Presented by: Andy BayramianLawrence Livermore National Laboratory

High Energy Class Diode Pumped Solid State Lasers Workshop

September 12, 2012

Granlibakken Conference Center, Lake Tahoe, CA

Progress towards a Compact Laser Driver for Laser Inertial Fusion Energy

Progress towards a Compact Laser Driver for Laser Inertial Fusion Energy

LLNL-PRES-581132

2

The National Ignition Facility

LIFE is a modular laser system which allows realistic reliability specifications, affecting plant availability by <1%

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1 “Beamline in a box” fits in a semi trailerA >100m NIF beamline is compressed into a <11m box

10.5 x 2.2 x 1.4 m3

Modular, truck-shippable, swappable beamlines enablepractical power plant supply chainhigh availability laser

NIF capability in a very small box:LIFE high average power laser architecture attributes

Provides efficiency (~18%) at high repetition rate (16 Hz)• High brightness efficiency diode pump arrays• Helium gas-cooled amplifiers• High efficiency harmonic conversion using pulse splitting

Will be built with existing materials• Glass slabs: thermal birefringence compensated by architecture• DKDP Pockels cell: polarization switching minimizes heat load

Designed for high availability operation• Robustness: Low 3 fluence operation• Headroom in beamline power to meet operational availability• Optics preparation to mitigate damage

Suitable for remote (off-site) manufacturing• Modular beamlines permit hot-swapping• Separation of laser manufacturing & power generation operations

4 4

55

Laser Bay

Master oscillator / Preamplifier / Multi-pass architecturePassive optical system performanceLine Replaceable Unit (LRU) methodologyWhole-system design, construction, commissioning and operationOptics production and performance experience baseCoupling demonstration to full-scale IFE target

The NIF laser provides the single-shot baseline

NIF Beamline

17 J/cm2 18 J/cm2 3

6

pFlashlamps

pFlashlamps

Laser diodes and helium gas cooling enable a NIF-like architecture to meet LIFE driver requirements

These technologies have been developed as part of the Mercury HAPL Project

High Speed Gas CoolingHigh Power Diode Arrays

3 W/cm2 cooling (average)100 kW peak power

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Diode pumps high efficiency (18%)Helium cooled amps high repetition rate (16 Hz) with low stressNormal amp slabs compensated thermal birefringence, compact ampPassive switching performs at repetition rateLower output fluence less susceptible to optical damage

LIFE combines the NIF architecture with high efficiency, high average power technology

8NIF-0111-20671s2.ppt

16 J/cm2 14.7 J/cm2 3

Rotator /4Diodes Diodes

The entire 1 beamline can be packaged into a box which is 31 m3 while providing 130 kW average power

9

10.5 m

1.35

m

2.2 m

Diode array

Pockels cell

Amplifier head

Preamplifier module (PAM)

Deformable Mirror

LIFE Box in NIF Laser Bay

LLNL average power lasers have been proving grounds for several key LIFE technologies

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J. Honig, et. al, Appl. Opt. 46, 3269 (2007)A.J. Bayramian et. al, Fusion Sci. Tech. 52, 383 (2007)

25 kW high average power laser AVLIS 24/7 operational laser

600W, 10 Hz Mercury Laser 300 Hz, 38 W Pulse Amplifier

Efficiency-cost tradeoffs: Nd vs. Yb gain media

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Efficiency vs. Pump Power vs. Cooling Architecture

Erlandson, et al., Invited Paper, Opt. Mat. Express, 2011; Patent filed: IL-12308

Our results quantify the benefits of advanced materialsshow that cooling architecture is critical to capitalize on Yb:YAG

for 2.2 MJ 3LaserYb:S-FAP

Nd:APG-1

Yb:YAG @ 200 K

Yb:YAG @ 150 K

Yb:S-FAP @ 295 K

Yb:YAG @ 200 K

Yb:YAG @ 232 K

Yb:YAG @ 175 K

Yb:YAG @ 150 K

Nd:APG-1 @ 326 K

125 s164 s

Pulselength = 400 s

300s

164 s300 s

600

1000 s

The LIFE laser will achieve high efficiency, optimized at ~18% to balance economic and performance terms

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12

14

16

18

20

22

24

30 40 50 60 70 80 90

Effic

ienc

y (%

)

Diode Power (GW)

223 s

164 s 125 s 106 s

Pump pulselength

Electrical to 3 Optical Efficiency

variability

83 s

Capital Cost →

Diode power conditioning has been made practical for the footprint and efficiency needed for Beam-in-a-Box

• Smart Pulser— “A more compact and efficient diode pulser”— High average power (12.5 kW)— High current (1000A)— High efficiency (90%) (95% efficiency possible with double size pulser— Low volume diode pulser (713 cm3)— Benefit: 10X average power, 10X decreased volume

• Licensing— This technology is currently being developed by a commercial company

Size: 3.66 x 4.76 x 40.96 cm3

Single pulser unit of Diode Power Conditioning for LIFE

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These pulsers are now being used in the lab for diode laser testing

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0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800

WA

TTS

AMPS

10C0C-17C

0 50 100 150 200 250 300 3500

200

400

600

800

1000

Time (us)

Cur

rent

(am

ps)

97% of energy between 0 and 208 us

0 50 100 150 200 250 300 350 4000

100

200

300

Time (us))

Cur

rent

(am

ps)

1000A dummy load

10-bar diode stack

• Once characterized, these early bar analogs similar to those needed for LIFE will undergo Mshot to Gshot lifetests

• Mshot testing underway now

Example of a bar test with temperature study

0

100

200

300

400

500

600

700

800

900

0.00E+00 5.00E+04 1.00E+05 1.50E+05 2.00E+05

WAT

TS

SHOTS

Optical Power (W)

Early Lifetime testing

Diode technology will meet Beam-in-a-Box cost targets

• White paper co-authored by 14 key laser diode vendors• 2009 Industry Consensus: 3¢/W @ 500 W/bar, with no new R&D

• Power scaling to 850 W/bar provides $0.0176/W (1st plant) • Sustained production of LIFE plants reduces price to ~$0.007/W• Diode costs for first plant: $880M• Diode costs for sustained production: $350M

0.1

1.0

10.0

100.0

0.000 0.001 0.010 0.100 1.000 10.000 100.000

Price (¢/W

 at 5

00W/bar)

Diode Volume (GW)

1

ONE TIME PRODUCTION

SUSTAINEDPRODUCTION

One LIFE Plant

LIFElet1¢ /W

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Each beam box includes ~130 MW of polarization combined diode pumps

Schematic of pump delivery methodDiode relay telescope

Polarizer

Amplifier

Solid model of the LIFE amplifier system

Diode array

Gas-cooled amplifier

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Dio

de

arra

y

Diode array

7.0

5.5

4.0

2.5

1.0

Amplifier Diode Pump Profile (Gain)

-12-10 -8 -6 -4 -2 0 2 4 6 8 10 12

-12-10-8-6-4-202468

1012

X(cm)

Y(cm

)

Ray-trace data

Amplifier heads employ gas-cooled glass slabs to remove heat longitudinally mitigating thermal lensing

This amplifier design was prototyped and thermal / gas cooling codes benchmarked on the Mercury laser system

amplifierslabs

Helium

Pump

Pump

Gas Cooled Amplifier Head

Details

• 20 glass slabs • Aerodynamic vanes• 5 atm Helium • Flow rate Mach 0.1

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Thermally induced depolarization in isotropic media (Nd:glass) can be minimized with polarization rotation

, 4-wave platepolarizers

Pockels cell

Quartz rotator

Spatial filterRelay

RelayAmp 1

Amp 2

Architecture

Polarized transmission of amplifier components

1 slab 1 amplifier(20 slabs)

2 amplifiers(compensated)

1.00.90.80.70.60.50.40.30.20.10.0

1.00.90.80.70.60.50.40.30.20.10.0

1.00.90.80.70.60.50.40.30.20.10.0

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The materials chosen for the LIFE laser are based on today’s availability to meet schedule

KDP and DKDP frequency conversion crystals

Nd3+: phosphate laser glassHEM Sapphire & EFG Sapphire

waveplates

Quartz crystal rotators

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LIFE requires a 25 x 25 cm2 aperture quartz rotator, however, quartz is not yet available in this size

• Quartz crystals can produce a 15 x 15 cm aperture today (Sawyer Corporation)

• Bonding of 4 parts together will yield a full size optic.• We are doing our first test bonds in collaboration with

Precision Photonics Corporation• Polished parts bonded with CADB (Chemically Activated Direct

Bonding)

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Validation experiments on quartz rotator material indicate potential to meet LIFE beamline requirementsFirst characterization of a bonded quartz rotator shows promise

• Transmitted wavefront (<lambda/14 without MRF correction) & rotation (>99.9%) are reasonable for this first demo

• Raster scan damage testing was carried out at SPICA Inc. on three different samples using a 1064 nm 3 ns Nd:YAG laser system.

• First initiation sights were observed at 16 J/cm2, 16 J/cm2 and 49 J/cm2

respectively. • An additional test for 105 shots was successfully carried out at 10 J/cm2

(nominal LIFE operational point for the rotator).

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Bonded Quartz Rotator Transmitted wavefront error(8.0 x 9.0 x 1.4 cm3)

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A cylindrical spatial filter can mitigate manyissues associate with high average power / intensity

• Spatial filters are essential for high energy laser systems– Reset high frequency B-integral effects– Provide gain isolation– Improve laser beam quality

• High intensity in spatial filters is an issue– Exceeds pinhole melt / vaporization

threshold– Pinholes degrade over time– Vaporized material can coat telescope

optics

High Intensity Issues

Cylindrical Filter Approach

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The calculated intensity profile on the cylindrical filter appears acceptable with real aberration files

0 100 200 300 4001x10-2

1x10-1

1x100

1x101

1x102

1x103

1x104

1x105

left right

Flue

nce

(J/c

m2 )

Half Angle (rad)

Fluence map on slit

Design point

Complex field for final pass sent through Cylindrical Telescope in Miro

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Cylindrical filter experiments are proceeding well

Testing apparatus at SPICA showing active test

• Slit filter substrates manufactured using NIF high damage threshold substrate, finishing, and cleaning procedures.

Raster scan test results:

• Successful ramp from 0 - 300 J/cm2 in dry air (RH 5%)

• Successful ramp from 0 - 300 J/cm2 in vacuum (mtorr)

• Single damage spot at 150 J/cm2 in vacuum – no other damage

• Lifetime testing underway to demonstrate 105 shots – so far 3.6x104 shots no damage

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PROP Model with New Optics Aberration Files: Results at Converter Input

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Mean 1 fluence: 6.25 J/cm2

Peak 1 fluence: 6.99 J/cm2

Contrast: 2.23%

• More realistic aberrations using NIF optics database with no scaling• Filtering of files to remove interferometer defects• Wavefront improved slightly compared to original model

High resolution 1024x1024 (500 micron pixels)

Detailed propagation simulation (based on measured NIF optics aberrations) shows excellent performance

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Energy = 5.5 kJMean fluence = 1.55 J/cm2

Contrast = 6.5%

Beam contrast at the final Fresnel optic is reasonable

Focal spot at hohlraum clears the laser entrance hole

Fluence (J/cm2)

2.5

2.0

1.5

1.0

0.5

0.0-30 -20 -10 0 10 20 30X (cm)

30

20

10

0

-10

-20

-30

Y (c

m)

Outer illumination cone shown with allowances for pointing/plasma closure

3 optical damage can be mitigated using existing NIF technologies and fluence scaling

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Fused Silica Lenses

Tremendous progress has been made improving the damage resistance of

optics for NIF

0 5 10 15 20 25100

101

102

103

104

105

106

107

AfterMitigation

2009finish

1997finish

3w Fluence Distribution 1.8MJ NIF, 1000 Shots

2010 AMPTreatment

Initi

atio

ns p

er N

IF-s

ize

Opt

ic

3 3ns fluence (J/cm2)

Beam Contrast 10%

LIFE: average fluence reduced by >2X to add margin against modulation for

high average power

Fused Silica Lenses

0 5 10 15 20 25100

101

102

103

104

105

106

107

3w Fluence Distribution LIFE, 1e9 Shots

After Mitigation

2010 AMPTreatment

Initi

atio

ns p

er N

IF-s

ize

Opt

ic

3 3ns fluence (J/cm2)

Beam Contrast 10%KDP

Final optic

NIF capability in a very small box:LIFE high average power laser architecture attributes

Provides efficiency (~18%) at high repetition rate (16 Hz)• High Brightness efficiency diode pump arrays• Helium gas-cooled amplifiers• High efficiency harmonic conversion using pulse splitting

Will be built with existing materials• Glass slabs: thermal birefringence compensated by architecture• DKDP Pockels cell: polarization switching minimizes heat load

Designed for high availability operation• Robustness: Low 3 fluence operation• Headroom in beamline power to meet operational availability• Optics preparation to mitigate damage

Suitable for remote (off-site) manufacturing• Modular beamlines permit hot-swapping• Separation of laser manufacturing & power generation operations

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Bob DeriAndy BayramianGlenn BeerChuck BoleyJeff BudeAmber BullingtonDiana ChenAl ErlandsonSteve FulkersonGlenn HueteTravis LangeRod Lanning

Mark HenesianKen Manes

Naresh MehtaShahida Rana

Margareta RehakSam Rodriguez

Kathleen SchaffersMary Spaeth

Chris StolzTayyab SuratwalaJohn Trendholme

Steve Telford

LIFE laser/laser materials team