Title: Laser Transmitter Development for Airborne Direct Detection Wind Lidar and High Spectral Resolution Lidar Missions F. E. Hovis, J. Edelman, T. Schum, J. Rudd, and K. Andes Fibertek, Inc., 510 Herndon Parkway, Herndon,
1Laser Transmitter Development for Airborne Direct
Detection Wind Lidar and High Spectral Resolution
Lidar Missions
F. E. Hovis, J. Edelman, T. Schum, J. Rudd, and
K. Andes Fibertek, Inc., 510 Herndon Parkway,
Herndon, VA 20170-5225 Bruce Gentry, NASA
Goddard Space Flight Center
Anthony Cook, Chris Hostetler,
and John HairNASA Langley Research Center
2Program Overview
- Single frequency laser transmitters for NASA
Instrument Incubator Programs - TWiLiTE (Tropospheric Wind Lidar Technology
Experiment) laser transmitter - 355 nm single frequency
- Operate in an unpressurized high altitude
aircraft - Direct detection Doppler wind lidar
- Source/Pump laser transmitter for High Spectral
Resolution Lidar(HSRL)/Ozone DIAL system - Single frequency 1064/532/355 nm laser
transmitter - Multi-wavelength HSRL transmitter
- 1064 nm and 355 nm pumps for Ozone DIAL
- Used to generate used to generate 300/320 nm
- Goal is a design that can meet the requirements
of both programs
3Laser Transmitter Specifications
Performance Specifications/Design Performance
Summary Table
Parameter TWiLiTE HSRL/Ozone DIAL
Repetition rate (Hz) 200 200
Pulse energy 30 mJ _at_ 355 nm Channel 1 - 100 mJ _at_ 1064 nm Channel 2 - 45 mJ _at_ 355 nm 35 mJ _at_ 532 nm 20 mJ _at_ 1064 nm
Beam quality (M2) lt3 lt2 at all wavelengths
Pulse width gt15 ns lt10 ns
Power consumption lt550 W lt1500 W
Seeding efficiency 99.9 99
Frequency stability lt 5 MHz RMS for 30 s lt 5 MHz RMS for 30 s
A single frequency 1064 nm transmitter capable
of dual 20 W outputs meets the needs of both
lidar systems
4Laser Optics Module Environmental TWiLiTE
Specifications
Environmental Specifications - Laser Optics Module
Parameter Operating range Survival range
Ambient temperature (C) 25?5 -40 to50
Ambient pressure (mbar) 1010?25 35 to 1010
Environmental Design Parameters - Laser Optics
Module
Parameter Operating range Survival range
Ambient temperature (C) 10 to 40 -40 to 50
Ambient pressure (mbar) 0 to 1050 0 to 1050
Assumes thermal interface plate maintained at
nominal operating temperature /-2C
TWiLiTE environmental specifications drive the
mechanical design
5BalloonWinds, Space Winds, and Air Force Lasers
Provided Basis For Key Design Features
Design Features
Electronics module
Laser module
Laser Transmitter Modules
6Space Winds Transmitter Performance Summary
Parameter Performance Repetition rate 50
Hz Pulse energy at 1064 nm 888 mJ 3rd
harmonic conversion eff. 53.8 Pulse energy at
355 nm 478 mJ 28 VDC power consumption 684
W 1064 nm wall plug efficiency 6.5 (1064 nm
laser output to 28 VDC input) 355 nm wall plug
efficiency 3.5 (355 nm laser output to 28 VDC
input) Beam quality at 1064 nm, M2 2.2 (hor.
axis), 2.3 (vert. axis) Beam quality at 355 nm,
M2 4.0 (hor. axis), 5.7 (vert. axis) 1064 nm
pulse width 14 ns 355 nm pulse width 14
ns LOM mass and size 43 kg, 10 cm x 42 cm x 69
cm LEU mass and size 30 kg, 13 cm x 42 cm x
69 cm
7TWiLiTE Laser Transmitter
Conceptual Optical Layout
Optical isolator
LBO doubler
LBO tripler
Power amplifier
532/1064 nm output
Fiber port
355 nm output
8HSRL/Ozone DIAL Laser Transmitter
Conceptual Optical Layout
9Power Amplifier Optical Design Modeling
Brewster Angle Slab Design Features
? 6 mm x 6 mm zigzag slab ? 2-sided diode
pumping ? 2-sided conductively cooled ? 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 Space Winds designs
Modeling predicts that extracting a power
amplifier with 25 mJ/pulse achieves 100 mJ/pulse
output at 1.3 duty cycle
10Laser Module Overview
- 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
Front View
Rear View
Purge port
1064 532 nm output window
355 nm output window
Oscillator access port
Purge port
Coolant connector
Coolant connector
Signal connectors
Power connectors
11Laser Housing DesignOscillator Compartment
Oscillator head
Resonance detection photodiode
Ring oscillator
Modulator q-switch drive electronics
Isolator
Periscope
Purge port
Coolant connection
Power connectors
12Laser Housing Design TWiLiTE Amplifier
Compartment
Amplifier
SHG
THG
Purge port
Seed laser
Coolant connection
1064/532 nm output port, external beam dump to be
added
355 nm output port, external beam expander to be
added
13Laser Housing Design HSRL/Ozone DIAL Amplifier
Compartment
Preamplifier
SHG oven
Power amplifiers
Periscope
THG oven
14Third Harmonic GenerationModeling Predictions
All modeling used SNLO from Sandia Labs ?
Assumes 100 mJ 1064 nm pump energy
? Assumes 3.5 mm pump beam diameter ?
Supergaussian coefficient 3 25 mm Type
II LBO for THG ? deff 0.521 pm/V ?
Angular sens. 3.47 mrad-cm ? Walkoff
9.49 mrad ? Temp. sens. 3.43C-cm Model
355 nm output as a function of the 532 nm
fraction of the total pump energy Results show
about 55 conversion to 532 nm optimizes the 355
nm output ? Modeling of Type I SHG in a
25 mm LBO crystal with same 1064 nm
input parameters predicts 53
SHG Model predicts that 1064 nm design output of
100 mJ in a 3.5 mm beam can be tripled to exceed
the TWiLiTE requirement of 30 mJ
Low Energy Telescopic Resonator
15Laser Electronics Unit (LEU) Overview
- Laser Module electronics
- Q-Switch Driver
- 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 Space Winds laser
transmitters
16Laser Electronics Unit Block Diagram
- Single shot hardware/firmware based interlocks
are a key design feature - Over current
- Over pulse width
- Over repetition rate
- Q-switch only when seeded
17Multi-State Software Interface Is Well Developed
18Laser Electronics UnitCavity Control
- Two component injection seeding
- 10 kHz cavity modulation and peak detection
- Detected resonances peaks provide timing
reference - Phase locked modulator drive and resonance
signals - Stabilizes resonance signal waveform and improves
frequency stability
Locked Resonance Waveform
Unlocked Resonance Waveform
19TWiLiTE Laser TransmitterBuild Status
Laser Electronics Unit
Laser Optics Module
20TWiLiTE Laser Transmitter1064 nm Beam Profile
1064 nm beam profile at THG crystal 15 W 200 Hz
21TWiLiTE Laser Transmitter355 nm Beam Profiles
At THG crystal 50 cm past
THG 100 cm past THG 130
cm past THG 2.6 mm diameter
2.3 mm diameter
2.2 mm diameter 2.2 mm
diameter Near field propagation profiles of 7.3
W, 200 Hz (36 mJ/pulse) beam
22TWiLiTE Laser Transmitter200 Hz Beam Quality Data
7.3 W 355 nm 36 mJ/pulse M2x 1.49 M2y 1.37
15 W 75 mJ/pulse 1064 nm M2x 1.23 M2y 1.15
Beam diameters after focusing lens
23TWiLiTE Laser Transmitter Summary
- Optical performance
- 15 W, M2 1.2 at 1064 nm, wall plug efficiency
of 3.1 - 7.3 W, M2 1.5 at 355 nm, wall plug efficiency
of 1.5 - 49 THG conversion efficiency
- Mass
- Laser Optics Module - 16 kg
- Laser Electronics Unit - 17 kg
- Volume
- Laser Optics Module - 31 cm x 25 cm x 14 cm
10,850 cm3 - Laser Electronics Unit 38 cm x 30 cm x 19 cm
21660 cm3 - Power
- Measured total 28 VDC power into system is 490 W
- Thermal
- Estimated total power dissipation is 475 W
- Estimated power dissipation in Laser Optics
Module is 275 W - Estimated power dissipation in Laser Electronics
Unit 200 W - Laser subsystem delivery in February 2008
24HSRL/Ozone DIAL Laser TransmitterBuild Status
Laser Optics Module
Laser Electronics Unit
25HSRL/Ozone DIAL Laser TransmitterOscillator
Performance
M2x 1.04 M2y 1.17
- Meeting lt 10 ns pulsewidth was biggest challenge
- Reducing rep rate to 150 Hz achieved 13.5 ns
- 3.7 W at 150 Hz (24 mJ/pulse)
- Low astigmatism
- M2 lt 1.2
Beam diameters after focusing lens
26HSRL/Ozone DIAL Laser Transmitter150 Hz
Preamplifier Performance
11.5 W 76 mJ/pulse 1064 nm M2x 1.15 M2y 1.14
1064 nm beam profile at preamplifier output
Beam diameters after focusing lens
27HSRL/Ozone DIAL Laser Transmitter150 Hz
Amplifier 1 Performance
1064 nm beam profile at Amplifier 1 output
28HSRL/Ozone DIAL Laser Transmitter150 Hz
Amplifier 2 Performance
1064 nm beam profile at Amplifier 2 output
29Acknowledgements
- Support for the TWiLiTE and HSRL/Ozone DIAL laser
transmitter programs was provided by NASA Goddard
Space Flight Center and NASA Langley Research
Center with funding from the Earth Science
Technology Office Instrument Incubator Program