March 27, 2010

Gary L. Wood Army Research Laboratory

UNCLASSIFIED

UNCLASSIFIED

DOD High Energy Solid State Lasers & Selected Laser-Related Efforts at ARL

March 27, 2010

JTO Investments

Lasers-what are they good for?

Lasers-what are they good for?

Commercial industry • Disk readers • Welding, cutting and drilling • Material strengthening (pinging) • Surgical knives • Hair removal • Tattoo removal • Fiber optic communications • Structure fiber sensors • Displays • Printers • Pointers • LASIK • Microlithography • Altimeters

For the military the list includes: • Range finder • Target designator • Wire avoidance • Pointers-mounted to guns • LIDAR • IRCM • Guide star • Fiber guided munitions • Laser artillery igniter Recently • Laser illuminators for warning personnel • Optical communications Future • Directed Energy Weapons • Power Beaming • LADAR • Trackers • Targeting Illuminators • RF Photonics • Smart fuzes • CBRN Sensors

Army Directed Energy Programs

1984 - 1999

Neutral ParticleBeam Program

1974 - 1993

Ground BasedFree Electron Laser Mid-Infrared Advanced

Chemical Laser (MIRACL)

Tactical High Energy Laser

(THEL)

Solid State Heat Capacity Laser

1995 - 2001

1990 - 2008

1997 - 20042001 - 2005

MTHEL

JHPSSL Ph 3

2005 - 2010

Mobile Test Unit

1976

1970 - 1974

Army Tri-Service Laser ZEUS

1998 - 2004

Modular Army Demonstration

System (MADS)

1975

HEL TD

4

Chemical Lasers Solid State Lasers

Present

CO2 Lasers

Scalable Laser types and Issues

• CO2 lasers (10 microns): limited range due to thermal blooming & focused spot fairly large

• Chemical lasers (1.3 & 3.8 microns): limited utility due to toxic and explosive gases, limited run time

• Solid State Lasers (1 micron & 1.5-2.1 microns): Power too low, damage issues

• Alkali-Vapor Lasers (770 - 895 nm): Immature • Free Electron Lasers (tunable): low efficiency,

large size, requires cryogenics

Play Movie Movie

Airborne Laser

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Airborne Laser (ABL)

January 10, 2010 - The Airborne Laser (ABL) research and development platform successfully fired the onboard High Energy Laser (HEL) to engage an instrumented target missile, called a Missile Alternative Range Target Instrument (MARTI). This test demonstrated the full functionality of the ABL system to successfully acquire, track, and engage a boosting target. Test instrumentation aboard the MARTI collected data to evaluate ABL laser system performance. This test engagement was not intended to lethally destroy the missile. The MARTI was launched from San Nicolas Island, located in the Naval Air Warfare Center-Weapons Division Sea Range, off the central California coast. This test provides data to support the ABL platform's attempt of the first lethal shootdown of a boosting ballistic missile using directed energy technology, scheduled for 2010.

Airborne laser testbed successful in lethal intercept experiment

•At 8:44 p.m. PST Feb. 11, 2010 a short-range threat-representative ballistic missile was launched from an at-sea mobile launch platform. Within seconds, the Airborne Laser Testbed used onboard sensors to detect the boosting missile and used a low-energy laser to track the target. The Airborne Laser Testbed then fired a second low-energy laser to measure and compensate for atmospheric disturbance. Finally, the Airborne Laser Testbed fired its megawatt-class High Energy Laser, heating the boosting ballistic missile to critical structural failure. The entire engagement occurred within two minutes of the target missile launch, while its rocket motors were still thrusting. •This was the first directed energy lethal intercept demonstration against a liquid-fuel boosting ballistic missile target from an airborne platform. •It took just a few seconds for the beam to create a stress fracture in the missile, triggering it to split into pieces.

Types of Scalable Solid State Lasers

• Slab – Crystalline – Ceramic – Waveguide

• Disk • Fiber

– Dual clad – Large Mode Area – Specialty fibers

d

D

indiumpump radiation

heat sink

thin disk

laser beam

o.c. mirror

pump radiation

Diode Pumping greatly improves efficiency but arrays are costly

Solid State Lasers for DEW’s

• Largest Challenge: scale up power to 100’s - 1000 kW while maintaining good beam quality (Diffraction Limit ≤ 2) during 100’s seconds run times

• For multiple apertures, need to effectively beam combine

• Need to reduce thermal energy generation (increase efficiency) and effectively remove thermal energy generated (thermal management).

– Thermal energy in gain media distorts the beam phase front, reduces overall gain, affects the polarization, can lead to damage

• Thermal energy is waste energy in a laser engine. Heat is generated in:

– incomplete conversion of electrical energy to diode pump energy – incomplete conversion of diode pump energy to gain media excitation – incomplete conversion of gain media energy to laser energy

Fieldable Tactical Laser DEW

• Will be 100’s kW & able to efficiently deliver energy on target on demand in an affordable mobile package

• Will be compact with a high power to weight ratio

• Will be rugged, durable, low logistics train and able to operate in unclean environments

• Will be able to operate over multiple mission lifetimes

• Will be safe to operate and sustainable • Soldiers will be able to operate (as opposed to

a team of PhD’s)

Objective: Develop a 100 kW-Class SSL Laboratory Device

• Joint Competition Based Initiative to Grow SSL Power From 1kW to 25kW (Phase 1 & 2) and From 25kW to 100kW (Phase 3) With a Design Suitable for Mobile Platforms

• Joint – High Power Solid State Laser (JHPSSL) Program: Phase 3 Executed by the Army with Northrop Grumman and Textron Systems

Northrop Grumman (NG) Achieved 105kW in FY09; Textron Reached 100kW in FY10

1 kW 100 kW

1999 2009

25 kW 30 kW

2005

SSL Power Generation Over Time

NG Textron

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Status

Technology StatusSingle Aperture Technology

Current Status Estimated Limit

Slab Lasers 10s kW at good BQ, higher with poorer BQ

100s kW

Disk Laser 30 kW single aperture (Boeing) 30 kW/disk w/ 30% effFiber Lasers 50 kW multi-mode-IPG

10 kW STM, broadband-IPG 1 kW STM, SF, PM-Nufern

10s kW

Eye-Safer Laser > 1 kW @ 2 µm, ?BQ Tm fiber, Q-Peak

10s kW

Beam Combining Technology

Current Status Estimated Limit

Coherent 1.2 kW NGAS, 21 GHz linewidth 2 fiber lasers (Oct 09), (tiling 105 kW)

?

Spectral 2 kW combining of four narrow-linewidth (4 different λ’s) photonic crystal fiber amplifiers

?

What makes us think we can get there?

• ~100 kW achieved at NG & Textron with moderate beam quality and (at NG) long run times

• Efficiency continues to improve – Pump diode improvements – Laser architectures continue to improve

• Thermal management continues to improve • Fiber lasers continue to improve • Multiple approaches to power scaling appear possible (no

obvious preferred approach at present) • New Material approaches (engineerable ceramics, optical

quality high thermal conductors, single & polycrystalline laser fibers, highly engineerable PCF, novel non-silica based fibers)

Analysis of the scalability of diffraction limited fiber lasers & amplifiers to high average power

Jay W. Dawson, Michael J. Messerly, Raymond J. Beach, Miroslav Y. Shverdin, Eddy A. Stappaerts, Arun K. Sridharan, Paul H. Pax, John E. Heebner, Craig W. Siders and C.P.J. Barty Lawrence Livermore National Laboratory Abstract: We analyze the scalability of diffraction-limited fiber lasers considering thermal, non-linear, damage and pump coupling limits as well as fiber mode field diameter (MFD) restrictions. We derive new general relationships based upon practical considerations. Our analysis shows that if the fiber’s MFD could be increased arbitrarily, 36 kW of power could be obtained with diffraction-limited quality from a fiber laser or amplifier. This power limit is determined by thermal and non-linear limits that combine to prevent further power scaling, irrespective of increases in mode size. However, limits to the scaling of the MFD may restrict fiber lasers to lower output powers.

Received 20 Jun 2008; revised 1 Aug 2008; accepted 3 Aug 2008; published 13 Aug 2008 (C) 2008 OSA 18 August 2008 / Vol. 16, No. 17 / OPTICS EXPRESS 13266

Fused Silica Fiber ParametersThe first 7 entries are physical constants of fused silica and are unlikely to change. The lower 9 entries reflect current state of the art in technology or assumptions made and likely to evolve with time.

• Rupture modulus of silica glass, Rm = 2460 W/m • Thermal conductivity of silica glass, k = 1.38 W/(m-K) • Convective film coefficient for cooling fiber, h = 10,000 W/(m2-K) • Melt temperature of fused silica, Tm = 1983 K • Change in index with temperature for silica, dn/dT = 11.8X10-6 1/K • Peak Raman gain coefficient gR = 10-13 m/W • Peak Brillouin gain coefficient gB(Δν) = 5X10-11 m/W

• Small signal pump absorption of laser required for efficient operation, A = 20 dB • Assumed laser gain, G = 10 • Ratio of the mode field radius to the core radius, Γ = 0.8 • Optical damage limit, Idamage 10 W/µm2

• Assumed coolant temperature for laser, Tc = 300 K • Pump brightness limit, Ipump = 0.021 W/(µm2-steradian) • Peak core absorption at pump wavelength, αcore = 250 dB/m • Fraction of pump light converted to laser power, ηlaser = 0.84 • Fraction of pump light converted to heat in core, ηheat = 0.1

Pump brightness 0.1 W/(µm2-steradian), not SF

Low Maturity Areas

• Multiple apertures require beam combining which has shown limited power scaling to date (except for tiling approach)

• Isolators (free space and fibers) • Coatings (higher damage resistance reliably) • Fiber couplers • Higher brightness diodes

• SBS suppression techniques: robust? • Specialty fibers • Eyesafer pumps and lasers vs 1 micron ones

ARL’s Efforts in Scalable HEL’s-Enabling Technologies

Technical Approach: • Develop most scalable, engineerable (gradient doped, etc.) ceramic laser gain materials • Develop SS phase conjugators for MOPA power scaling with high beam quality • Develop diamond/SiC-face-cooling approach for scalable heat removal from optical components • Optimize techniques for diode-pumped Er lasers emitting in the most eyesafe wavelength region • Cryo-cooled SSL’s, low-QD schemes • New approach to most scalable eye-safe fiber lasers/amplifiers

Strategy: Conduct basic and applied research in

novel solid-state laser concepts, architectures and components to enable High Energy Laser (HEL) Technology for Army-specific Directed Energy Weapon applications

Army Goal: Mobile high laser power with near diffraction limited beam quality

Current

Future

TRANSITION

High Energy Laser Team – major directions

Our focus: Exploration and early development of potential enabling technologies for high energy / high average power solid-state lasers

We don’t try to scale lasers to DEW-level powers (takes a lot of $$ for pump diodes and other large equipment.)

Main emphasis in recent years: “Eyesafer” wavelengths

Some current topics: ➢ Cryogenic lasers – dopants such as Er

➢ Er fiber lasers

➢ Thermal management

• Beam quality improvement and beam combining, via such processes as SBS

• Novel materials – for lasers, beam combining, beam quality, etcEs

timat

ed D

amag

e Th

resh

old

(J/c

m2 )

Nd, Yb

Er

Ho, Tm

Zuclich et al, Proc. SPIE 2391, 1995

10/25/07

Quantum Cascade/Interband Cascade Lasers

• QCL are semiconductor lasers that operate in the mid- to far- infrared and were first developed in 1994 by Bell Laboratories

• Currently there are over a dozen suppliers within the U.S.

• Northwestern University (Center for Quantum Devices) has the best “hero” data to date (M. Razeghi)

– 0.85 watts at 300K at 35% duty cycle – 0.75 watts at 300K at 25% duty cycle – 0.64 watts at 300K CW

• QCL can be operated from a few percent to 100% duty cycle

Distributed Feedback

QClaserarray Collimatinglens

Grating

OutputCoupler

III-Nitride Semiconductors

Deep UV LED Progress

260 280 300 320 340 360 380

1

10

100

1000

10000

100000

J= 100 A/cm2

Pow

er O

utp

ut D

ensi

ty (m

W/c

m2 )

Wavelength (nm)

Cree CW laser lifetimes

Life

Tim

e (H

rs)

0

0,001

0,01

0,1

1

10

100

1000

Emission Wavelength (nm)345 353,75 362,5 371,25 380

1 mW

4 hrs at 360 nm

130 hrs at 367 nm236 hrs at 375 nm

1 min 358 nm

~ 1 sec 348 nm

Advanced Sensors (Chem/Bio, mass)

Optics & Photonics Research

Applied Sensor Research

Cold Atom Optics

Laser Pulse-Shaping

MEMS Photoacousti

cs

SERS

Recognition Elements

Biological Sensor Research

Cell-based Sensor

Robotic Ladar Program

Objective: Research and build ladar sensors for forming three-dimensional world maps of ground robot surroundings for autonomous navigation and obstacle avoidance.

Rapid room clearing Interior structure mapping Detect

Humans Booby-traps Chemicals Biological agents Nuclear agents

Subterranean passage exploration Explorer PackBot

Payload Box

Packbot Ladar System

•Reduce the size of the Mirror/telescope assembly (1” lens) •Reduce the size of the receiver; quad detector design •Redesign and repackage the high voltage amplifier •Incorporate limiting functions in the receiver module •Eliminate large boards for Ethernet •Rebuild signal processor and power board •Install fiber eyesafer laser

Possible board layout in payload bay

Laser

ADC/FPGA Mirror Drive

Power conditioning

8”

3.75”2”

1”

2.5”

1.5”

3”

1.5”

1.5”

Mirror/telescope assembly

Receiver layout

Force Protection

• Countermeasures – HEL (C-RAM, C-Manpads,…) 100 kW & above – MEL (C-UAV, C-IED, ….) 1-10’s kW – LEL (Dazzlers, sensor blinders, IRCM, …) <

1kw • Counter-Countermeasures (Counter DEW)

– Sensors – Eyes – Structures – Electronics

Eye/Sensor Damage

• Psychological vs Physiological effects, in general: – Physiological effects diminish with time – Psychological effects increase with time

• A number of medical techniques exist to mitigate long term eye damage – Anti-inflammatory medication – Steroids – Light treatment

• 0.2 µJ on night adapted eye reaches the MPE level (for visible to NIR Q-switched pulses, the easiest to cause damage) – This is about 0.5 µJ/cm2 impinging on the eye – ED50 (50% probability of retinal leson) is ~10x MPE at these short pulses

• CCD damage is highly dependent of type of CCD used – Damage occurs at threshold fluences at single pixel failure, next at line outs

then finally as white out. • Fairly robust solutions exist for IR protection at all levels • Visible, eye protection for level 3 agile laser threat is most difficult solution

Current solutions

• Much work has occurred for aviators, issues include: – P43 see through – Night time flying due to transmission reduction – Best spectacles are plastic, employ dielectric

stacks or holographic filters and cost in the ~$2K range (Army can not afford this cost)

• Army laser protection eyewear are dyes, limited λ and cost 10 x less than AF and Navy aviators

Potential Applications for High Energy Laser (HEL) Weapon Systems of Current Interest

• Defeat Rockets, Artillery, and Mortars (RAM) and Man-Portable Surface-to-Air Weapons In-flight

• Standoff Mine Neutralization and Explosive Ordnance Disposal (e.g. Improvised Explosive Devices-IEDs)

• Defeat Anti-Tank Guided Missile/Rocket Propelled Grenade (ATGM/RPG)

• Disrupt / Defeat EO/IR Sensors Used to Detect, Track and Engage Systems

• Ultra-Precision Strike – Kill / Disable Targets with No (Minimal) Collateral Damage

HEL Characteristics

HEL Weapon Systems Will Provide the Commander Unique and Complementary Capabilities

Applications

• Operation at the Speed of Light • Low Cost Per Kill • Precision Application of Energy • Graduated Response • Depth of Magazine

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High Energy Laser Technology Demonstrator (HEL TD)

• HEL TD Program Objective: Demonstrate in a Relevant Operational Environment at HELSTF that a Mobile

Solid State Laser (SSL) Weapon System can Provide an Effective Mission Capability to Counter Rocket, Artillery, And Mortar (C-RAM) Projectiles.

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