1. 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

2. JTO Investments
Lasers-what are they good for?

3. 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

4. Army Directed Energy Programs
1984 - 1999
Neutral Particle
Beam Program
1974 - 1993
Ground Based
Free Electron Laser
Mid-Infrared Advanced
Chemical Laser (MIRACL)
Tactical High
Energy Laser
(THEL)
Solid State
Heat Capacity Laser
1995 - 2001
1990 - 2008
1997 - 2004
2001 - 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

5. 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

6. Play Movie
Movie

7. Airborne Laser
7

8. 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.

9. 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.

10. Types of Scalable Solid State Lasers
• Slab
– Crystalline
– Ceramic
– Waveguide
• Disk
• Fiber
– Dual clad
– Large Mode Area
– Specialty fibers
d
D
indium
pump radiation
heat sink
thin disk
laser beam
o.c. mirror
pump radiation
Diode Pumping greatly improves efficiency
but arrays are costly

11. 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

12. 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)

13. 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
13
Status

14. Technology Status
Single 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% eff
Fiber 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
?

15. 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)

16. 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

17. Fused Silica Fiber Parameters
The 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

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

19. 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

20. 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
TRANSITIO
N

21. 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, etcEstimatedDamage
Threshold(J/cm2)
Nd, Yb
Er
Ho, Tm
Zuclich et al, Proc. SPIE 2391, 1995

22. 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
QC
laser
array Collimating
lens
Grating
Output
Coupler

23. III-Nitride Semiconductors

24. Deep UV LED Progress
260 280 300 320 340 360 380
1
10
100
1000
10000
100000
J= 100 A/cm2
PowerOutputDensity(mW/cm2
)
Wavelength (nm)

25. Cree CW laser lifetimes
LifeTime(Hrs)
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 nm
236 hrs at 375 nm
1 min 358 nm
~ 1 sec 348 nm

26. Advanced Sensors (Chem/Bio, mass)
Optics & Photonics
Research
Applied Sensor
Research
Cold Atom Optics
Laser Pulse-Shaping
MEMSPhotoacoustics
SERS
RecognitionElem
ents
Biological Sensor
Research
Cell-basedSensor

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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
32

33. 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.
33