Advancements in High Efficiency Semiconductor Lasers for ......2 LLNL-PRES-741702 –P. Leisher...

LLNL-PRES-741702This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC

AdvancementsinHighEfficiencySemiconductorLasersforHighPowerApplications

InstituteforEnergyEfficiencySeminarSeries

UniversityofCalifornia,SantaBarbara

PaulLeisherandBobDeri

November16,2017

2LLNL-PRES-741702 – P. Leisher – UCSB IEE Seminar – November 16, 2017

§ DiodelasersatLawrenceLivermoreNationalLaboratory

§ Powerscalingindiodelasers

§ Designforhighefficiencyandthermalmanagement

§ Othercausesofpowersaturation

§ Reliabilityconsiderations

§ Brightnessconsiderations

Contents


Highperformancelasersystemsareneededforcriticallaboratorymissionsandalignedwithseveralcompetencyareas

High-energydensityscience

Directedenergy

Additivemanufacturing

Photo by Kate Hunts/LLNLM. Matthews et al., Optics Express, (2017).

Spacesecurity


AVLISWorld’s highest average power tunable laser

T-REXWorld’s brightest laser gamma-ray source

Heat Capacity LaserWorld’s highest average power solid state laser

Nova PetawattWorld’s highest peak power laser

NIFWorld’s most energetic laser

ARCWorld’s highest energy petawatt system

DPALHigh average power diode pumped alkali laser

MercuryWorld’s highest average power 10Hz laser

HAPLSWorld’s highest average power petawatt-class laser

Compton Source High energy photon Compton source test bed

LLNLhasbeendeliveringleadingedgelaserandopticssolutionsforover40years


Comparedtoflashlamppumping,diodesoffer:

§ Higheraveragepower

§ Greatertotalsystemefficiency

§ Increasedpeakpower

§ Improvedbeamquality

§ Betterreliability

§ Reducedcoolingrequirements

§ Improvedstability

§ Morecompactsystems

§ Reducedoperationalcosts

Diodepumpingistheprimaryenablingtechnologyforhighperformancelasersystems

HAPLS– Worlds’s highestaveragepowerpetawatt-classlaser

HAPLS– World’shighestaveragepowerpetawatt-classlaser

Diodepumpingisagamechanger


DiodelasersareacriticalenablingtechnologyforhighenergylasersystemswhichspantheNIF&PSdirectorate

CoreNIF

DMPA:Diode-pumpingwillincreasesNIFstabilityandenablesgreaterreliableshotenergy

APT

HAPLS:Diode-pumpingenableslowcoststructure($/W)forcommercialapplications

DODT

DPAL:Diode-pumpedalkalilaserenableslowSWaP fordirectedenergyweapons


LaserDiodeTechnologyatLLNL– ManykWtoMW

GOLD– 120Hz,256kW HAPLS– 10Hz,4x800kW


800kW(peak)QCWdiodearrayinaction


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1994 1998 2002 2006 2010 2014 2018

Rela

tive

Norm

aliz

ed S

emic

onuc

tor

Diod

e L

aser

Pro

cure

men

ts

Year

HighpowersemiconductorlasersarebecomingincreasinglyimportantatLLNL

HAPLS– 10Hz,3.2MWGOLD– 120Hz,256kW

1994 1998 2002 2006 2010 2014 2018

HAPLS

GOLD

DPAL

LIFE

Fiber

TACL

Mercury

Year


Whatarethecriticalperformanceparametersforcommercially-availablehighpowerdiodelasers?

Averagepower

Irradiance

E/Oefficiency SpectralwidthCenter

wavelength

Peakpower

Reliability

Cost

Robustness(shock/vibe)

Divergence

www.dilas.comwww.lasertel.comwww.lasertel.com

www.nlight.com


S&Tchallenge– LLNL/DOEdiodepumprequirementsarenotthesameasthosefortypicalindustrialapplications

Commercialrequirements LLNLrequirements

§ Focusonfiber-coupledpumpsfortheindustrialfiberlasermarket

§ Laserheadpower>10Wto<10kW

§ Reliability>10,000hours

§ Temperaturerange:15°Cto35°C

§ Cost istheprimaryconcern

§ Primarywavelengths808and9XXnm

§ CW isimportant

§ LowSWaP isdesirable

§ FocusonbarsandstacksforhighestpeakandCWpowerdensity

§ Laserheadpower>10kWto<10MW

§ Reliability10’sto>1,000’shours

§ Temperaturerange:wider

§ Performance istheprimaryconcern

§ Primarywavelengths7XXand88Xnm

§ CWandQCWarebothimportant

§ LowSWaP iscritical

COTSdiodepumpedsourcesareusuallynotsuitableforLLNLprogramsThismeansourdiode-pumpedlaserprogramsoftenrequiredevelopmentand/orNRE


HowdowepromotediodedevelopmenttomeetLLNLneeds?

Externalcommercialdevelopmentandprocurement

www.lasertel.com

3.2MWdiodebackplaneproducedbyLasertelfortheHAPLSprogram

Examplehighpowerdiodeteststationforassessingeffectsofback-irradiance

Internalresearch,development,andcapabilityinvestments








Contents


Howdoyoumakealasermorepowerful/energetic?

Makeitbigger!

Why?


§ Increasingthecross-sectionalareareducesthermalresistanceandhencethethermalgradient

§ Maximumoutputpowerisstronglydependentonthermalresistance

§ Powerscalingcanbeachieved(tofirstorder)bymakingthelaserlarger

Thermalresistance inhighpowerdiodelasers

https://tinyurl.com/ybvsq77h

0

100

200

300

400

500

0 100 200 300 400

Powe

r (W

)

Current (A)

0.8 K/W

0.4 K/W

0.2 K/W

0.1 K/W

0 K/W

808 nm50% FF cm barCW, 25°C


Wheredidthemissingpowergo?

0

2

4

6

8

10

12

0 2 4 6 8

Powe

r (W

)

Current (A)

Actual

Perfect

808 nmCW, 25°C1.5mm x 0.2mm

0.0

0.5

1.0

1.5

2.0

2.5

0 2 4 6 8

Volta

ge (V

)

Current (A)

Actual

Perfect

808 nmCW, 25°C1.5mm x 0.2mm

0%

20%

40%

60%

80%

0 2 4 6 8

Dist

ribut

ion

of In

put P

ower

Current (A)

Useful Output

Voltage Loss

Threshold Loss

Slope Loss

Actual Voltage Loss21%

Threshold Loss5%

Slope Loss15%

Useful Output59%

I = 8 Amps


Voltageloss– diodelaservoltagedefect

Voltagedefectinadiodelaserisanalogoustoquantumdefectinasolidstatelaser

Epump ElaserVdiodeVphoton

laser

laserpump

EEE -

= defect Quantum

Solidstatelaser Diodelaser

)V()(

241 where

defect Voltage

mλ.

qhc

V

VVV

photon

photon

photondiode

µl»=

-=

heat

P.LeisherandS.Patterson,Proc.ofDEPSSSDLTR,(2013).


Theinternaldifferentialquantumefficiencyηi

representsthefractionofinjectedcarrierswhich(wheninjectedabovethreshold)produceaphotoninsidethelaser

Slopeloss– externaldifferentialquantumefficiency

Theexternal differentialquantumefficiencyηd representsthe

fractionofinjectedcarrierswhich(wheninjectedabovethreshold)produceaphotonthatsuccessfully

leavesthelasercavity

Lowabsorptionlossiskey 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0

2

4

6

8

10

12

0 5 10 15

Volta

ge (V

)

Out

put p

ower

(W)

Current (A)P.LeisherandS.Patterson,Proc.ofDEPSSSDLTR,(2013).

Electrons per second in

Current in, ACoulombs per second

Photons per second out

Power out, WJoules per second

Photons out per electron in

Scale by charge of electron Scale by energy of photon

LaserElectrons

P.Crump,R.Martinsen,P.Leisher,CLEO,(2007).


Sowhathappensasyoutrytodriveadiodelaserharder?

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25

Powe

r (W

)

Current (A)

Actual

Perfect

808 nmCW, 25°C1.5mm x 0.2mm

0%

20%

40%

60%

80%

0 5 10 15 20 25

Dist

ribut

ion

of In

put P

ower

Current (A)

Useful Output

Voltage Loss

Threshold Loss

Slope Loss

Actual

1. Additionalcurrentincreasesheatduetoimperfectefficiency

2. Thefractionofinputpowergoingtoheatincreases(atfirst)duetohighervoltageloss(electricalseriesresistance)

3. Thisself-heatingeventuallycausestheslopeloss(differentialquantumefficiency)togrowexponentiallywithcurrent

4. Eventuallyapointisreachedwheremorecurrentcausesnonetincreaseinpowerduetorapiddecreaseinefficiency0

25

50

75

100

125

150

175

200

0 5 10 15 20 25

Junc

tion

Tem

pera

ture

(ºC)

Current (A)


Whydoesself-heatinglimittheoutputpowerofdiodelasers?

Peak Gain vs Temperature (at N=1.5000e+012cm-2)

Temperature (K)100 200 300

Peak

Gai

n (c

m-1

)

2000

4000

6000

8000

Legend:

PeakGain

0

0.5

1

0.8 0.9 1 1.1 1.2

Ferm

i-Dira

c Di

strib

utio

n

E/Ef

300K77K

0K

Occupied states below this level can contribute to gain

Occupied states above this level do not contribute to gain

1. Differentialgaindecreaseswithincreasingtemperature,somorecarriersareneededtoreachthreshold.This,inturn,increasestheabsorptionlossinthestructure.

P.O.Leisher,etal.,CLEO,(2010).



2. Poorclampingofthegaininsidetheactiveregioncausescarrierdensitieselsewhereinthestructuretoincreaseaswell,furtherincreasingtheabsorptionlosses.

0E+0

1E+17

2E+17

3E+17

4E+17

5E+17

6E+17

7E+17

2.5 3.0 3.5 4.0 4.5 5.0 5.5

Inte

nsity

(ar

bitra

ry u

nits

)

Carr

ier

Dens

ity (c

m-3

)

Position (μm)

375K350K325K300K


From T=300K à 77K, n(T)3 is reduced by ~35X

RAuger ~ C(T)*n(T)3

From T=300K à 77K, C(T) is reduced by ~40X

From T=300K à 77K, RAuger is reduced by ~1400X

Conduction band

Valence band

-Dk Dk

-DE

DE


Electron

Trap

Hole

Ec

EtEi

Ev

Hole

1 2

3or Et – Ei

0.0

0.2

0.4

0.6

0.8

1.0

1.2

50 100 150 200 250 300

Rela

tive

Reco

mbi

natio

n Ra

te

Temperature (K)

Et-Ei = 10 meV

3. Increasingtemperaturecausesnon-radiativerecombinationtoincrease,reducingthedifferentialquantumefficiencyofthedevice.

Shockley-Hall-Reed(trap-assisted)Recombination

P.O.Leisher,etal.,CLEO,(2010).

AugerRecombination








Contents


Howcandiodelaserpowerbescaled?

Option2

Improvethermalmanagement

Option1

Increaseefficiency

0

100

200

300

400

500

600

0 200 400 600

Powe

r (W

)

Current (A)

1.0 K/W

0.6 K/W

0.4 K/W

0.2 K/W

0.1 K/W

880 nmCW, 25C50% FF cm bar

0

100

200

300

400

500

600

0 200 400 600

Powe

r (W

)

Current (A)

45% E/O

53% E/O

60% E/O

68% E/O

76% E/O

880 nmCW, 25C50% FF cm bar


Whydoeslaserdiodeefficiencymatter?

+20%efficiency‒30%inputpower

‒60%coolingor

2.5Xpowerperbar

70% Efficiency

1 kW OpticalOutput

1.4 kW Electrical Input

0.4 kW Heat

50% Efficiency

1 kW OpticalOutput

2.0 kW Electrical Input

1.0 kW Heat

“Efficiencyisn’teverything,butit’sdamnclosetoit…”


Maximumpowercorrelateswellwithconversionefficiency



Voltagedefectreducedbybandgapanddopingoptimization

Primaryoriginsofexcessvoltagedefect:1. Bandgapofwaveguide(turn-onvoltage)2. Bulkconductivityofthep-cladding(resistance)

-7

-6.5

-6

-5.5

-5

-4.5

-4

-3.5

2 2.25 2.5 2.75 3 3.25

Ener

gy B

and

(eV)

Position (um)

Elec FermHole FermCond BandVal Band

0 V

-7

-6.5

-6

-5.5

-5

-4.5

-4

-3.5

2 2.25 2.5 2.75 3 3.25

Ener

gy B

and

(eV)

Position (um)

Elec FermHole FermCond BandVal Band

1.2 V

P.LeisherandS.Patterson,Proc.ofDEPSSSDLTR,(2013).

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 2 3 4 5 6

Pote

ntia

l (V)

Position (um)

Dif ference

0 V

1.2 V

PhotonEnergy

ΔEWG-QW

Rp-clad


Remaininglimitationsofefficiencyinlargeopticalcavitylasers

Lossesinatraditionallargeopticalcavitylaseraredominatedbyfreecarrierabsorptioninthequantumwell


Examplepareto ofthecalculatedabsorptionlossesinalargemodelaserbywherethey

occurinthestructure.

QW73%

p-WG13%

p-Clad7%

n-WG4% n-Clad

3%


1. Freecarrierabsorptionlossesinthequantumwell,aswellasdivergenceangle,canbereducedbymakingthewaveguideverylarge

2. Carefulplacementofthequantumwellensuressingle-modeoperation

3. Doesamuchbetterjobofbalancingthelossesinthestructure(nolongerdominatedbythequantumwell)

Superlargeopticalcavityandd/Γ

Ref

ract

ive

inde

x

Inte

nsity

(arb

uni

ts)

PositionFeng,et.al.,J.ofSemiconductors,vol.30,no.6,(2009).


Thermalresistanceminimizedby:

1. Junction-downbonding(maketheinterfaceasthinaspossible)

2. Newermaterials(increasedthermalconductivity)

3. Improvedcoolerarchitectures(higherheattransfercoefficients)

Thermalresistanceofbroadareadiodelasers

PhotocourtesyofCoherent/DILAS


High-efficiency980nmsingle-emittersforfiber-coupledpumps

0

10

20

30

40

50

60

70

0

2

4

6

8

10

12

14

16

18

0 3 6 9 12 15 18Ef

ficie

ncy

(%)

Out

put p

ower

(W)

Current (A)

976 nmCW, 25°C

95 μm stripe3.8 mm cavity

>16WCWfromsingleemitters(980nm,>68%peakE/O)

0

200

400

600

800

1000

1200

60 61 62 63 64 65 66 67 68 69 70

Freq

uenc

y 980-nm Peak Efficiency Bin

10 devices

L.Bao,J.Wang,M.DeVito,Z.Chen,P.Leisher,etal.,Proc.SPIE,(2011).Disclaimer:Thisexampleselectedfromtheliteratureduetoemphasizemanufacturingdistribution.ThisisnotanendorsementofnLightCorp.oritsproducts.


High-efficiency940nmbarsforpumpingofYb thindisklasers

A.Pietrzak,Proc.SPIE,(2015).

~1kWQCWfromsinglebars(940nm,64%peakE/O)

Disclaimer:Thisexampleselectedfromtheliteratureduetoemphasizemanufacturingdistribution.ThisisnotanendorsementofJenoptik Corp.oritsproducts.








Contents


0

3

6

9

12

15

18

0 4 8 12 16 20Po

wer

(W)

Current (A)

3.8 mm5.0 mm7.6 mm

12345

0 2 4 6 8

Rth

(K/W

)

Length (mm)

Cavitylengthscalingprovidesefficientpathtothermalresistancereductionwithoutcompromisingbeamquality

0

1

2

3

4

5

6

0

2

4

6

8

10

12

14

16

2003 2006 2009 2012 2015 2018

Sing

le-e

mitt

er c

avity

leng

th (m

m)

Rate

d si

ngle

-em

itter

CW

pow

er (W

)

Year

Single-emitteroutputpowerandcavitylengtharecloselycorrelated

WhydidscalingstallatL=5mm?

BasedonreportedresultsbynLight

Improvementsinsingle-emitteroutputpowerenabledbycavitylengthscaling

Root-causeandsolutionnotyetknown

J.Bai,P.Leisher,etal.,Proc.SPIE,(2011).


Othercausesofpowersaturationinhighpowerdiodelasers

SlideprovidedbyP.Crump


§ Athighbias,powers>20W/100μm,extremeconditionsarise— Highcarrierdensity— Hightemperature— Highphotonflux— Highelectricalfieldandhighcurrentdensity

§ Theseleadtointeractingmixofpowersaturationterms,including:— Current-drivenselfheating(degradedthreshold,slope) →(“T0,T1”- wellknown)— Bias-drivenleakage(BDL) →Avrutin— Gainsaturation(orspectralholeburning,SHB) →Peters— Longitudinalspatialholeburning(LSH) →Peters,Leisher— Twophotonabsorption(2PA) →Garrod,Juodawlkis— Waveguidecollapse(WC) →Crump

§ Manycanbeaddressedbydesignimprovements

Briefsummaryofknownfactorsleadingtopowersaturation


Longitudinalspatialholeburning(LSHB)

T. Hao, J. Song, and P. Leisher, Proc. SPIE, (2014).

Spatialnonuniformityinthelongitudinalgainprofileiscausedbyextremeasymmetryoflongcavity(>2mm)

devicesandresultsinreductioninthelaserdiodeoutputpower


ExperimentalsetuptotestforpresenceofLSHB

10

20

30

40

50

60

70

80

90

0.0 0.4 0.8 1.2 1.6 2.0 2.4

Aver

age

Gre

y Va

lue

Current (A)

MeasuredPerfect

!"# = %&'

808 nm, 100 μm x 1500μm

T.Hao,J.Song,andP.Leisher,Proc.SPIE,(2014).


LSHB– modeledvs.measuredresults

5.0E+36

1.0E+37

1.5E+37

2.0E+37

2.5E+37

3.0E+37

73

78

83

88

93

98

0 300 600 900 1200 1500

N2(1

/cm

6 )

Gre

y Va

lue

Cavity Length (μm)

1.3A measured1.3A calculatedw/o LSHB

PR HR

5.0E+36

1.0E+37

1.5E+37

2.0E+37

2.5E+37

3.0E+37

73

78

83

88

93

98

0 300 600 900 1200 1500

N2(1

/cm

6 )

Gre

y Va

lue

Cavity Length (μm)

2.4A measured2.4A calculatedw/o LSHB

PR HR

T.Hao,J.Song,andP.Leisher,Proc.SPIE,(2014).

DirectobservationofLSHBconfirmsitspresenceandaffectondiodelaserperformance


Challenge:samedatareproduciblewithdifferentmodels








Contents


Semiconductorlasersfailgraduallyorsuddenly

0

1

2

3

4

5

0 2 4 6Current (A)

Out

put p

ower

(W) Time zero

+ 1 week 3.5 A+ 1 week 4.5 A+ 1 week 6.0 A

Dislocationnetworkgrowth→Increasednonradiativerecombination

Defect-initiatedthermalrunaway→catastrophicoptical(mirror)damage

808nm laser diode

Laser

Sub-mount

Laser

Sub-mount

COMD

808nm laser diode

Laser

Sub-mount

Laser

Sub-mount

COMD

SuddenFailure

GradualDegradation


Catastrophicopticalmirrordamage

0 50 100 150

Inte

nsity

(arb

. uni

ts)

Position (μm)

Local intensityspike (filament)

0 50 100 150

Inte

nsity

(arb

. uni

ts)

Position (μm)

COD

0 50 100 150

Inte

nsity

(arb

. uni

ts)

Position (μm)

COD threshold

0 50 100 150

Inte

nsity

(arb

. uni

ts)

Position (μm)

Local defect

COD threshold

0 50 100 150

Inte

nsity

(arb

. uni

ts)

Position (μm)

Long timescales

COD threshold

0 50 100 150

Inte

nsity

(arb

. uni

ts)

Position (μm)

Short timescales?

COD


1. QuantumWellIntermixing

MitigationofCOMD– Facetpassivation

http://www.intenseco.com/technology/default_pdf.asp M.Peters,V.Rossin,andE.Zucker,USPatentEP1903646B1

Scribe Markslaserbars

1. Wafer section preparation (pre-scribe) 2. Load into modified MBE & evacuate

3. Bar cleave & stack in vacuum 4. Deposit ZnSe, both facets

N.Chand,etal.Electron.Lett.,vol.32,pp.1595–1596,1996.R.Lambert,et.al.,IEEEJ.LightwaveTech.,vol.24,no.2,(2006).

2. Etched/RegrownFacets

3. Si/Si3N4 Passivation 4. ZnSeepitaxialmirroronfacet(EMOF)


MitigationofCOMD– Facetpassivation

R.M.Lammert,et.al.,Proc.SPIE,(2005).

FacetpassivationgreatlyincreasestheCOMDlimit


BulkCODvs.COMD

COD SEMCOD SEM

Facetpassivationmethodologieshavebecomesoeffectivethatmanydiodesnowfailatdefectswithinthebulkofthedevice

BulkCatastrophicOpticalDamage CatastrophicOpticalMirrorDamage








Contents


Definitionoflaserbrightness

Related to the optical invariant

Brightnessisafixedquantityofalasersource.Itcannotbeincreasedthroughtheuseofpassiveopticsalone.


§ Reducedabsorptionlengthat976nmincreasesthresholdfornonlinearities

§ Broadgainbandwidtharound915nmreducestemperaturecontrolrequirements

Applicationofhigh-brightnesspumps– fiberlaserpumping

Highbrightnessenablesnon-linearitysuppressionviahighmodaloverlapwhich

allowsforreducedfiberlength

Highpowerfiberlasersrequirehighbrightnessdiodelaserpumpsources

HighermodalgainShorterfibers

Pump Δλ FWHM QuantumDefect

915nm >50nm 8%

976nm 9nm 5%


Brightpowerislimitedbyearlyrollofchipbrightness

0

0.1

0.2

0.3

0.4

0.5

0.6

0

2

4

6

8

10

12

14

0 3 6 9 12 15

Slow

-Axi

s Li

near

Brig

htne

ss

(BPP

, W/m

m-m

rad)

Pow

er (W

)

Current (A)

LIVrolloverat18WBIVrolloverat10W

60%

65%

70%

75%

80%

85%

90%

0

10

20

30

40

50

60

70

0 3 6 9 12Current (A)

Coup

ling

Effic

ienc

y (%

)

Pow

er (W

)

Fiber-coupled

Collimated

Fiber-couplingefficiencyrollswithdrivecurrent

J.Bai,P.Leisher,etal.,Proc.SPIE,vol.7953,(2011).


Brightnessrollcausedbyslowaxisblooming

0

0.1

0.2

0.3

0.4

0.5

0.6

0

2

4

6

8

10

12

14

0 3 6 9 12 15

Slow

-Axi

s Li

near

Brig

htne

ss

(BPP

, W/m

m-m

rad)

Pow

er (W

)

Current (A)0

2

4

6

8

10

12

14

16

18

0 3 6 9 12 15 18 21

FWH

M S

low

-Axi

s An

gle

(º)

Current (A)

ABOLN (EMOF20-10)3.8 mm chip25ºC

ModelledBaseline

Measured

Causedbyincreaseinslow-axis-divergence(andreductioninbeam

quality)withincreasingdrivecurrent

LIVrolloverat18WBIVrolloverat10W



Shortdescriptionofslowaxisblooming

Diode Stripe (top down view)

Slow Axis Divergence at I1

Slow Axis Divergence at I2 > I1

• Increase in slow axis divergence driven by gradients in the active region temperature • The slow axis divergence in broad area diode lasers increases as the diode drive current

increases• The diode is often capable of providing reliable power well in excess of what can be efficiently

coupled into the fiber.

As the diode drive current increases the spot size increases. overfilling the real space aperture. decreasing fiber coupling and endangering the fiber reliability.Tighter focusing risks overfilling the fiber numerical aperture

Fiber acceptance angle

Diode Stripe

Spot overfills aperture

Ascurrentincreases,slow-axisbloomingoverfillstheacceptanceNAofthefiber

ImagecourtesyofS.Patterson


Time-resolvedindexmodelasafunctionofdrivecurrent

CW, Junction down, 3.8mm, 1.4 etch depth

3.399

3.400

3.401

3.402

3.403

3.404

3.405

3.406

1.18 1.20 1.22 1.24 1.26 1.28 1.30 1.32

Inde

x of

Ref

ract

ion

Position Along Slow Axis (mm)

3W

6W

9W

0W

CW, Junction down, 3.8mm

0.0E+00

2.0E-04

4.0E-04

6.0E-04

8.0E-04

1.0E-03

1.2E-03

1.4E-03

1.6E-03

0 3 6 9 12 15In

dex

Diff

eren

ce (Δ

n)Current (A)

Δn


Slow-axisbloomingiscausedbythermallensingalongtheslowaxisofthediodelaser


Mitigationofthermallensing:1)Engineertheheatsource

Longercavitylengths→Higherrateablepower



-20 -15 -10 -5 0 5 10 15 20

Slow

-Axi

s Fa

r Fie

ld In

tens

ity

(arb

. uni

ts)

Angle (º)

CW, 25ºC12 Amps

Controldesign

Experimentaldesign

Mitigationofthermallensing:2)Engineertheheatflow

AuPlating

Chip


Promote1Dheatflowtoreducelateralgradientbyformingvoidsinthebondlineoneithersideoftheemitter

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30%

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0 10 20 30 40 50 60 70 80 90 100Gold thermal path thickness h (µm)

Thermal resistance

Temperature gradient

Emitter

Gold pad

Front view after bondingTop view before bonding

X-view after bondingX-view before bonding

Front view after bondingTop view before bonding

X-view after bondingX-view before bonding


§ AdvancedlaserdevelopmentatLLNLrequiresanddriveshighpowerdiodelaserdevelopment

§ Self-heating theprimarycauseofpowersaturation

§ Efficiency isking– itisbettertonotgeneratetheheatthantrytodealwithit

§ Scalingcavitylengthhasenabledrecentimprovements(5mm,<1%outputcoupler)

§ Second-ordereffectsnowlimitfurtherscaling,andthesearenotwellunderstood

§ Reliabilityisnotthemainlimitationforincreasedoperatingpower

§ Brightnessmatters– youneedtobeabletousethelightyougenerate

§ Areyouinterestedinworkingonthistopic?→Severalpost-doctoralopportunitiesintheareasofphotonicsandhighpowerlasers

Concludingremarks

MainentrancetoNIF

NIFtargetbay

Advancements in High Efficiency Semiconductor Lasers for ......2 LLNL-PRES-741702 –P. Leisher...

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Transcript of Advancements in High Efficiency Semiconductor Lasers for ......2 LLNL-PRES-741702 –P. Leisher...