system operations manual volume i–system description ......35 2.8.2 acsl v2 software ..... 37 2.9...

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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.


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.


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.

G7362J1

0.00.0

0.2

0.4

0.6

0.8

1.0

0.5 1.0 1.5

Time (ns)

Nor

mal

ized

pow

er

2.0 2.5 3.0 3.5

IR output

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.


Figure2.1-2showsfourtypicalpulseshapesusedinOMEGA.TheappropriatestriplineassemblyisinsertedintotheIFESboxfortherequireddrivertoproduceapulsetrainattherateof300Hz,withthedesiredshapeandwidth.TheshapedoutputpulseisthensenttothePGRandinjectedintoregensforthefirststageofamplification.

G7363J1

Pow

er (

W)(

×10

11)

00.0 0.5 1.0

Time (s)(× 10–9)

1.5 2.0 2.5

2

4

6

8

Pow

er (

W)(

×10

11)

00 1

Time (s)(× 10–9)

2 3 4

2

4

6

8

Pow

er (

W)(

×10

11)

0.00 1 2 3 4 5 6

Time (s)(× 10–9)

0.5

1.0

1.5

2.0

2.5Po

wer

(W

)(×

1011

)

00.0 0.5 1.0 1.5 2.0 2.5 3.0

Time (s)(× 10–9)

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.


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


SSDILX lightwave


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


BacklighterILX lightwave


FiducialILX lightwave


FiducialILX lightwave


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.


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 shapedpulse 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.


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).


Manualcontrol

Isolator

PSPL 35 V

G7370J3

Diodelaser

Controlelectronics

Controlelectronics

Thermallystabilized


Isolator


ACSLscope

Diodelaser

Yb:�berFaraday

mirror with�lter


1030�lter WDM

90/10

Ecleto

Bias control

RS-232


DC1 DC2

E/O

Fiber


Wavelengthmeter

ModulatorColby 40

Trigger amp

Colby 40

Modi�edPSPL 10 V

Modi�ed PSPL10-V picket

To regens

MOD1gate-pulseinput


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.


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).

E8473J1

0.00.0

0.5

0.5

1.0

1.0

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Time (ns)

Measured 2~ output

Nor

mal

ized

pow

er

2.0 2.5 3.0 3.5 4.0 4.5

Design

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.


Manualcontrol

Isolator

PSPL 35 V

G7370J4

Diodelaser

Controlelectronics

Controlelectronics

Thermallystabilized


Isolator


ACSLscope

Diodelaser

Yb:�berFaraday

mirror with�lter


1030�lter WDM

90/10

Ecleto

Bias control

RS-232


DC1 DC2

E/ONEOS

Fiber


Wavelengthmeter

Modulator

Comb generator

Optical trombone

PSPL 10 V

To regens

MOD1gate-pulseinput


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.


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.


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.

G7377J1

Computer

RS-232-to-optical

Manualcontrol

Energymonitor

Biascontrol



Koherasmasteroscillator

IFES�berampli�erWavelengthmeter

PSPL 10 V PSPL 35 V

MOD1gatepulse

DC1 DC2

MOD2shapedpulse

Figure 2.1-10Block diagram of the dual-amplitude modulator.


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.


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.


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.


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.


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.


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


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


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.

E9086J1

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


(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.


2.4 Large-Aperture Ring Amplifier (LARA)

TheopticallayoutoftheamplifiersandtheotherdriverequipmentlocatedintheLaserBayisshowninFig.2.4-1.Themostimportantamplifiersare40-mmLARA’s.Oneisprovidedforeachofthemain,SSD,andbacklighterpulses.Eachamplifierprovidesatypicalgainof12,000inatotaloffourroundtrips,therebyproducinga0.6-Joutputpulse.

G7386J1

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.


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


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.

E7656J2

102

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.


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.


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.


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.

E13770J2

Pellin–Brocaprism

Telescope

Fiber bundle

FHG (BBO)

SHG (BBO)

m/2

E13774J2

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

am

plitu

de

0 2

Time (ns)

40 2

Time (ns)

40 2 3 51 3 51 3 51

Time (ns)

4

(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.


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.

G7389J1

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.


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.


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

G7390J1

CW MO

MOpower

MOwavelength

DAMenergy

Pulseshape

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


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.

G7391J1

Figure 2.7-2Screen shot of the SSD driver ADM graphic user interface. Readings that are out of tolerance are shown in red.


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


G7392J1

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


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


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.


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.

system operations manual volume i–system description ......35 2.8.2 acsl v2 software ..... 37 2.9...

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