Laser Transmitter for the Tropospheric Wind Lidar Technology Experiment TWiLiTE Floyd Hovis, Fiberte

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Laser Transmitter for the Tropospheric Wind Lidar
Technology Experiment (TWiLiTE)Floyd Hovis,
Fibertek, Inc. Bruce Gentry, NASA Goddard Space
Flight Center
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Laser Transmitter Specifications
Performance Specifications/Design Performance
Summary Table
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Environmental Design Performance
Environmental Design Parameters - Laser Optics
Module
Assumes thermal interface plate maintained at
nominal operating temperature /-2C
Environmental Design Parameters - Laser
Electronics Unit
Assumes liquid cooled interface plate for low
pressure operation
Design performance exceeds all environmental
performance specifications
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BalloonWinds, Raytheon, and Air Force Lasers
Provided Basis For Key Design Features
Electronics module
Laser module
Space-Winds Lidar Laser Transmitter
Final acceptance testing was completed in
November 2006
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Laser Transmitter
Conceptual Optical Layout
Optical isolator
LBO doubler
LBO tripler
Power amplifier
532/1064 nm output
Fiber port
355 nm output
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Laser Housing Baseline Design Full Assembly
Coolant connection

• Dual compartment optical
• cavity
• Oscillator and amplifier
• on opposite sides
• I-beam like structure for
• increased stiffness
• No pressure induced
• distortion of primary
• mounting plate
• Conductively cooling to liquid
• cooled center plane
• Hermetic sealing for low
• pressure operation

Purge port
Signal connectors
Power connectors
Coolant connection
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Laser Housing Baseline DesignOscillator
Compartment
Ring Resonator
Purge port
355 nm nm output window
Coolant connection
1064 532 nm output window
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Laser Housing Baseline Design Amplifier
Compartment
Amplifier
SHG
THG
Purge port
Coolant connection
1064/532 nm output port, external beam dump to be
added
355 nm output port, external beam expander to be
added
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Laser Housing Baseline Design Oscillator
Compartment Size
Top View
31 cm

• An 31 cm x 25 cm x 14 cm canister accommodates
  all required optical and electrical components
• I-beam like mounting structure provides high
  mechanical stability
• All optical components are mounted to a surface
  that to first order does not experience pressure
  induced deformation

25 cm
Side View
14 cm
31 cm
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Ring Oscillator Performance Overview
1 mm Resonator Design Parameters
Diode Bars Eight 6-bar arrays, 100 W rated-QCW,
operated at 75 W peak power per
bar Pulsewidth 56 ms Repetition rate 200
Hz Pump Energy 0.202 J Heat Dissipation 250
watts Slab Size 4.2 x 4.2 x 94 mm3 Doping
Level 1.1 Nd3 Angle of Incidence 57 TIR
Bounces 12 per pass Cavity Length 40 cm
(physical) Cavity Magnification 1.5 Out-Coupling
40 Output Pulse Energy 25 mJ Output
Pulsewidth 13-15 ns Output Beam Size 3 mm
super gaussian (variable)
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Power Amplifier Design
Brewster Angle Slab Design Features
? Even bounce Brewster angle design reduces
beam pointing change due to slab
movement ? Equal number of 10 bar arrays per
string (5) simplifies diode driver
electrical design ? Modeling assuming 100
W/bar arrays are operated at 75 W/ bar
predicts 100 mJ/pulse output for 25
mJ/pulse input for 63 µs pump pulses
? Mechanical mounts will be scaled down
version of NASA Ozone designs
Modeling predicts that extracting a power
amplifier with 25 mJ/pulse achieves 100 mJ/pulse
output at 1.3 duty cycle
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Third Harmonic GenerationResults Of Fibertek IRD

• ? Characterized Type I LBO doubler for higher
  damage threshold and linearly polarized residual
  1064 nm
• - Damage was an issue in early testing with KTP
• - LBO damage threshold is 4X that of KTP
• - Low cost (relatively), high quality LBO
  crystals are now commercially available
• ? Characterized 25 mm Type II LBO tripler
• - High quality, low cost (relatively) has
  recently become available
• - Ion beam sputtered AR coatings have
  demonstrated high damage thresholds and low
• reflectivities for triple AR coatings
  (1064/532/355 nm)
• ? Space-qualifiable laser delivered to Raytheon
  achieved 23 W of 355 nm for 44 W of 1064 nm pump
  at
• 50 Hz (52 conversion efficiency)

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Opto-Mechanical Design and Procurement Status

• Optical design is complete
• Long lead optical components are on order
• 808 nm pump diodes
• Zigzag slabs for oscillator, preamplifier, and
  amplifier
• Mechanical designs of diode pumped laser heads
  are complete
• Parts have been ordered
• Design of laser canister is nearly complete
• Some detailing of amplifier optical train and
  external interfaces remains to be done
• Goal is to order canister in February 2007

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Electronics Overview

• Laser Module electronics
• Q-Switch Driver (high-voltage converter,
  high-voltage switch)
• Photo-detector (detects cavity resonance)
• SHG/THG Heaters and temperature sensors
• Cavity Modulator
• Seed Laser Electronics
• Laser Electronics Unit
• Power input, filtering, conversion and
  distribution
• Diode Drivers (voltage converter, high-current
  pulse switching)
• Cavity modulator driver (HV power amplifier)
• Laser Controller board (pulse timing, system
  interface, controls)
• Temperature Control Boards
• Safety Interlocks
• All electrical designs were previously developed
  for the BalloonWinds and Raytheon Wind Lidar
  laser transmitters

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Software Interface Is Complete
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Electronics Design and Procurement Status

• Software design is complete
• Design upgrades to allow high altitude unsealed
  operation is well underway
• Original plan was for commercial power
  electronics
• Laser control board design complete
• Power supply design complete
• Diode driver design complete
• Logic power supply design complete
• Safety controller design in work
• Updated seeding circuitry in work
• Crystal oven controller in work
• Key long lead components are on order
• High power, high reliability DC/DC converters
• High reliability EMI filter modules (MIL-STD-461C
  D)
• Hermetic capacitors
• Electronics are scheduled to be finished in April
  2007

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Laser Subsystem Summary

• Mass
• Laser Optics Module - 16 kg (based on current
  design)
• Laser Electronics Unit - 22 kg (estimated from
  BalloonWinds, may decrease
• Volume
• Laser Optics Module - 31 cm x 25 cm x 14 cm
  10,850 cm3 (based on current design)
• Laser Electronics Unit - TBD, expected to be
  somewhat larger than laser
• Power
• Estimated total 28 VDC power into system is 470 W
  
• Thermal
• Estimated total power dissipation is 450 W
• Estimated power dissipation Laser Optics Module
  is 250 W
• Estimated power dissipation Laser Electronics
  Unit 200 W
• Laser subsystem delivery in July 2007

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Acknowledgements
Funding for this program was provided by the NASA
Earth Science Technology Office as part of the
Instrument Incubator Program