SWIR Lasers for LADAR Applications

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SWIR Lasers for LADAR Applications

• Jack McCarthy, Daniel Creeden, Peter Ketteridge
  Evan Chicklis
• BAE Systems, EIS
• Feb 2007

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Mid-IR Lasers
MIRVLS
DAIRCM
Cryo-Cooled Lamp Diode - Pumped 2micron Lasers
ZGP OPO
Mid-IR Lasers
Stirling Cycle Cooled Technology Packaged Lasers
Room Temperature 2micron Holmium
Laser Technology / Packaged Lasers
Room Temperature 2micron Thulium Laser Technology
ARPA I Multiband Laser
BIV Laser
ARPA II
LAMBS
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Advanced Materials

• Developer of Novel Optical Crystals and
  Semiconductor Materials for Laser and EO Systems
• Solid State Laser Materials
• ZnGeP2
• AgGaSe2, CdGeAs2
• Semiconductor Laser Materials
• Optically Patterned GaAs
• GaSb waveguide Sources
• Novel Optical elements
• Chalcogenide Materials
• Photonic Bandgap Sources
• Photonic Filters

Melt-grown ZGP crystals for wavelength converters
OPGaAs Patterned GaAs OPO devices
Novel Non Linear Optical Components
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SWIR Lasers All Conduction Cooled

• Developing Advanced SWIR Laser Technologies
• High Energy Solid State Lasers
• Diode Pumped High Storage NdYag Designators and
  Illuminators (Sniper Advanced Targeting Pod,
  ATP)
• Diode Pumped Er-Yag High Energy Eyesafe Flash
  Ladar Transmitters
• High PRF Solid State Lasers
• Diode Pumped High PRF Nd (3D LADAR Tx)
• Frequency Conversion to Harmonics Eyesafe
• Fiber Lasers
• Yb Fiber Laser Transmitter
• 1ns Fiber Laser Tx (1 1.5 microns)
• THz Transmitter

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Diode Pumped NdYAG Designator/Rangefinder
Advanced Targeting Pod (ATP) deployed on
F/A-18 -300 mJ, 20 ns, 20 Hz, 1064 nm -100 mJ, 13
ns, 10 Hz, 1570 nm -16 lbs, 168 unit production
lot Next Generation -100 mJ, 20 ns, 20 Hz, 1064
nm -3.3 lbs, Battery Operated Derivative
Products -Eyesafe Harmonics
Hardware - Conduction Cooled and Flight Qualified
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High PRF NdYVO4 Transmitter

• CW Diode pumped NdYVO4 operating at 1064 nm
  provides
• Efficient 5 -8 W source (1064nm), 100 duty
  factor, near diffraction limited
• Conduction cooled, low part count, simple
  configuration, low cost
• Scalable via higher power pump diodes/Added
  amplifier stages
• Remote fiber coupled pump provides minimal heat
  load/weight on gimbal
• Pump laser engine for NIR OPO Driver
• Intracavity OPO in NCMP KTP/KTA
• External Cavity PPLN

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High PRF NdYVO4 Transmitter Performance
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Fiber Laser Replacement - Why?

• Compact, efficient pulse amplification
• gt15 wall-plug efficiency
• High optical efficiency
• Low cost and lightweight
• COTS components
• No free-space coupling
• Large gain-bandwidth
• Can amplify signals from lt1000nm to gt1150nm
• Pulse flexibility
• Variable PRF (lt1kHz to gt1MHz) and pulse widths
  (lt500ps to gt1ms)
• Can generate high peak power pulses with a low
  pulse energy
• Power scaleable

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Semiconductor Seed Oscillator
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Bulk vs. Fiber
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System Architecture Distributed Staging
Pre-Amplification
Power Amplification
Pump Diodes
Pump Diodes
SM Yb-doped fiber
SM Yb-doped fiber
15 µm LMA Yb-doped
20 µm LMA Yb-doped
30 µm LMA Yb-doped
Isolator
ASE Filter
1064nm Seed Diode
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Results

• Developed all-fiber MOFA for high peak-power
  pulse amplification
• Distributed staging design for suppression of
  nonlinear effects

19W pump at 975nm
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Results All Fiber Configuration

• High peak-power and pulse energy
• Peak powers gt250kW with pulse energies gt250µJ (20
  kHz, 1ns)
• Peak powers gt35 kW with pulse energies gt350 µJ
  (20 kHz, 10ns)
• Achieved pulse energies gt650 µJ at 10 kHz, 10ns
  (not shown on plots)
• Variable pulse width and PRF control for
  different applications

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Pulse Characteristics
Spatial Profile

• Clean spectrum
• Stable pulses
• Good spatial output
• M2 measured to be lt1.5

Temporal Profile
M2lt1.5
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Significance

• Efficient, high power source for 1064nm pulses
• No active optical alignment
• Repeatable fiber splicing
• No free-space coupling
• Mitigation of deleterious nonlinear effects
• Completely wave-guided source
• All light and amplification contained in the
  fiber
• Mechanically robust, monolithic source
• Total pulse control
• Independent control of pulse width and repetition
  frequency
• Easily scaleable to higher powers
• Linearly scaleable ? 30µm up to 100µm core fibers
  with SM operation
• Flexible architecture for driving nonlinear
  processes
• THz generation

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Terahertz Spectrum

• Gap between IR and RF frequencies
• High THz absorption in atmosphere
• Must operate in THz transmission windows
• Little to no background at THz wavelengths

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Why Terahertz?

• Imaging applications
• Low loss through paper, cotton, fabrics, etc.
• Non-ionizing radiation
• View metallic objects through clothing
• Real-time security screening
• IR Blind imaging
• Spectroscopic applications
• Materials have distinct absorption spectra in the
  THz region
• Enables chemical and explosive (and possibly IED)
  detection
• Post office mail screening
• Airport use check for explosives in baggage
• Port Security scan shipping containers

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Our Approach Fiber Pumped DFM

• Difference frequency mixing (DFM)
• Amplify two near-IR (NIR) signals in a fiber
  amplifier chain
• Mix signals in a nonlinear crystal (ZGP)
• Difference frequency between the two signals is
  in the THz region
• Resultant THz signal will have high average and
  peak-power
• Phase-matching conditions
• Conservation of energy
• Conservation of momentum (Type I eeo
  interaction)

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Fiber Pump Setup
Preamplifiers
1064 nm
SM fiber
SM fiber
SM fiber
15/130 fiber
SM fiber
SM fiber
SM fiber
1059 nm
20/125 fiber
COL
30/250 fiber
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THz Setup

• Fiber-pumped ZGP
• Pyroelectric detector
• Average-power detection
• Microbolometer array
• THz imaging

Off-axis parabolic mirror
THz filter
Detector
THz filter
Fiber Pump
ZGP Crystal
Collimator
Off-axis parabolic mirror
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Fiber Pumped THz Source

• 2mW average power output at 2.45THz
• 40W peak power at 100kHz PRF with 0.5ns pulses
• Optical conversion efficiency gt0.1
• Mixing 1055nm and 1064.2nm to get 122µm (2.45THz)
• Tunable in THz wavelength from 0.8-2.45THz
• By tuning one pump wavelength, we can tune the
  output THz wavelength
• THz output power drops as THz wavelength
  increases
• Due to phase-matching angle in the crystal
• Tuning limited by seed diodes
• Fiber as a pump allows for a lightweight, compact
  THz source
• ZGP crystal can be integrated into a qualified
  fiber-coupled package

10 mm
Crystal
Fiber
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Results at 2.45THz (100kHz, lt1ns)
Theoretical model accounts for crystal absorption
at pump and THz wavelengths, Fresnel losses,
momentum mismatch, system losses, walk-off
Pump Pulse
Depleted Pump Pulse
Includes crystal absorption at the pump
wavelengths
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Terahertz Imaging Razor Blade
Razor Blade
Razor Blade Image from Inside Tyvek Envelope
Tyvek Envelope
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Terahertz Imaging Pocket Knife
Pocket Knife
Pocket Knife Image from Inside Tyvek Envelope
Tyvek Envelope
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Terahertz Imaging Fiberglass Knife

• Unnoticeable by metal detectors
• Can be seen with THz imaging

Fiberglass Knife
Fiberglass Knife Image from Inside Tyvek Envelope
Tyvek Envelope
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Summary

• SWIR Capabilities
• Designators/rangefinders
• High power, high energy, flight qualified
• LIDAR Systems
• DPSS, conduction cooled, AO Q-switched
• Fiber-based
• Pursuing new technologies
• Fiber-enabled technologies
• Small size, lightweight, less touch labor, COTS
  components
• More optical power efficiently and easily
  scaleable
• Highly efficient optical and electrical
• Off-gimbal operation beam delivery fiber
• Enables the development of new systems at
  different wavelengths