This allows a “picket” to be formed on the leading edge of the pulse. The pulse width is controlled by a fixed electrical differentiator after the PSPL 10V picket box. Picket amplitude is controlled by attenuation to the picket electrical signal applied to the modulator. A trigger amp is used to split the PSPL 10V output and send it on to the PSPL 35V that feeds the aperture-coupled stripline, and to a Colby 40 used to adjust the picket-timing control. The picket signal is generated by the modified picket PSPL 10V unit.
2.1.1.3 Fiducial channelThe fiducial channel produces a series of eight optical pulses spaced 0.5 ns apart in time.
Diagnostic instruments used on OMEGA rely on these pulses as a timing reference (see Fig. 2.1-7).
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Figure 2.1-7The fiducial “comb” consists of eight pulses that are 0.5 ns apart.
A comb generator produces high-frequency electrical pulses. These pulses are applied to the MOD2 port of the modulator, and a gate-pulse is applied to the MOD1 port of the modulator (see Fig. 2.1-8). The fiducial gate width is unique from the other drivers in that the shape is determined by the stripline, controlling the number of optical pulses produced by the first modulator that are allowed to pass through the second modulator. The output of its 10-V pulse generator (PSPL 10V) provides a time-base reference for the ACSL diagnostics. This pulse is used to trigger the high-speed sampling scope used to diagnose pulse shapes produced by the system.
A manual radio-frequency trombone is used to delay the trigger output. This manual device minimizes the possibility of device failures that could cause unwanted system-timing-delay changes. Section 2.5, Fiducial Amplifier Subsystem, provides more details.
Chapter 2: Drivers July 2007 — Page 11 of 37
Manualcontrol
Isolator
PSPL 35 V
G7370J4
Diodelaser
Controlelectronics
Controlelectronics
Thermallystabilized
Yd-doped �berBragg grating
Isolator
Koheras CW master oscillator
ACSLscope
Diodelaser
Yb:�berFaraday
mirror with�lter
Integrated �ber ampli�er(CW-pumped)
1030�lter WDM
90/10
Ecleto
Bias control
RS-232
Dual amplitude modulator
DC1 DC2
E/ONEOS
Fiber
Aperture-coupledstrip line
Wavelengthmeter
Modulator
Comb generator
Optical trombone
PSPL 10 V
To regens
MOD1gate-pulseinput
MOD2 shaped- pulse input
Fiber
300 Hz
300 Hz
38 MHz
300 Hz
Polarizingbeam
splitter
Figure 2.1-8A block diagram of the fiducial pulse-generation process in DER.
2.1.1.4 Pulse-shape setupTwo important steps are required to set up a pulse shape
1. Therisingedgeoftheopticalpulsemustoccuratthecorrecttime,and
2. Instrument settings are systematically adjusted until themeasured pulsematches thedesigntemplate.
OMEGA System Operations Manual — Volume IPage 12 of 37 — Revision A
If previous shots have been executed using the desired pulse shape, instrument settings from that shot may be restored from the database. Otherwise, the operator must go through a set-up procedure to achieve the desired results. The set-up procedures, although very similar, are unique for each channel type. The channel types are main, SSD, backlighter, and fiducial. In addition, the SSD channel has a picket option.
2.1.1.5 ACSL v2 softwareTheACSLv2softwareapplication isused tosetup,control,andmonitor thepulse-shaping
process.Theuserinterfaceallowslaser-driverpersonneltoopenagraphicaluserinterfacetoaccessdataandmakenecessaryadjustmentsduringthepulse-shapingprocess.OnlyoneapplicationatatimecanberunonOMEGA.
2.1.2 Koheras Laser Source
TheKoherasAdjustik®systemisacompact,single-wavelengthdistributed-feedbackfiber-lasersystem.The1053.044-nmwavelengthhas0.002%stabilityover24hofoperation,comparedtotherequired0.03%.Thepowerstabilityis0.7%over10hofoperation(Therequirementis<1%over2h).Thenoisefloorwasmeasuredatgreaterthan–57dB,whichiswithinthelimitsofthemeasuringinstrument.
2.1.3 Aperture-Coupled Stripline (ACSL)
Ahigh-bandwidth electrical-waveformgenerator basedon anACSLhas beendesigned andimplementedforpulse-shapingapplicationsonOMEGA.AnexplodedviewofanACSLisshowninFig.2.1-9.
E8416J1
Electrode 1
Transitionregion Coupling region
Cu
Electrode 2
Cufr
fr
fr
frPort 1
z0
z0
Output
InputPort 2
Aperture
Port 4 Port 3
Figure 2.1-9An exploded block diagram of an ACSL.
Chapter 2: Drivers July 2007 — Page 13 of 37
Astriplineconsistsofastackofthreecopperplates,separatedbytwodielectric(insulating)layers.Thecenterplatehasanaperture(hole)ofaprescribedshape.Inuse,a35-VpulseislaunchedfromaPicosecondPulseLabs35Vpulsegeneratorintoport1fromoneendofthestriplineandpropagatesalongelectrode1toport2oftheACSL,andisterminatedat50ohms.Asthesquarepulsepropagatesalongelectrode1,afractionofthepropagatingelectricfieldiscoupledthroughtheapertureintoelectrode2intheoppositedirection.Thefractionofthefieldcoupledbetweentheelectrodesisdeterminedbytheapertureshape.Bytailoringtheaperturewidthalongthelengthofthestripline,anydesiredelectricalwaveformcanbegeneratedattheoutputatport4andsentdirectlytotheelectro-opticalmodulatorsforpulseshaping.Therefore,theapertureshapecontrolstheelectrical-outputpulseshape.
2.1.4 Dual-Amplitude Modulator (DAM)
Anopticalmodulatorchangesitsopticaltransmissionasafunctionoftheappliedvoltage.ThemodulatorusedforACSLrequirestwoelectricalinputs.Thedcbiasvoltageisappliedtoensurezerotransmissionasthenaturalstate:twoelectricalpulsesallowtransmissiondeterminedbythegateandshapetodefineagivenpulseshape.ThepulsesareprovidedtotheDAMfromthe10-Vpulsegenerator(gate)andtheaperture-coupledstripline(shape)(seeFig.2.1-10).
Agate isrequiredto improvetheriseandfall timesof theopticalpulse,control theopticalpulsewidth,andtosuppressprepulseartifactsthatarenotadequatelycontrolledbythefirstmodulator.Ideally,thegatewouldturnonandoffinstantly,permitting100%opticaltransmissionwhileonand0%transmissionwhenoff.Theactualbehavioristakenintoaccountwhendesigningapertures.
The“shape”featureoftheACSLv2softwareisusedtoadjusttheopticalpulseproducedbythestriplinesothatitcoincideswiththedesigntemplate.
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Computer
RS-232-to-optical
Manualcontrol
Energymonitor
Biascontrol
Dual amplitude modulator
Aperture-coupledstrip line
Koherasmasteroscillator
IFES�berampli�erWavelengthmeter
PSPL 10 V PSPL 35 V
MOD1gatepulse
DC1 DC2
MOD2shapedpulse
Figure 2.1-10Block diagram of the dual-amplitude modulator.
OMEGA System Operations Manual — Volume IPage 14 of 37 — Revision A
2.1.4.1 Electrical-pulse inputsThe two pulse inputs control the time-varying optical transmission of the modulator, allowing the
modulator to act like a high-speed optical switch or pulse shaper. The gate channel provides a narrow “window” for the seed pulse to be propagated from IFES to the regen amplifier. This allows the cw seed to be trimmed of any electrical noise, such as prepulse, postpulse, or excessive noise floor signals, immediately before and after the pulse. The shaped-pulse signal adds the pulse shape created by the ACSL to the second modulator stage where the shape is then applied to the gated optical pulse and then sent on to the IFES fiber amplifier (IFA).
2.1.4.2 DC-bias-voltage inputThebiasisgenerallysettominimumtransmissionatalltimes.ApuredcbiascausestheDAM
toquicklyaccumulateunwantedcharge,resultinginadc-biasdriftof~13mV/h.Abalancedduty-cycleapproachwasadoptedtomaintainzero-averageappliedvoltage,whilekeepinginstantaneousvoltageatatransmissionminimum,orothersetpoint(seeFig.2.1-11).ThevalueofVsetisfixed.Thepulsewidths(T)arecalculatedtogetanaveragevoltageofzerobasedontheperiodofthe300-Hzpulse(~3.33ms).
G7378J1
TEqual areas
Vset
V = 0
V = –23.33 ms
Figure 2.1-11Illustration of the balanced duty cycle approach where the average voltage is equal to zero.
2.1.4.3 DC-bias controlThemodulatorbias-voltagefunctionishandledbyACSLv2softwaretodirectlyinputthenew
biasvoltagetothemodulator.Thebiasvoltage(Vabs)establishesthesteady-stateopticaltransmissionofthemodulatorwhennoelectricalpulseisapplied.Theresponserangeis±4.096Vinincrementsof2mV,±1mV,producingarangeof4096counts.
Themodulatorcontrolisusedtoadjustthedc-biasvoltagetoamodulator.ModulatorcalibrationforVmin/VmaxiscontrolledfromtheACSLv2software,whichwillalsorescaletheVmin/Vmaxrangefordifferentmodulatorvalues.ThevoltagescorrespondingtotheVmin/Vmaxtransmissionpointsareaccessedbyselectingthemodulatoricon(seeFig.2.1-12)fromaschematicandsettingtheattributesVmin(dcminimumtransmissionvoltage)andVr(dchalf-wavevoltage).
TheVabsadjustment,showninFig.2.1-12,isusedtoadjusttheactualoperatingvoltage.ThiswillchangetheplacementofVminaroundthenullofthesinewave.Thisisrequiredtofinetunethepulseshapebeforeamplification.
Chapter 2: Drivers July 2007 — Page 15 of 37
Themodulator drift has beenmeasured to be less than10mVover 16h, compared to thespecificationof<30mV.Amanualmodulator-calibrationroutine(ModCal)wasdevelopedtoperiodicallysweepthevoltagesfrom–4Vto+4VtoaccuratelydetermineVminandVr.ModCalisusedtoresetthebiasvoltagetothepropernormalizedrelationshiptoVmin.
2.1.4.4 Modulator outputTheoutputoftheDAMispassedontotheIFA,withasmallportionsplitoffandfedtotwo
diagnosticinstruments:anenergymeterandawavelengthmeter.Theoutputenergyismeasuredonahigh-bandwidthsamplingoscilloscope.OnescopecanserveuptofourACSLchannelssimultaneously.AWaveMasterLaserWavelengthMetercanmeasurethewavelengthofbothcwandpulsedlasersofanyrepetitionrate.Thedisplaycanbesettomeasurefrequencyingigahertz,bandwidthinnanoseconds,oractualwavecount.
BecausetheDAMhastwointernalmodulatorsthatpotentiallyoperateatdifferentVminandVrlevels,thereisinterferenceintheformofsmallamplitude“bell”pulsesgeneratedintheoutputofthemodulatorunit.Thesebellpulsescorrespondtotheamplitudechangesofeachindividualmodulatorbiasvoltage,asillustratedinFig.2.1-13.
Thelargepulsesontheoutputcorrespondtotheelectronic-timingpulsefromtheHardwareTimingSystemandtheleadingedgesoftheDC1andDC2biasvoltages.Thetwobellpulsescorrespondtothezero-crossingoftheDC2andDC1bias-voltageswitchingfromtheVmin(high)statetotheVmin(low)state.ThesebellpulsesarefilteredoutoftheopticallaserpulseintheIFA.
2.1.5 IFES Fiber Amplifier (IFA)
The IFESfiber amplifier (IFA) boosts the shaped-pulse energy from the dual amplitudemodulator(DAM)totheinputenergyrequiredbytheregenerativeamplifier.TheIFAisassembledfromcommerciallyavailableparts.Thefusion-splicedsystemreduceslong-termdegradation.Theamplifieroperateswithcwpumpingthateliminatestimedcomponents.AblockdiagramoftheIFAisshowninFig.2.1-14.
G7379J1
Vmax
Vmin
Figure 2.1-12TheACSLv2 software graphical user interfaceshowsthemodulatorbiassettings.VrreferstothetimebetweenVminandVmax.
OMEGA System Operations Manual — Volume IPage 16 of 37 — Revision A
G7380J1
DC1
DC2
Output
G7381J2
Controlelectronics
DAM
Regen
ACSL scope
Diodelaser
Faradaymirror
with �lterIsolator
Polarizingbeam
splitterWDM1030 �lter
1053 �lter
Yb:�ber
90/10
Figure 2.1-13Illustration of bell pulses that appear on the output of the DAM as a function of the rising and falling edges of the dc-bias voltages. It is more pronounced where the square waves are changing synchronously.
Figure 2.1-14Block diagram of a cw-pumped IFA.
Chapter 2: Drivers July 2007 — Page 17 of 37
TheshapedpulsearrivesfromtheDAMandpassesthroughaninputisolator,apolarizingbeamsplitter(PBS),anda1030-nmfiltertothewavelengthdivisionmultiplexer(WDM),whereitiscombinedwiththecw-diodelasersignal topumptheenergyfor thefiberamplifier.TheYb:fiberprovidestheamplificationcomponentwithintheIFA.ThisfiberisessentiallythesameastheamplificationfiberinsidetheKoherascwmasteroscillator,exceptthatthisfiberdoesnotcontainagratingfactor.
TheshapedpulseenterstheIFAwithapolaritywhichisinherentlyshiftedasitprogressesthroughthesystemcomponents.TheWDMactsasamultiplexerintheinitialdirectionandademultiplexerinthereturndirection.TheFaradaymirroractsasabandpassfilterandreflectorforwavelengthsnear1055nm,andabsorbstheremainingenergy.TheYb:fiberactstoamplifythesignalinbothdirections.Thebidirectionalsignalspassingthroughthefiberdonotinterfereduetothedifferencesinpolarityinthetwodirections.TheinvertedshapedpulsewillreturntothePBSwithapolarityperpendiculartotheinputcreatingtheswitchouttotheoutputfiber,whichfeedstheregenerativeamplifier.
The amplified shaped pulse passes through the 1030-nmfilter (anotherWDM),where any1030-nmlightwillbesplitoff(includingthebellpulsesthatwereintroducedintheDAM),andpasstheremaining1053-nmshapedpulseon toward thePBS,whereapproximately10%issplitoffandsenttotheACSLscopeformonitoringpurposesandtheremaining90%ispassedontotheregen.TheinputisolatorpreventsanyopticalsignalsthatmightpassthroughthePBSinthereversedirectionfromreflectingbackintotheDAM.
TheIFAresidesinsidetheIFESbox,asshowninFig.2.1-15.TheIFAismountedonaremovablefiber-amplifiershelfforeasymaintenanceaccess.TheDAMandACSLareincloseproximitytoprovideshorttransmissionpathsduringtheprocessingofthepulse.
Usingonly3.0mofYb:fiber,theIFAprovides>100-mWpeakpowertotheregenwith<0.2%distortionmeasuredover theflat topofasquarewave in theunsaturatedamplifier. IFESmeets the40-dBprepulsesuppressionrequirement,andtheASEsuppressionbetweenpulsesexceedsOMEGArequirements,with anOSNRof>56dB.The energy stability is<1% rmsover 2 h.The slow-axispolarizationextinctionratioexceeds100:1.
G7382J1
Pump
FM PBS
ISO
Fibe
rco
mpo
nent
s
Fiber spoolsEnergymonitor
Surface-mount
electronics
Fiber ampli�erplatform
DAM
Figure 2.1-15The IFES box contains the aperture-coupled stripline, dual-amplitude modulator, and the IFES fiber amplifier.
OMEGA System Operations Manual — Volume IPage 18 of 37 — Revision A
Asingle-mode,polarization-preservingopticalfiberprovidesthelinkbetweeneachIFES(inDER)andthecorrespondingregen(inPGR).
2.2 Regenerative Amplifiers
Thediode-pumpedregenerativeamplifiers(regenorDPR)forthemain,SSD,andbacklighterarelocatedinthePulseGenerationRoom(PGR).Thefiducialregenislocatedinthetargetbay(thefiducialdriverlineiscoveredinSec.2.5).Theregensareessentiallyidenticalandareusedforpulseselectionandamplification.Reliableperformancerequiresinjectionofahigh-contrast,singlepulse.EachregenisseededbypulsesfromtheirrespectiveIFESintheDER.TheregensaresynchronizedtoeachotherthroughtheHardwareTimingSystem.
Eachdiode-pumpedregencontainsaPockels-cell-enabledtriggerthatprovidesboththecavityinjection trigger and thecavitydump trigger (seeFig.2.2-1).The regencavity is a stable resonatoroperatingintheTEM00mode.Thediodepumpprovidesrepeatablegain.HTStimingtriggersprovidedtothePockelscellsandthepumpdiodesareusedtoselectsinglepulsesfromthe300-HzpulsetraincomingfromtheIFEStoproduceapulsetrainat5Hz.Figure2.2-2showsthelayoutofatypicaldiode-pumpedregenerativeamplifier.
Thesingle-shapedpulseisswitched-outusinganotherPockelscell,whichprovidesimprovedsignal/noisecontrast.ThePockelscells,includingtheirhigh-voltagedrivers,haveflattransmissionwindowsover
E12281J1
Injected-pulsediagnostics
Mode-matchingdiagnostics
Shapedpulse in 90/10
�bersplitter
Faradayisolator
Polarizer
Faradayrotator
Polarizer
m/2m/4Pockels
cellFlat endmirror
Intracavitydynamics
diagnosticsOutputpulse
diagnostics
Polarizer
Regenoutput
AR/ARpickoff
Pockelscell
Flip-inm/2
Pump moduleNd:YLF
Regen resonator
Sphericalend
mirror Aperture
Pumpdiode
Pumpdiode
m/2
Figure 2.2-1Pockels cells (labeled “PC”) are used with the diode-pumped regenerative amplifier to isolate one shaped pulse from the pulse train provided by IFES.
Chapter 2: Drivers July 2007 — Page 19 of 37
5ns.Theonlysignificantdistortionisduetopredictablesaturationcausedbysquarepulsedistortion.Singlepulseenergiesarenominally~1mJaftertheswitch-outPockelscell.Amplitudestabilityofthe5-Hzpulsetrainattheregenoutputisessential.Output-energyfluctuationshavebeenmeasuredat<0.9%rmsover24h.TheperformancerequirementsfortheseregensareshowninTable2.2-1.DiagnosticslocatedinthePGRmeasuretheenergy,timing,alignment,andstabilityoftheregens.Figure2.2-3showstheorientationofthemainandSSDregensinthePGR.
Aftertheregenerativeamplifiers,thepulsesintheSSDdriveraredirectedtotheelectro-opticmodulatorsandgratingsthatinitiatethesmoothingbyspectraldispersion(SSD)process.Thepulsesalwayspassthroughthemodulators;however,theSSDmodulationcanbeeitheronoroff.Figure2.2-4showsthelayoutoftheopticaltablesinDER.
E12282J2
Switch-out
Regen resonator compartment Diagnostics compartment
Pump module
Figure 2.2-2Photograph of a diode-pumped regenerative amplifier (DPR).
Table 2.2-1: Performance requirements of principle oscillators.
Main, SSD, and backlighter oscillators Fiducial oscillator
Seed pulse cw mode-locked master oscillator
Oscillator type Regen Regen
Input energy ~100 pJ/ns ~100 pJ/ns
Output energy (single pulse) ~1 mJ ~1 mJ
Amplitude stability ≤2% ≤2%
Pulse duration 0.1 to 4 ns 4.8 ns comb
Temporal jitter ≤30 ps ≤30 ps
Pointing stability ≤10 nrad ≤10 nrad
Energy contrast >100,000:1 >100,000:1
OMEGA System Operations Manual — Volume IPage 20 of 37 — Revision A
G7384J1
Pocket cell tower
Main IRS pickoff
Pointing
MRE
SSD
reg
en
Main regen
PreIR3
60
132
Centering
SSDpickoff
Figure 2.2-3The main and SSD diode-pumped regenerator amplifiers are located on the same optical table in PGR.
Figure 2.2-4A three-dimensional view of the PGR optical tables containing the main, SSD, and backlighter diode-pumped regenerators, the SSD modulators, and the periscope that delivers the beams to the driver-line area in the Laser Bay. The tables also contain diagnostic equipment and various optics used to point, center and collimate the beams. The 2-D SSD modulator is located inside the x-band box.
Smoothing by spectral dispersion modulators
SSD regen
Main regenBacklighter
regen
Periscope
IR spectrometer
G7364J1
Chapter 2: Drivers July 2007 — Page 21 of 37
Figure 2.3-1Block diagram of the smoothing by spectral dispersion system with hardware timing system triggers. Faraday rotators (FR’s) provide optical isolation to prevent any signal system back-reflection.
2.3 Smoothing by Spectral Dispersion (SSD)
Smoothingbyspectraldispersion(SSD)isatechniquethatimprovesbeamuniformityatthetargetbyimposingatime-varyingwavelengthshiftonthedriverpulse.TheSSDdriveristhedesignationappliedtothetrainoflaser-driverelementsthatcanprovidepulseswiththesmoothingeffect.TheSSDdriverlineisfullyoutfittedfortwo-dimensional(2-D)SSDoperation(refertoFig.2.3-1,below).Themain,backlighter,andfiducialdriversdonothaveSSDcapability.
Smoothing by spectral dispersion is implemented onOMEGA to achieve high-irradiationuniformityondirect-driveinertialconfinementfusiontargets.Beamsmoothingmustoccurbeforethetargetcansignificantlyrespondtothelasernonuniformity.TwofactorsdeterminethelevelofuniformitythatcanbeachievedwithSSD:bandwidthandspectraldispersion.Theamountofbandwidthdeterminestherateofsmoothing,andtheamountofspectraldispersiondetermines themaximumreductioninnonuniformitythatcanbeachieved,aswellasthelongestspatialwavelengthofnonuniformitythatcanbesmoothed.
Whencombinedwithpolarizationbeamsmoothingusingdistributedpolarizationrotators(DPR’s)andmultiplebeamoverlap,the1-THz,2-DSSDsystem(1.5#11Å)availableonOMEGAproducesalargenumberofindependentspecklepatternsandachievesasymptoticnonuniformityintherangeof1%–2%withasmoothingtimeof~500ps.
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3.3 GHz~1.5 Å/pass
10.4 GHz11 Å/pass
OMEGAG4
gratingpair
LARA
G1/G2gratingFR
Fromregen
M1 phasemodulator
Imagerotation
G3grating FR XM2 phase
modulator
5 Hz
5 Hz
1st SSD dimension
2nd SSD dimension
Hardwaretiming system
OMEGA System Operations Manual — Volume IPage 22 of 37 — Revision A
(a)The System Description document, S-AA-M-012, Chap. 5, and Sec. 5.9 contains a description of the distributed phase plate.
Bandwidthandspectraldispersionarebothconstrainedby the frequency-tripled,glass-laserconfigurationusedinOMEGA.High-efficiencyfrequencytriplingoflaserlightwithasingletriplingcrystallimitsthebandwidthto~5Å(FWHM)intheinfrared,butadual-crystaltriplingschemeincreasesthisto~14.5Å(FWHM).Spatial-filterpinholesinthelaserchainalsolimitthespectralspreadofthebeamtofourtoninetimesthebeam’sinfrared-diffractionlimit.Evenwiththeseconstraints,thelevelsofuniformityrequiredforOMEGAexperimentscanbeachievedusingSSD.
Thefocusofahigh-energylaserbeam,suchasOMEGA,containssignificantnonuniformity,asshowninFig.2.3-2(a).Aspecklepatternproducedbyaphaseplate(a)ischaracterizedbyasmooth,well-definedintensityenvelopeontarget.Thespeckleisahighlymodulatedintensitystructureproducedbyinterferencebetweenlightthathaspassedthroughdifferentportionsofthephaseplate.SSDsmoothesthisspecklestructureintimebyprogressingthroughasequenceofmanycopiesofthisspecklepattern,eachshiftedinspace,sothatthepeaksofsomefillinthevalleysoftheothersatdifferenttimes.Whenaveragedintime,thiseffectisqualitativelysimilartowhole-beamdeflection,asshowninFig.2.3-2(b).
G7385J1
Frequency-tripled beam
(a) (b)
2-D SSD
Figure 2.3-2(a) An infrared beam that is amplified and frequency tripled to the ultraviolet has irregular uniformity at its focus. (b) Two-dimensional smoothing by spectral dispersion introduces high spatial-frequency speckle with a distributed phase plate (DPP) that is rapidly shifted at focus in two orthogonal directions to produce a more-uniform-intensity beam.
TheseshiftedspecklepatternsaregeneratedbytwokeySSDcomponents.Thebeamispassedthroughanelectro-opticphasemodulator,whichimposesarangeoffrequencies(bandwidth)uponthelaserlight.Thebandwidthisthenspectrallydispersedbymeansofdiffractiongratings.InOMEGA,twomodulatorsofdifferentfrequenciesareusedwithdiffractiongratingsorientedsuchthateachbandwidthisdispersedinaperpendiculardirection(seeFig.2.3-3).Becauseofthedispersion,eachspectralcomponentfocusesontothetargetinaslightlydifferentposition,producingtherequiredshiftedspecklepatternsthatchangeintime.
ForOMEGA,implementinglargebandwidthsanddivergenceinthesecondSSDdimensionisadvantageousbecausethebandwidthfromthesecondmodulatorisnotdisperseduntilafterthemostlimiting spatial-filter pinhole,which is located in theLARA in thedriver-line area.The constraintresultsfromaspatial-filteringrequirementassociatedwiththeserratedapertureapodizerusedtosettheOMEGAbeamprofile.AslottedLARAspatial-filterpinholewithitslongaxisalignedalongthedirectionofdispersedbandwidthfromthefirstSSDdimensionisemployedtomaximizespatialfilteringofthebeam.
Chapter 2: Drivers July 2007 — Page 23 of 37
2.4 Large-Aperture Ring Amplifier (LARA)
TheopticallayoutoftheamplifiersandtheotherdriverequipmentlocatedintheLaserBayisshowninFig.2.4-1.Themostimportantamplifiersare40-mmLARA’s.Oneisprovidedforeachofthemain,SSD,andbacklighterpulses.Eachamplifierprovidesatypicalgainof12,000inatotaloffourroundtrips,therebyproducinga0.6-Joutputpulse.
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Ein(t) Eout(t)
3.3 Ghz
Skew inx-direction
Disperse ox in x-direction; unskew
in x-direction
Skew in y-direction; disperse ox
in y-direction
Disperse oy in y-direction; undisperse ox in in y-direction
ox
10.4 Ghz
oy
Figure 2.3-3The basic 2-D SSD implementation uses two modulators and four gratings.
G3654bJ1
Backlighter LARA
64 mm
To A split
ASPPeriscope to A split
Periscopefrom PGR
Main LARA
SSD LARA
Spatial�lter
Kinematic mirrorFaraday rotator
40 mm
40 mm
40 mm
Figure 2.4-1The driver line has three LARA-s and a 64-mm amplifier. The beams enter the driver line at the periscope from PGR.
OMEGA System Operations Manual — Volume IPage 24 of 37 — Revision A
OMEGAusesfour-passLARA’stoprovidethebulkofthegainneededtoboosttheregenoutputtothe~5-JlevelrequiredforinjectionintothemainOMEGAamplifierchain.Thisrepresentsadeparturefromthetraditionallinearamplifierchainsandwaschosenforitscompactness,excellentperformancecharacteristics,andrelativeeaseofmaintenance.Thisamplifiercanprovidehigh-gainandhigh-qualitybeamsforpulsesinthe0.1-to5.0-nsrange.AschematicoftheopticallayoutfortheLARAisshowninFig.2.4-2.
E6591J2
Four-lens spatial �lter
Input
Apodizer
Output
Pockelscell
5 ft × 10 ft table
Alignmentdiagnostic
40-mm amp
Figure 2.4-2The LARA used in the OMEGA laser driver. The Pockels cell admits the input pulse and then, after four round trips, switches the amplified pulse out. The four-lens spatial filter is used in defining the alignment axis.
TheLARAisatypeofregenerativeamplifierthatusesarelativelylarge(40-mm)rodamplifier,an imagingspatialfilter,andanelectro-optical switch,allcontained inanoptical ring.Pulsespassthroughtheinputapodizerandareinjectedintothering.Theradialtransmissionoftheapodizerisspeciallydesignedtocompensatetheradialgainvariationinthe40-mmamplifierrod.Thepulsesthenmakefourroundtrips,andareswitchedout.Duringeachroundtripthepulseisamplifiedbyafactorof~10.5.Thisgainvalueisveryconservativesincethe40-mmamplifieriscapableofprovidinggainsof15to20pertrip.Thisconservatismhelpsimprovethereliabilityoftheamplifierandprovidesamplereservegainforfutureneeds.
CentraltotheperformanceoftheLARAisthefour-lensspatialfilterthatprovidesimagerelayingsuch thatany locationwithin thering ismappedonto itselfonsubsequentroundtrips.Thisfeatureaffordstheabilitytoaccuratelyaligntheringandensurethattheopticalpathisreproducible,therebyallowingcontrolofbeamqualityathighgain.Theround-trippathlengthisapproximatelyfourtimestheeffectivefocallengthofeachlenspair.
Thespatial-filterpinholeismountedtoaprealignedpositionthatservesasapointingreferencefor alignment of the ring.Themount is kinematic so that the pinhole canbe removedduringfinealignmentandaccuratelyreplaced.TheinternalalignmentoftheLARA’scanbepreciselymaintained
Chapter 2: Drivers July 2007 — Page 25 of 37
byaligninganintra-ringcrosshairtoitselfandbyaligningthebeamtothespatial-filterpinholeusingmirrorswithinthering.Thepulsedregeninputbeamistheninjectedintotheringandalignedtothesereferencesusingexternalmirrors.
Theinjectionandrejection(inputandoutput)ofpulsesareperformedusingaPockelscellandtwopolarizingbeamsplitters.ThePockelscellisdrivenbyathyratron-basedswitchingcircuitfeedingachargeline;aswitchingtimeofmuchlessthanthecavityround-triptime(22ns)isachieved.Thesystemusesa66-nschargelinetoproducefourpassesthroughtheamplifier.
IfthePockelscellispassive,thepulsepassesthroughtheringexactlyonetime.Ifahalf-wavevoltageisappliedtothePockelscellbeforetheopticalpulsehasfinisheditsfirstroundtrip,thePockelscellcompensatesforthehalf-waveplateandthelaserpulsewillcontinuetravelaroundthering.Opticalamplificationwillcontinueaslongasthevoltageisapplied.Afterthehalf-wavevoltageisswitchedoff,theamplifiedlaserpulseisejectedoutofthering.TheIRcontrastspecificationofthePockelscellismaintainedtowithin3.4#104bycarefulalignmentofthePockelscellandthehalf-waveplate.
ThegainperformanceoftheLARAversusthecapacitor-bankenergyisshowninFig.2.4-3.Totalgainsofgreaterthan40,000havebeenobtainedwithnoappreciabledegradationinbeamquality.
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103
104
105
Bank energy (kJ)
20 25 30 35 40 45 50
Gai
n
4.0 kV
4.5 kV
5.0 kV
5.5 kV5.2 kV
5.7 kV
Figure 2.4-3The total gain of the LARA system as a function of capacitor-bank energy. Gains of greater than 10,000 are easily achieved with four passes through the ring.
TheselectionofthemainortheSSDdriverasthesourcefortheOMEGAbeamsismadebyusingakinematicmirrorthatreflectstheoutputofthemaindriverintothe64-mmlaseramplifier.ThemirrorcanberemovedtoallowtheSSDpulsetoenterthe64-mmlaseramplifierdirectly.Theselectedbeamisamplifiedto~4Jbythe64-mm,single-passamplifier,whichisthelastdriver-lineamplifier.ApermanentmagnetFaradayrotatorandliquidcrystalpolarizer(circular)isolatethedriverfromanysystemback-reflection,islocateddirectlyafterthefinal64-mmamplifier.Thedriver-lineoutputsarespatiallyfilteredandinjectedintothefirstbeamsplitter(stage-A),wherethedriver-linepulseispropagatedintotheOMEGApoweramplifiers.
ThebacklighterLARAproducesa1.4-JoutputandgoesthroughonespatialfilterandFaradayisolator.Thisenergyisappropriatefordrivingoneofthethreestage-Alegs.
OMEGA System Operations Manual — Volume IPage 26 of 37 — Revision A
2.5 Fiducial Subsystem
Thefiducialdriverlineislocatedonthenorthendmirrorstructureinthetargetbay.Thefiducialdriverlineusesaseriesofamplifierstoprovidethreefiducialwavelengths.TheseareanOMEGAdiode-pumpedregenerativeamplifier(ODR),liketheunitsinthePGR,andahigher-powered“ODR+,”whichreplacesthetraditionalLARA.
Infrared, visible, andultraviolet timing-fiducial signals are needed tomatch thewavelengthsensitivityofvariousdiagnostics.Thefiducial-amplifiersubsystemprovidesacompact,all-solid-state,diode-pumped,laserfiducialsystemthatsatisfiesallOMEGArequirements.
TheOMEGAfiduciallasersystemmustproducea3.5-nscombof200-psfull-widthathalf-maximum(FWHM)opticalpulsesseparatedby0.5nsatIR,green,andUVwavelengths(seeFig.2.1-7).AnNd:YLFlasersystemwithsecond-andfourth-harmonicgeneratorsisusedtoproduceIR,green,andUVfiducialsignals.Theamplitudevariationofeachpulseinthecombmustnotexceed50%ofthemaximum.TherequiredIR/greencombenergyis1mJ.Themostcriticalrequirementsforthefiducialsystemare10-mJenergyatUV(4~)fiducialandastabletimedelay(~165ns)betweentheIR/greenandUVfiducials.
TherelativelylongdelaybetweenUVandIR/greenfiducialsisdictatedbythephysicallocationofvariousOMEGAdiagnostics.SinceIR/greenfiducialsmustbegenerated~165nsbefore theUVcomb,a165-nsdelaylineisrequiredbetweentheIR/greenandUVfiduciallauncherstoprovidethesimultaneousarrivalofthefiducialstoallOMEGAdiagnostics.
Thefiducialsystemprovidesanopticaltimestamptoidentifyandmeasureinformationaboutthetimingandshapeofthelaserpulsedeliveredtothetarget,alongwiththeeventsrecordedbyvariousstreakcameras.ThesignalsprovidedbyUVandx-raystreakcamerasprovideimportantinformationaboutthetime-dependenttargetdevelopmentunderilluminationbyshapedlaserpulses,andisveryimportantforcorrectandunambiguousinterpretationofthedatageneratedfromashot.Figure2.5-1showshowafiducialcombcanbeusedtolocateactivityintimeduringashotusingavisualstreakcamera.
G7388J1
Figure 2.5-1Raw data from the IR3 streak camera in PGR illustrates that the eight fiducial pickets can be used to synchronize the activity in the system.
Chapter 2: Drivers July 2007 — Page 27 of 37
AblockdiagramofthesystemisshowninFig.2.5-2.ThesystemisseededbytheshapedcombproducedbytheIFES.Thefiducialisuniqueinthattheoutputofits10-Vpulsegeneratorprovidesatime-basereferencefortheentireACSLsystem.Thispulseisusedtotriggerthehigh-speedsamplingscopethatdiagnosespulseshapesproducedbythesystem.AnNd:YLFOMEGAdiode-pumpedregenerative(ODR)amplifierbooststhecombenergyfromtensofpicojoulesto~4mJ.ThemainportionofthissignalisusedasanIRfiducialandforgeneratingagreenfiducialviaasecond-harmonicgenerator(SHG).
2.5.1 ODR and ODR+
ThefiducialODRispumpedwithone150-Wfiber-coupleddiodearray.TheODRoutputenergyis>13mJatthemaximumpumpenergy(seeFig.2.5-3).Withthisinput,theamplifierproduces~50mJofIR,meetingtheenergyrequirement.
AportionoftheODRoutputisusedtoseedthesecondregenerativeamplifier,designatedODR+.ThehigherpowerODR+isaddedtoproducetheadditionalgainrequiredtoachievetheUVenergyspecification.Atthesametime,itprovidestherequired165-nsdelaywithasmallfootprintandwithoutbeamdegradation. Second-harmonic generation (SHG) and fourth-harmonic generation (FHG) arerealizedwithbeta-bariumborate(BBO)crystals.
E13763J2
IFES FHG
SHG
IR �ducial
Green �ducial
UV �ducial
Delay line and gain
ODR+ODRFigure 2.5-2A block diagram of the OMEGA fiducial-laser subsystem.
100
5
10
15150 W50 W
13.5 mJ
4.1 mJ
20 30 40 50 60
OD
R+
out
put e
nerg
y (m
J)
Pump driver current (A)E13769J2
Figure 2.5-3ODR+ is able to produce sufficient energy for effective double-pass amplifier energy extraction.
OMEGA System Operations Manual — Volume IPage 28 of 37 — Revision A
2.5.2 Fiducial Frequency Conversion
Figure2.5-4showsablockdiagramofthefrequencyconversionsetup.Beta-bariumboratecrystals(BBO)areutilizedforfrequencyconversiontothefourthharmonic.An11-mm-longtype-Icrystalisemployedforsecond-harmonicgeneration(SHG),followedbya6-mm-longtype-Icrystalforfourth-harmonicgeneration(FHG).Afused-silicaprismisusedtospatiallyseparatetheUVfiducialbeam,andatelescopematchesthebeamsizetoefficientlylaunchtheUVpulsesintoamultimodefiberbundle.
WiththeIRbeamresizedforefficientFHG,theenergyrequirementhasbeenmet.Thefiducialcomb(a)inFig.2.5-5injectedintotheODRhasbeenprecompensatedsuchthatboththe(b)greenand(c)UVfiducialsmeetamplituderequirement.
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plitu
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(a) (b) (c)
Figure 2.5-5The ODR injection fiducial comb (a) is precompensated such that the (b) green and (c) UV fiducials satisfy the requirements.
Figure 2.5-4A block diagram of UV frequency-conversion setup and fiber bundle launching.
2.5.3 Fiducial Delivery
High-UVfiducialenergyisrequiredbecauseofthelow-UVsensitivityofthex-raystreakcameraphotocathodesemployedinOMEGAtargetdiagnostics.Frequency-conversionefficienciesof50%to75%forbothsecond-andfourth-harmonicgenerationhavebeendemonstrated;therefore,therequiredIRenergyis~10mJ.
Chapter 2: Drivers July 2007 — Page 29 of 37
AUVmultimode-fiberdeliverysystemisusedtocouplefiducialcombsintothediagnostics.OMEGAneedsupto19channelsofUVfiducial;therefore,a19-fiberbundleisusedtolaunchtheUVcombintothedeliveryfibers.Toprovideequalenergydistributionandmisalignmentinsensitivityforthefiber-bundlelauncher,aUVfiducialbeammustsignificantlyoverlapthe19-fiberbundle,bringingthetotalUV-combenergyrequiredto10mJ.Toavoidopticaldamageoftheactiveelement,thefluenceiskeptbelow5J/cm2,andthedeliveryfiberisre-imagedintoanactiveelementwith2#magnification.
2.6 Hardware Timing System
TheHardwareTimingSystem(HTS)providesprecision-timingsignals that synchronize thesubsystemsoftheOMEGAandOMEGAEPLaserSystemstoproducealaserpulseandacquirediagnosticdata.End-to-endsynchronizationisprovidedbythereferencefrequency(RF)sourcethatdrivesthelaser’smasteroscillator,theMasterTimingGenerator(MTG),andthetimingcrates.TheMTGprovidesderivedratesthatarealsodistributed.Localtimingstations,knownas“crates,”includeprogrammablemodulesthatprovidesynchronized,preciselydelayedrateandtriggersignals.
Thesignalsaredistributed throughout the facilityandprovided toequipmentviaco-locatedComputerAutomatedMeasurementandControl(CAMAC)timingcrates.Asoftwarecontrolinterfaceisprovidedtoallowoperatorstoselectratesandsetdelaystothesetimingsignals.AblockdiagramofthissystemisshowninFig.2.6-1.
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Reference frequencygenerator(38 MHz)
Master timing generator Power conditioningcomputer
Master oscillator
Pulse generation and pulse shaping
(5 Hz)
Powerampli�ers
Laser diagnostics
Target
Target diagnosticsRate regenerator
Timing crate
Synchronizedprecision-delayed
triggers
Ampli�er powerconditioning
Delay moduleDelay module
Delay module
Synchronized rates and triggers
Typical of OMEGA installations
Triggerampli�er
Figure 2.6-1Block diagram of the Hardware Timing System used in OMEGA. All signal rates are synchronized to the 38-MHz reference frequency.
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TheMTGislocatedintheDriverElectronicsRoom(DER).Thisunitacceptsamaster-timingreferencefrequencysignal(nominally38MHz)fromthereferencefrequencygenerator(RFG),whichislocatedinthedriverstestbed(formallytheoscillatorroom).Thetimingsystemisreferencedtothe38-MHzreferencefrequencysignal.Variousslowerratesaregeneratedanddistributedbythissystem.TheMTGalsoacceptstwoseparate,hard-wiredasynchronous“enable”signalsfromthepower-conditioninghostworkstationtocontroltheshotsequence.Theshotsequencecoordinatesthefiringofthelaser,whichincludestheselectionofaseedpulsefromtheIFESshaped-pulsetrainintheregen,firingtheamplifiersinthedriver-lineareaandinjectingthelaserpulseintotheOMEGALaserSystem.SeeHardwareTimingSystemDefinitionDocument(S-SH-M-001)formoredetails.
TheMTGsendsoutsynchronizedperiodictimingsignalstoassociateddigital“fan-out”units.Thefan-outunitsfeedsignalstomodulartimingunits,called“timingcrates.”Therearefan-outunitsforhorizontalandverticalvideosynchronizationandalllogicleveloutputs.
Themodulartimingcratesarelocatedneartheequipmenttheycontrolandprovideapreciselydelayedsynchronousoutputsignaloftheappropriatevoltageandduration.Thesynchronizationratesourceissoftwareselectableandisbasedonthemaster-timing-assemblyoutputs.Theoutputsignalisdelayedtotheinputsignalbyaprogrammablevaluedeterminedbytheuser.
2.7 Laser-Driver Diagnostics
Thedriver-linediagnosticsmaybedividedintofivemaincategories
• Pulse-energy• Pulse-shape• Timing• Spectrum(wavelengthand/orbandwidth)• Pointingandcentering
Most diagnostics produce signals at the 5-Hz pulse-repetition rate, except the IR streak cameras, which run at a 0.1-Hz pulse rate. Key diagnostics also acquire and log the characteristics of the particular pulse that is amplified in the LARA’s and power amplifiers.
Diagnostic data is monitored continuously between shots and may be stored in the database on demand. On-the-shot data acquisition logs the diagnostic data with all the other shot information in the database. Data acquired in either way can be displayed on the driver console in the OMEGA Control Room and is also available for display on workstations located in the PGR and the DER. The following measurement systems are used:
• IntegratedFront-EndSource(IFES)monitoring• Regenerativeamplifier(regen)characteristics• SSD,laser-bandwidthbroadening• LARAcharacterization
The IFES diagnostics are illustrated in Fig. 2.7-1. ThediagnosticslistedinTable2.7-1areprovidedinthelaserdrivers.
Chapter 2: Drivers July 2007 — Page 31 of 37
2.7.1 Laser-Energy Measurements
Energymeasurementsaremadeatseveralpointsalongthelaserdriversusingphotodiodesthatcanviewasampleofthebeamregardlessofthesystemconfiguration.Thesediodesarecalibratedagainstalaser-probeenergymeterinthePGRandcalorimetersinthedriverlinethataretemporarilyinsertedinthedirectbeam.
Single-pulsephotodiodesignalsaresenttoCAMAC-gatedintegratorsforcomputeracquisition.CharacteristicsofregensintheDERandPGRarediagnosedbysendingthephotodiodesignalsthroughbandpassfilterstomultichanneldigitaloscilloscopes.TheoscilloscoperecordsareacquiredthroughaGPIBinterfaceandanalyzedbytheacquisitiondevicemanager(ADM)softwareapplicationtoprovidepeakamplitude,FWHM,andtimeofpeakamplitude.SeeFig.2.7-2foranexampleofatypicalADMGUI.
Theproperfunctioningofeachunitisverifiedonacontinuousbasis.Theenergymeasurementsaremadeclosetothe5-Hzcyclerateofthesystem,andreal-timerunningstatisticsarecomputedfromthisdatastream.
2.7.2 Pulse-Shape Measurements
Roughpulse-shapemeasurementsaremadeusingsingle-modefibersconnectedtofastdiodesmounteddirectlyattheinputofaTektronixTDS8000Seriesoscilloscope.Thefiberssamplethesingle
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MOwavelength
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Injection
IFA energy
DAMs RegenIFES
�ber amp
Figure 2.7-1Block diagram of the IFES diagnostics. The signal generation runs from left to right.
Table 2.7-1: Laser-drivers diagnostics.
Diagnostic Location Main SSD Backlighter Fiducial
System timing PGR X X X X
Wavelength monitoring DER X X X X
Spatial beam profiles PGR and DLA X X X
Laser spectrum PGR X
Pockels-cell timing jitter PGR and TB X X X X
Laser energy PG, DLA, and TB X X X X
Pulse shape PGR X X X X
IR streak timing PGR X X X X
Prepulse contrast DLA X X
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pulsesselectedfromeachofthethreePGRregenpulsetrainsthatseedtheOMEGAdriverlines.Thedynamicrangeoftheseoscilloscopetracesallowverificationofthepulseshapesinjectedintothedriverlines,but isnot sufficient fordetailedanalysisor inputRAINBOW simulations.For thatpurpose,amultichannelstreakcamerawasinstalledinthePGR.
TheIRstreakcamerasinPGRareusedtomonitortherelativetimingandpulseshapesfromthefourregens.Eachstreakcamerahasfive-channelfiberinputstoaccomplishthis.Eachinputisimagedontoastreaktubeviaanall-reflectiveopticalsystem.Thephotocathodeisdedicatedtothefourregensinthefollowingproportions:40%main,20%SSD,20%backlighter,10%fiducial,and10%interchannelgap.Thisarrangementcanbeeasilyreconfigured.Theoutputofthestreaktubeiscoupledtoa515#512CCDarraythrougha2:1fiber-opticreducingbundle.Thestreakrampsaresynchronizedtothelaserbya0.1-HzpulseratefromtheHardwareTimingSystem.Thisguaranteesthecaptureofonepulseevery10s.Inaddition,thecameracanbesynchronizedviasoftwaretocapturedataontheshot.
Forcalibrationpurposesthecamerahasaself-containedflatfieldingsystemandadedicatedmultichannelfiducialmodeforrapidsweepcalibration.AlocalPCcontrolsthestreakcameraandCCDcamera.Customsoftwareisusedtocoordinateallacquisition,calibration,anddatamanagement.
2.7.3 Pulse-Timing Verification and Pockels Cell Timing Jitter
Pockelscellsareusedthroughoutthelaserdriverstofacilitatetheoperationofthesystem.ThevariationinthetimedelaybetweentheoriginationofthePockels-celltriggersignalandthetimewhenthefullelectricfieldappearsacrossthecellisakeyparameterthataffectsthepulse-to-pulseuniformityofthelaser-driveroutput.Thesetimingvariations,called“jitter,”areoftheorderof~1ns.
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Figure 2.7-2Screen shot of the SSD driver ADM graphic user interface. Readings that are out of tolerance are shown in red.
Chapter 2: Drivers July 2007 — Page 33 of 37
Pulse-timingandtiming-jittermeasurementsofvariousPockelscellsintheOMEGALaserSystemarecarriedoutbyusingCAMAC-based,high-speed,time-to-digitalconverters(TDC’s).TheTDC’suseseparateelectrical-inputtriggerstostartandstoptheinternalcounters.Thestart-countingtriggerisderivedfromthemastertimingfan-out,andthestop-countingtriggerisgeneratedbytheelectronicsthatdrivetheelectricfieldonthePockelscell.ThenumberofcountswithintheTDCisreadout,andthedataareuploadedtothehostcomputerforanalysis.Real-timerunningstatisticsarecomputedfromthisdatastreamandusedtomonitor theoperationalstatusof thesystem.Thissystemcontinuouslyverifiestheproperfiringsequenceofapproximatelytwodozendevices,withnanosecondaccuracyingeneralandwith50-psaccuracyinsomeselectedcases.ThisisparticularlyimportantforthePockelscellsinthesystembecausethemistimedfiringofanyoneofthemleadtotheincorrectfiringofthefullOMEGAsystem.
Pulse-timingverificationhas turnedout tobeof increasingimportancesincedifferentpulseshapesarebeingpropagatedthroughthelasersystem.ForthatpurposethesinglepulsesfromanyofthePGRregensinjectedintotheOMEGAdriverlinesarecheckedforpropertimingattheregenoutput.PhotodiodesattheselocationsfeedappropriateTDCchannelsforcontinuoussurveillance.
2.7.4 Spectral Bandwidth and Central Wavelength from SSD
InIFES,thecorrectcentralwavelengthandamountofbandwidthbroadeningofthelaserafterSSDare important for high-efficiency, third-harmonic conversion at the endof theOMEGALaserSystem.AWavemasterlaserwavelengthmeterlocatedintheDERallowsmeasurementofthecenterwavelengthto±0.02Å.
InthePGR,thedetectorcoupledtothespectrometeroutputfollowingSSDmodulationisaslow-scan,cryogenicallycooled,charged-coupled-device(CCD)arraywith18bitsofdynamicrange.Thelowquantumefficiencyofthedetectorat1nmisovercomebyefficientlycouplingthelightintothespectrometer(i.e.,matchingnumericalapertures)andbysamplingahighpercentage(4%)ofthelaser-beamenergy.Theoutputofthearrayisbufferedbyanintermediatelocalcontrollerandthenpassedalongtotheexecutivecomputer.ThesameinterferometeralsoallowstheSSDbandwidthandtheassociatedmodulationparameterofeitherSSDmodulatortobemeasured,aslongasthereisnowavelengthdispersion.
Tomeasure the combinedbandwidth of bothSSDmodulators, includingdispersion, the IRFabry–Perotspectrometersystemarebeingcharacterized(seeFig.2.7-3).Inthiscase,thelaserbeamtobediagnosedentersanintegratingsphere,theoutputofwhichisthesourcefortheinterferometer.Thissystemisindependentofwavelengthdispersionandisabletomeasurethebandwidthto±0.02ÅintheIRandyieldanestimateofthemodulationparametertobetterthan2%.
2.7.5 Pointing and Centering Diagnostics
CCDimagingdevicesareusedthroughoutthelasersystemasalignmentaids,asbeamprofilediagnostics,andforvariousotherapplications.Sincetheseareusedforpreshotalignment,theimagesarenotincorporatedintotheshotdatabase.SeeTable2.7-2foralistofdriver-imagingdiagnostics.
The 5-Hz output of the regen is propagated through the optical train that is to be aligned and imaged on a video camera. In the laser drivers, separate cameras are provided for pointing and centering except at the DL-ASP at the end of the driver-line train. As a result, the DL-ASP (which is the same design
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Figure 2.7-3Infrared spectrometer images showing bandwidth of both SSD modulators, including dispersion.
Table 2.7-2: Driver imaging diagnostic cameras.
Camera Beam Location
Crystal centering Main, SSD, and backlighter PGR
Crystal pointing Main, SSD, and backlighter PGR
Regen and centering Main and SSD PGR
Regen pointing Main and SSD PGR
BL regen centering Backlighter PGR
BL regen pointing Backlighter PGR
Output centering Main, SSD, and backlighter PGR
Output pointing Main, SSD, and backligh-ter PGR
Main LARA centering Main Driver line
Main LARA pointing Main Driver line
SSD LARA centering SSD Driver line
SSD LARA pointing SSD Driver line
BL LARA centering Backlighter Driver line
BL LARA pointing Backlighter Driver line
Driver line ASP Main and SSD Driver line
Fiducial regen centering Fiducial Target Bay
Fiducial regen pointing Fiducial Target Bay
Fiducial LARA centering Fiducial Target Bay
Fiducial LARA pointing Fiducial Target Bay
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as the A- and C-ASP’s) is the only place in the laser drivers where it is necessary to change the optical configuration to get both pointing and centering data. The ASP’s are equipped with optical elements on two movable stages controlled by two-state device-control modules, which receive commands from the executive via a LON. The stages can be positioned to provide coarse pointing, fine pointing, or centering images to a single camera that is part of the ASP.
The cameras are controlled by one of three Sun workstations located in the PGR, DLA, and Fiducial, which contain two frame grabbers each. Commands to the cameras originate from the OMEGA imaging GUI (OIGUI). The image that the frame grabber acquires and digitizes is analyzed locally in the image server.
In general, the image processing gives the X and Y locations, in pixels, of the center of a spot, a crosshair, or a reticle to the camera detector array. Other parameters, such as lineouts or X and Y from an input set of pixel coordinates are provided by some of the algorithms.
The executive can command the image-analysis computer to perform the appropriate processing and return the results over the network. The results are also impressed on a video image that is output to an RF modulator and is available on the video distribution system for display to the operator.
The image-analysis results are interpreted as a deviation from the reference crosshairs by the operator or by alignment processing in the executive. If an adjustment of the optical train is necessary, commands are passed from the executive to the appropriate dual-axis control module(s) via a LON. Pointing and centering alignment generally involves commands to two dual-axis control modules (DACM’s), one that positions a pointing mirror and one that positions a centering mirror. The pinholes in spatial filters are positioned by a single DACM.
Note that these alignment “control loops” are closed step-wise (measure, compute, move, measure) over a period of from 10 s to ~1 min; these are not real-time loops.
2.8 Laser-Driver Controls
Thelaser-driverssubsystemhasarelativelysmallnumberofuniquecontrolandsensingelementsin comparison to thealignment andpower conditioning subsystems,whichhavea largenumberofidenticalelementstoserveparallelbeamlines.Alsothelaserdriverswillalwaysbemoredevelopmentalinnatureandwillalwaysrequireahighlevelofinvolvementbytheoperators.Thesefactors,combinedwiththefactthatthelaser-driversequipmentisinfourseparatelocations,ledtoaconfigurationthatprovidescontrolsystemsinfourlocations(theDER,thePGR,thedriver-linearea,andthefiducialareaintheTargetBay,inadditiontotheControlRoom)andpermitsoperationsinsupportofsystemshotsfromeitherthePGRortheControlRoom.
2.8.1 Configuration
DrivercontrolsconsistofseveralSunworkstationsandPC-compatiblecomputerstooperateandmonitorcriticaloperatingparameters,diagnostics,andapplicationswithinthedriverssubsystem.Thesecomputersconnecttoperipheralequipmentbymeansofthegeneral-purposeinterfacebus(GPIB),localoperatingnetwork(LON),ordirectlyviaserialports.Figure2.8-1(driverscontrols)isablockdiagramofthelaser-driverscomputercontrols.Thisconfigurationprovidescontrolanddataacquisitionforthe
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Sun
PC
Other
Birch (CR) - LDT station
Beet (DER) - AWG pulse-shape system testing
Ecleto (DER) - Pulse shaping - PC anywhere
Sycamore (CR)
- Laser drivers executive - dvcgui - adm gui - drvtool - balign - oigui - syscal - Netscape - repdisp
Serial VideoDEMOD
Whitewright (CR) - LDT work station
Bart-OMG (LaCave) - BW reduction - A-near�eld - UV streak camera - PC anywhere
HP In�nium 1 (PGR) - PGR timing - Driver timing - PC anywhere
Sachse 1 (PGR) - IR1 - PC anywhere
Coconut (LaCave) - AITED - CTD
Serial
RIM (DER)
Welch (PGR) - Remote control of applications - PC anywhere
Ratcliff (DER) - Pulse shape analysis
Aspen (DER) - HTSS - Imaging - ADM
HTS: DER(A), DER(B), DER(C)
GPI
B
GPI
B
GPI
B
LO
N
LO
N
Desoto (PGR) - OMEGA pulse shape measurements - IR3 - PC anywhere
Eldorado (PGR) - PGR spatial pro�le CCD camera
Ossena (PGR) - Display
Baobab (LB) - Contrast - Tung terminal
Tung (LB) - HTS - Imaging - ADM
Saginaw (DLA) - Back-up IR pre-pulse diagnostic
HTS: DLA
SerialSerial
VideoDEMOD
VideoMUX
Topol (PGR) - ADM LENA
- balign
Thorndale (PGR) - Pulse shape measurement and prediction
LON - DL
PGR anddriverline devices
Dogwood (TB) - HTSS - Imaging - ADM
LENA - balign
LON - FID
Fiducial devices HTS: Fiducial
Figure 2.8-1Block diagram of the laser-drivers controls that illustrates the elements of the control tree that is used for remotely controlled alignment throughout the OMEGA Laser System. The current OMEGA computer hierarchy is maintained in document C-FC-M-017.
Chapter 2: Drivers July 2007 — Page 37 of 37
alignmentoflaser-driveropticsfrominitialamplificationinthePGRthroughinjectionoftheamplifiedbeamintotherelaytothestage-Asplitter.ItalsoprovidesADMdataacquisitionforthedriverdiagnosticsandcontrolofthetiming-systemcrateinthedriverelectronicsroom(DER).Therodamplifiersinthedriver-lineareaarecontrolledbythepowerconditioningsubsystem.
EachcomputercommunicateswiththeLaserDriversExecutive,whichcontainsdevicecontrol,energydiagnostics,accesstoimaging,andvariousGUI’s.TheexecutivealsointeractswiththeShotExecutiveusingtheproprietaryOMEGAIntercommunicationProtocol(OIP)overethernet.
2.8.2 ACSL v2 Software
TheACSLv2softwareapplication isused tosetup,control,andmonitor thepulse-shapingprocess.Aserverisstartedforthesystemwhentheclientisfirstlaunched.PersonnelmayviewACSLv2inasecondlocationbyusingVFNsoftware.Allofthesettingsthatoperatorsneedareprovidedthroughtheclientinterface.
The information used to configure the system resides in three locations
• Oracledatabasetables• NationalInstrumentsMeasurementandAutomationExplorer• Registryentries
Under most circumstances, the user never needs to manipulate the information stored in these locations. Only ACSL system administrators should modify these settings. Administrative tools are provided through the server interface.
ACSL v2 has several advantages. The Oracle database schema has improved the efficiency, allowing shot settings to be restored accurately. The administrative and user settings are now separated. Instrument settings have been assigned security levels to partition data and restrict control. Universal channel delay is now available to change pertinent delays for an entire system at once. Arbitrary trigger timing can be used to “sync” multiple Tektronix 8000 scope channels for better reference.
The stripline (Shape) ID is not automatically sensed by ACSL v2. Information entered by the Operator during pulse shape setup is used to retrieve the pulse shape design and set-up data.
2.9 References
1. The System Description document, S-AA-M-012, Chapter 5, and Section 5.9 contains a description of the Distributed Phase Plate.