High Average Power Lasers for Future Particle …w3fusion.ph.utexas.edu/ifs/aac2012/files/plenaries/Dawson LLNL-PRES...Report was used as a ... Diode Pump System Pump Injection Seed

LLNL-PRES-560013This 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

High Average Power Lasers for Future Particle Accelerators

Presented to 15th Advanced Accelerator Concepts Workshop (AAC 2012)

Jay W. DawsonTuesday June 12, 2012

Lawrence Livermore National Laboratory LLNL-PRES-5600132

Goal: Go beyond hand-waving0-60 MPH in <4 sec 23,000 lb towing capacity

$16K, 38 MPG Seats 8

Why won’t Chevrolet sell me single vehicle that goes from 0-60 in <4 sec, seats 8, tows 23,000 lbs and gets 38 MPG for $16K?


Outline § Introduction: Lasers for accelerator applications§ Short pulse lasers§ High average power lasers

• State of the art in continuous wave & ultrafast§ Fiber lasers§ Efficiency§ Conclusions


ICFA-ICUIL White Paper on High Power Laser Technology for Accelerators § International effort§ Workshops in Darmstadt,

Germany (2010) and Berkeley, CA (2011)

§ Dielectric Laser Accelerator Workshop in Palo Alto, CA (2011)

§ icfa-usa.jlab.org/archive/newsletter.shtml

§ Report was used as a starting point for this talk


The application of laser technology to accelerators was broadly considered

Laser Parameter UnitsWake Field

Accelerators (10 GeV/Stage)

Dielectric Laser

Accelerators

Gamma-Gamma Collider

Ion Acceleration for Medical

Efficiency % 30 30-40 5 (?) 5

Average Power kW 480 10 90 3

Beam Quality M2 <1.5 <1.2 <1.5 <1.2

Pulse Energy J 32 10-7 to 10-5 5 100

Pulse Width fs 133 100 to 1000 1000 100

Pulse Contrast dB 100 (ns) / 70 (>10 ps) N/A N/A 80 to 120

Repetition Rate kHz 15 105 to 106 106 Micro / 0.05 Macro 0.03

Peak Power PW 0.24 10-10 to 10-7 0.002 >1

Intensity W/cm2 3X1018 ~3X1015 4X1017 >1021

Timing 5 fs Interferometric <100 fs N/A

Several other applications were also considered


§ Short pulses (<1 ps)§ High average powers

• >1 kW up to 500 kW (or more)• Diffraction limited ➱ Thermal management

§ Good (ps) to excellent (fs) timing§ Many applications also need

• High pulse energy (>0.01 J up to 100 J)• High pre-pulse contrast (>80 dB in peak power)

What do the requirements for these lasers have in common?

Laser accelerator applications also need extremely good efficiency


Chirped pulse amplification (CPA) is required for short pulse lasers

D. Strickland, G. Mourou, “Compression of amplified chirped optical pulses,” Optics Communications, vol. 56, pp. 219-221 (1985)


Ti:Sapphire lasers have been engineered to attain very high intensity,1022 W/cm2

HERCULES (University of Michigan) 50 TW, 1.5 J, 30 fs, 1011 contrast Ti:Sapphire Laser Pulses

V. Chvykov, et al, Optics Letters, vol. 31, pp. 1456 (2006)

Laser systems scalable to high average power need R&D to develop similar levels of intensity.


The final compressor requires high efficiency, damage resistant gratings

0 25 50 75

0

25

50

75

col

row

0.00 0.20 0.40 0.60 0.80 1.00cascade_4_02_04_03_2_17C15C_XLS

Diffraction map73.5 deg AOIAve 95.0%RMS 1.2 %

Multi-Layer Dielectric (MLD) grating

MLD Gratings have attained >96% efficiency* and >4J/cm2 damage threshold*** M.D. Perry, et al, Optics Letters, vol 20, pp. 940 (1995)** I. Jovanovic, et al, Boulder Damage Symposium (2004)

Efficiency

Optical Parametric Amplification (OPA) can increase bandwidth


§ Efficiencies of ~30% attained*, 90% possible**§ A generalized version of frequency conversion

§ Thermal effects limit theoretical powers to ~ 13kW§ OPA employing angular beam multiplexing

χ(2) crystal

Pump, ωp

Signal, ωs

Residual pump, ωp

Amplified Signal, ωs

Idler, ωi

ωp = ωs + ωi* L.J. Waxler, et al, Optics Letters, vol. 28 pp. 1245 (2003)** J. Moses, et al, JOSA B, vol 28, pp. 812 (2011)

A. Dubietis, et al, JOSA B, vol. 15, pp. 1135 (1998)

Thermal sensitivity of phase matching

Residual crystal absorption

Z.M. Liao, et al, Optics Letters, vol. 31, pp. 1277 (2006)


High average power lasers need to be efficient to be affordable...

1 kW

10 kW

100 kW

1 MW

§ Quantum defect

• ω is frequency• λ is wavelength• Subscripts— s is signal— p is pump


Low quantum defect is one requirement for efficiency

QD =!s

! p

="p

"s


Low quantum defect also reduces problematic heat deposition

CenterHOT

CoolantCOLD

r

T

Tc

§ Heat deposition causes issues such as— Thermal rupture— Melting— Thermal lensing— Stress-induced birefringence

§ Leads to— Catastrophic failure or— Beam quality degradation


§ Slab: 14 kW, 1.45 XDL*, 28% o-o eff.

Different geometries have been investigated to manage heat§ Rod: 1.03 kW, 2.2 XDL, 17% o-o eff.

§ Fiber: 10kW, 1.2 XDL, ??% o-o eff**, § Thin Disk: 0.496 kW, 1.6 XDL, 35% o-o eff.

E. Honea, et al, Optics Letters, vol 25, pp. 805 (2000)G.D. Goodno, et al, Optics Letters, vol. 31, pp. 1247 (2006)* non-standard definition of beam quality

J. Mende, et al, Proc of the SPIE, vol 7193 (2009)V. Gapontsev, et al, SSDLTR (2009)* typical is 80%, but 10kW attained with fiber laser pump

Cryo-cooling helps the thermal issues


§ Thermal properties improve at cryo temperatures § 2.5J/10Hz/25 fs Cryo-cooled Ti:Sapphire

§ 2.3 kW, 1.9 XDL, 63% o-o eff. § Cryo-cooling enables better beam quality

M. Pittman, et al., Design and characterization of a near-diffraction-limited femtosecond 100-TW 10-Hz high-intensity laser system,” Applied Physics B, vol 74, pp. 529-535 (2002)

T.Y. Fan, et al., “Cryogenic Yb3+-doped solid state lasers,” IEEE JSTQE, vol. 13, pp. 448-459 (2007)

J.K. Brasseur, et al, “2.3-kW continuous operation cryogenic Yb:YAG laser,” Proc of the SPIE, vol 6952 (2008)


Issue: Efficiency means amplifiers need to be saturated, making pulsing an issue

CW

Pulsed

Laser power vs. time Peak pulse power for a 1kW laser

High peak powers lead to optical damage, self phase modulation and other non-linear effects that degrade performance and lead to efficiency compromises

Pulsed lasers with CW efficiency AND good pulse quality are an R&D challenge


§ Fiber (5kHz): 0.01W, 500 fs, 1.8 XDL, 23% o-o eff.

As a result pulsed systems have less impressive average power thus far

§ Cryo (10kHz): 0.105kW, 865 fs, 1.3 XDL, 32% o-o eff

§ Slab (20MHz): 1.1kW, 615 fs, 2.7 XDL, 44% o-o eff. § Fiber (78MHz): 0.83kW, 880 fs, 1.3 XDL, 57% o-o eff*

D.E. Miller, Optics Letters, to be published T. Eidam, et al, Optics Express, vol. 19, pp. 255 (2011)

T. Eidam, et al, Optics Letters, vol. 35, pp. 94, (2010)* 65% pre-compressionP. Russbueldt, et al, Optics Letters, vol. 35, pp. 4169 (2010)


Beam combination creates high power systems from manageable unit cells

S.J. McNaught, et al, Frontiers in Optics (2009)* Group employed non-standard definition of beam quality (B.Q.)

Coherent Laser Combination100 kW, B.Q.~2.9*, Slab Laser (7)

Spectral Laser Combination8.2 kW, M2~4.3, Fiber Laser (4)

C. Wirth, et al., Optics Letters, vol. 36, pp. 3118 (2011)


Beam combination of ultrafast lasers is embryonic in comparison to CW

A. Klenke, et al, ASSP 2012 (2012)

Coherent Laser Combination88W, 3mJ, Rod Type Fibers

Spectral Synthesis of 3 Lasers<500fs from 1ps pulses

W.Z. Chang, et al, CLEO 2012 (2012)


Fiber lasers are promising in efficiency, average power and beam quality

• Rare earth doped core absorbs pump light from cladding• Light propagating in core stimulates emissions leading to brightness enhancement• Optical fiber core defines output beam quality• High surface area to volume ratio of core minimizes thermal effects• High intensity over long lengths lead to highly efficiency process I>>Isat

• Yb3+ fibers can achieve 85% optical to optical conversion efficiencies

People like fiber lasers because they are a simple-to-use, low-maintenance, compact source of high-brightness, high-power laser light with wall plug efficiencies in excess of 30%


Short pulse fiber lasers are challenged in terms of energy and pulse quality

Pulse quality issues from imperfect dispersion balance and SPM are often not

apparent on a linear scale50µm mode

200µm mode

Self-focusing limit

M.Y. Cheng, et al, Optics Letters, vol. 30, pp. 358 (2005)

Record 1ns diffraction limited fiber pulse energy resultC.D. Brooks, et al, Applied Physics Letters, vol. 89, pp. 111119 (2006)

J.W. Dawson, et al, IEEE Journal of Selected Topics in Quantum Electronics, vol. 15, pp. 207, (2009)


Active compensation can help some, but much more R&D is needed

Corrected: 88.7% Strehl 881fs FWHM

Uncorrected: 49.5% Strehl

1126fs FWHM

Transform Limit: 100% Strehl 809fs FWHM

Linear Scale Log Scale

Yet to be published LLNL internal results using SLM to correct residual phase errors on a short pulse fiber laser (Heebner, Phan and Spinka)


LLNL has invested in laser technology over the last 50 years

We are employing the draw tower to investigate new fiber designs that will scale in power and pulse energy


§ Beam Combination of Multiple Lasers

Diode pumped solid state lasers are the only current pathway to efficiency

§ Single Aperture, Diode Pumped Laser § OPA or OPCPA

Injection Seed Laser

Power Amplifier

Heat Removal

Compressor

Diode Pump System

Power Amplifier

Heat Removal Compressor

Diode Pump System

Pump Injection Seed Laser

Signal Injection Seed Laser

OPCPA Amplifier

§ Diode laser arrays exist with 10s of kW


*Your mileage (efficiency) may vary

26

38 MPG Highway*26 MPG City*


State-of-the-art diode lasers have an electrical to optical efficiency of 65%

§ AC to DC power supplies peak around 87% efficiency

§ Cooling will be required• Heat removed/electrical power • Lab Chiller: 47.2% at 0ºC,

80.6% at 20ºC, 107.6% at 40ºC • Heat exchanger: 4860%

assuming cooling water is freeR. Pandey, T. Koenning, K. Alegria, D. Merchen, S. Patterson, P. Wolf, B. Kohler, J. Biesenbach, “An overview of diode lasers for defense applications,” Solid State Diode and Laser Technology Review, Santa Fe, NM (2011)

When AC-DC conversion and cooling are included the efficiency is <65%


So what is the actual wall-plug efficiency of a diode laser?

28

Best diodes today

65% diode electrical to optical efficiency is really 41% wall plug efficiency at 20C

laser power

cooling power

total power

efficiency

Wall-plug efficiency vs. Spec. Sheet

§ LN2 = $0.09/liter (pretty cheap)• N2 heat of vaporization is 5.56 kJ/mol• N2 liquid density is 0.808 g/cm3 at b.p.• N2 molecular weight is 28 g/mol• N2 1.78 MJ/$ of cooling

§ Electricity in US is $0.112/kWh• 15.2 MJ/$ of cooling at 0C• 25.9 MJ/$ of cooling at 20C• 35.6 MJ/$ of cooling at 40C


Cryogenic lasers work better, but are 15X more expensive to operate

!labchiller20C = 0.806

!LN2= 0.0556

Equivalent Efficiency Factor


What is the real wall-plug efficiency of a laser power amplifier?

30

• Continuous wave fiber lasers attain 85% optical to optical efficiency• Pulsed lasers are not going to attain 85% optical to optical efficiency

without a lot of R&D

laser power

cooling power

total power

efficiency

Wall-plug efficiency vs. O-O Efficiency


Converting efficiency to cost illuminates the issue more clearly

31

Utility Cost for 1kW Laser Utility Cost for 1MW Laser


Are there plausible pathways to relevant diode pumped laser efficiencies?

32

Proposed Scheme ηdiode ηpower amp ηcompressor ηbeam combination ηwall-plug

2kW CW Fiber Laser Today 0.41 0.85 1.0 1.0 35%Single Aperture Pulsed Fiber

Laser Current Technology 0.56 0.5 0.85 1.0 24%

Beam Combined Pulsed Fiber Laser Current Technology 0.56 0.5 0.85 0.9 21.4%

Beam Combined Pulsed Fiber Laser (Lab Chiller) Current 0.41 0.5 0.85 0.9 15.7%

Future laser: Improved power amp, gratings + beam comb 0.41 0.81 0.95 0.95 30%

Future Laser (above) with heat exchanger 0.56 0.59 0.95 0.95 30%

Future laser: Improved diodes, amp, gratings + beam comb 0.55 0.8 0.95 0.95 40%

Future laser: Improved power amp, gratings + beam comb II 0.7 0.8 0.95 0.95 50%


§ Modeling & Simulation• Understand scale of the problem• Determine if new ideas are really plausible• Verification and validation

§ 80% efficient 100 fs lasers with high contrast and 15 kHz - 1 MHz repetition rates• How high can an efficient unit cell scale in energy?• New gain materials? Ceramics? New fibers?

§ 95% efficient beam combination of 100 or more ultrafast unit cells

§ Timing of high power lasers to parts of a cycle

Where would R&D investment most benefit this community in the near-term?


§ Short pulse lasers in the few kilowatt power range could be only a few years away

§ Higher power lasers will require more development and will need to be efficient in order to be cost effective

§ Diode pumped solid state lasers are the most promising pathway forward• Fiber lasers are particularly attractive from the

standpoint of efficiency and bandwidth, but need work on pulse quality and energy scaling

Conclusions


LLNL contributors to this talk§ Mike Messerly

§ Matt Prantil

§ Paul Pax

§ Arun Sridharan

§ Graham Allen

§ Derrek Drachenberg

§ Henry Phan

§ John Heebner

§ Chris Ebbers

§ Ray Beach

§ Ed Hartouni

§ Craig Siders

§ Tom Spinka

§ Chris Barty

§ Andy Bayramian

§ Constantin Haefner

§ John Crane

§ Gina Bonanno

§ Felice Albert

§ Howard Lowdermilk

§ Sasha Rubenchik

Documents

High Average Power Lasers for Future Particle …w3fusion.ph.utexas.edu/ifs/aac2012/files/plenaries/Dawson LLNL-PRES...Report was used as a ... Diode Pump System Pump Injection Seed