Post on 14-Jan-2016
FIBERTEK, INC.
Laser Transmitter for the
BalloonWinds Program
Floyd Hovis, Fibertek, Inc.
Jinxue Wang, Raytheon Space and Airborne Systems
Michael Dehring, Michigan Aerospace Corp.
FIBERTEK, INC.
Program Overview
Program Objectives
Develop a robust, single frequency 355 nm laser for airborne and space-based direct detection wind lidar systems
–All solid-state, diode pumped–Robust packaging–Tolerant of moderate vibration levels during operation–Space-qualifiable design
Incorporate first generation laser transmitters into ground-based and airborne field systems to demonstrate and evaluate designs
–Goddard Lidar Observatory for Winds (GLOW)–Balloon based Doppler wind lidar being developed by Michigan Aerospace and the University of New Hampshire
Iterate designs for improved compatibility with a space-based mission–Lighter and smaller–Radiation hardened electronics
FIBERTEK, INC.Airborne vs. Space-Based Laser Doppler Wind Lidar Requirements
Airborne Space-based
Wavelength UV (355 nm) UV (355 nm)
Pulse energy 5 - 200 mJ 150 - 600 mJ
Repetition rate 50 – 2000 Hz 50 –200 Hz
Vibration environment Operate in 0.3 grms Survive 10 grms
Lifetime 2 x 108 shots 5 x 109 shots
Cooling Conductive to liquid or air Pure conductive coolingcooled heat exchanger
Thermal environment Spec energy in ±5°C band Spec energy in ± 5°C band
Survive 0° to 50°C cycling Survive –30° to70°C cycling
FIBERTEK, INC.
Laser Transmitter Overview
Summary of Approach
An all solid-state diode-pumped laser transmitter featuring:
Injection seeded ring laser Improves emission brightness (M2)
Diode-pumped zigzag slab amplifiers Robust and efficient design for use in space
Advanced E-O phase modulator material Allows high frequency cavity modulation for improved stability injection seeding
Alignment insensitive / boresight Stable and reliable operation over stable 1.0 m cavity and optical bench environment
Conduction cooled Eliminates circulating liquids w/in cavity
High efficiency third harmonic generation Reduces on orbit power requirements
Space-qualifiable electrical design Reduces cost and schedule risk for a future space-based mission
FIBERTEK, INC.
Laser Transmitter Overview
Top Level Laser Space-Based Transmitter Performance Goals
1 µm pulse energy 1 J Required for measurements from space
Final wavelength 355 nm Required for direct detection wind lidar
Pulse Rate 50 –100 Hz Improved data collection rate
THG efficiency > 45% Maximizes 355 nm output
Beam quality M2 < 2 Reduces size of collection optics
Frequency drift < 5 MHz/s Allows Doppler shift measurements
Cooling Conductive Space compatible
Lifetime 3 years Space-mission requirement
FIBERTEK, INC.
Laser Transmitter Overview
BalloonWinds Laser Transmitter Design Goals & Specifications
1 µm pulse energy 230 mJ
355 nm pulse energy 70 mJ Pulse Rate 50
THG efficiency > 30%
355 nm beam quality M2 ~ 2
Frequency stability < 150 MHz
Cooling Conductive
Lifetime 1 billion shots
FIBERTEK, INC.
Laser Transmitter Overview
• The basis for the BalloonWinds laser transmitter design is a system that was developed for NASA Langley with ATIP funding
Fiber-coupled 1 m Seed
Laser
Fiber port
Ring resonator
Expansiontelescope
KTP doubler
355 nm output
LBO tripler
0.5xtelescope
Slabs
Mirror
Mirror
Doveprism
Pump diodes
Pump diodes
Amp #2
Amp #1
FIBERTEK, INC.
Laser Transmitter Overview
1 m Ring Resonator Design
Nd:YAG Pump Head
Diode Pumped Increased efficiency / Reduced size - weight Brewster angle slab Eliminates need for end face coating, high fill factor Conduction cooled Elimination of circulating liquids / increased MTBF
1 m Resonator
Telescopic Ring Resonator Allows better control of the TEM00 like mode size 90˚ Image Rotation Homogenizes beam parameters in 2 axes RTP Based Q-Switch Thermally compensated design / high damage threshold
RTP Based Phase Modulator Provides reduced sensitivity to high frequency vibration Zerodur Optical Bench Boresight stable over environment
Performance Features
Design features address issues associated with stable operation in space
FIBERTEK, INC.
Ring Oscillator Design
Optical Schematic
Design Features
Near stable operation allows trading beam quality against output energy by appropriate choice of mode limiting aperture
30 mJ TEM00, M2 =1.2 at 50 Hz30 mJ TEM00, M2 =1.3 at 100 Hz50 mJ square supergaussian, M2 = 1.2 at 50 Hz
Injection seeding using an RTP phase modulator provides reduced sensitivity to high frequency vibration Zerodur optical bench results in high alignment and boresight stability
1. Reverse wave suppressor2. Cube polarizer3. Odd bounce slab4. Steering wedge5. /2 waveplate6. Mode limiting aperture7. RTP phase modulator8. 45° Dove prism9. Non-imaging telescope10. RTP q-switch
1 2 3 4 5 6 2
2 4 9 5 8 5 7 2
5
10
Seed
FIBERTEK PROPRIETARY
Final Zerodur Optical Bench (12cm x 32cm)
FIBERTEK, INC.Ring Oscillator Design TEM00 Results
50 Hz TEM00 Oscillator Beam Quality Measurements
Output energy 30 mJ/pulse
M2 was 1.2 in both axes
FIBERTEK, INC.Ring Oscillator Design TEM00 Results
100 Hz TEM00 Oscillator Beam Quality Measurements
Output energy 30 mJ/pulse
M2 was 1.2 in non-zigzag axis, 1.3 in zigzag axis
FIBERTEK, INC.Ring Oscillator Design Square Supergaussian Results
50 Hz Square Supergaussian Oscillator Beam Quality MeasurementsOutput energy was 50 mJ/pulse
M2 was 1.2
No hot spots in beam from near field to far field
M2 data Near field profile
FIBERTEK, INC.
NASA ATIP Amplifier Design
Single-Sided Pumped and Cooled Amplifier Design
Diode Pumped Increased efficiency / Reduced size - weight Near Normal incidence Simplifies AR coatings Pump on bounce geometry High gain fill factor, high efficiency Conduction cooled Elimination of circulating liquids / increased MTBF Dove Prism Between Stages Reduced astigmatism
Performance Features
Slabs
Mirror
Mirror
Input from oscillator
Final output
Doveprism
Pump diodes
Pump diodes
Basic design has been validated with NASA ATIP funding
FIBERTEK, INC.NASA ATIP Oscillator/Amplifier Integration
• The ring oscillator and dual stage amplifier have been successfully integrated onto a semi-hardened brass board configuration
– All turning mirrors are lockable, no gimbal mounts
– Position insensitive wedge prisms are used for fine steering
FIBERTEK, INC.Oscillator/Amplifier IntegrationSquare Supergaussian Extraction Results
50 Hz Amplifier Beam Quality Measurements• Input was 50 mJ, M2 = 1.2, supergaussian beam• Output was >340 mJ (17 W), Mx
2 = 1.6, My2 = 1.5,
M2 data Near field beam profile of amplifier#2 output
Beam quality vs. output energy and efficiency are a key lidar system level trades
FIBERTEK, INC.
Third Harmonic Generation
GSFC High Brightness Laser Transmitter Approach
Type II Potassium titanyl phosphate (KTP) for second harmonic generation
High efficiency
Space-qualified for CALIPSO
Type II Lithium triborate (LBO) for third harmonic generation
50% conversion efficiency demonstrated in High Brightness Laser built for Goddard
Space Flight Center
- 100 mJ/pulse at 1064 converted to 50 mJ/pulse at 355 nm, 50 Hz operation
KTP doubler
355 nm output
LBO triplers0.5x reductiontelescope
1064 nminput
/2 @ 1064nm /2 @ 1064nm @ 532 nm
FIBERTEK, INC.
Third Harmonic Generation
355 nm Generation with Ring Oscillator/Single Amp
Oscillator configured for square supergaussian output
Initial testing with previous converter configuration gave low results due to excess SHG
New layout resolved excess SHG conversion
Moved KTP before beam reduction
Achieved 61% SHG with unfocussed beamWent to single LBO THG Back conversion appears to also also decreased THG with 0.5x down scope Achieved 43% conversion with single LBO THG
- 64 mJ/pulse (3.2 W) of 355 nm for 165 mJ/pulse (8.25 W) 1064 nm pump at 50 Hz Further optimization is possible by increasing SHG efficiency to 67%Dual crystal THG will be revisited with a reduced magnification down scope Could reduce damage potential by lowering fluence on LBOChange to SHG in Type I BBO or LBO is being investigated for higher damage thresholds needed for scaling to higher pulse energies
KTP doubler
355 nm output
LBO tripler0.5x reductiontelescope
1064 nminput
/2 @ 1064nm /2 @ 1064nm @ 532 nm
FIBERTEK, INC.BalloonWinds Laser Transmitter Design
Baseline Approach
Requires >3.5 W of high beam quality 355 nm output at 50 Hz
Oscillator design same as NASA ATIP developed ring oscillator Mature ready to build technology
Uses a scaled up Brewster angle amplifier with the thermal & mechanical design developed in the NASA ATIP program Mature ready to build technology On axis beam propagation simplifies optical layout
Power goals have been met with 55 W peak diode pumping 8.8 W, M2 = 1.4 demonstrated at 1064 nm Use of 100 W peak power bars operated at 75 W provide significant design margin
Final optical layout developed Laser canister is 13 cm x 43 cm x 66 cm
FIBERTEK, INC.BalloonWinds Laser Transmitter Design
A Single Amplifier Meets the Balloon Wind Lidar Requirements
Oscillator Configuration 90 µs pump pulse 55 W/bar 100 bars
Oscillator Output 40 mJ/pulse M2 = 1.2
Amplifier Configuration 170 µs pump pulse 55 W/bar 112 bars Vary delay to vary
pump power
Amplifier Output 175 mJ/pulse M2 = 1.4
Low Energy Telescopic Resonator
Amplfier 1 Output vs. 808 nm Pump Pulse Width
808 nm pump pulse width (µs)
0 20 40 60 80 100 120 140 160 180
Amplifier 1 outut energy (mJ)
20
40
60
80
100
120
140
160
180
200
FIBERTEK, INC.BalloonWinds Laser Transmitter Design
Baseline Optical Layout
Ring oscillator section Amplifier section
Harmonic converters
Bench design allows allows for second amplifier for power scaling
43 cm
66 cm
FIBERTEK, INC.
BalloonWinds Laser Transmitter Status
Key optics are on order and due for delivery in late February
Final detailing of the optical bench an canister is nearly complete
An ICD for integration of the laser transmitter into the balloon gondola has been developed and reviewed
The program is on track for a July laser transmitter delivery
FIBERTEK, INC.
Future Development Work
Third harmonic conversion tests with 20 W, 50 Hz 1064 nm pump
Design and testing of 2-sided pumped and cooled amplifiers for scaling to 1 J/pulse 1064 nm output at > 50 Hz
Bending of 1-sided pumped and cooled slabs limits power
scaling
Multiple funding sources and deliverables for 2005-2006
Add two 2-sided pumped and cooled amplifiers to the
existing NASA Langley ATIP laser to scale to >1 J/pulse @
50 Hz and 1064 nm
Deliver a fieldable 1 J, 50 Hz 1064 nm source frequency
converted to 355 nm to Raytheon Space and Airborne Systems
for risk reduction testing
Deliver a fieldable 100 Hz, 1 J, 1064 nm transmitter to the
Air Force Research Labs for test and evaluation
FIBERTEK, INC.
Acknowledgments
We wish to acknowledge the NASA Office of Earth Science, NASA Goddard Space Flight Center, NASA Langley Research Center, the Raytheon Space and Airborne Systems, the Air Force SBIR Program, and the National Oceanic and Atmospheric Administration for their support of this work.