1. Laser Transmitter for the Tropospheric Wind Lidar Technology Experiment (TWiLiTE) Floyd Hovis, Fibertek, Inc. Bruce Gentry, NASA Goddard Space Flight Center

2. Laser Transmitter Specifications
Performance Specifications/Design Performance Summary Table
Parameter
Specification
Design Performance
Margin
Wavelength
355 nm NA
Laser Energy (UV)
>30 mJ
40 1.3% duty cycle
> 33%
Pulse Rep Rate
200 Hz
Average Power
> 6 W
8 1.3% duty cycle
Beam Quality, M^2
< 3
< 2.5
17%
Energy in the Bucket
> 86% encircled energy into 3x d. l. beam
Meet specification
TBD
Frequency Stability
< 5MHz RMS for 30 sec
< 50 MHz RMS for 30 min
< 30 MHz RMS for 30 min
40%
Seeding Efficiency
>99.9%
>99.9
Meets spec
Pulsewidth
> 15 ns
~13-15 ns
None
Linewidth
< nm
~120 MHz
Pointing stability
< 10% of beam divergence
Electrical Power (excl. chiller)
550 W
470 W
14%
Thermal Management
Conductive or Liquid Cooled
Conductive to Liquid
Lifetime
1 billion shots (75% diode 1064 nm
1 billion 1064 nm

3. Environmental Design Performance
Environmental Design Parameters - Laser Optics Module
Parameter
Operating range
Survival range
Ambient temperature (°C)
10 to 40*
-30 to +50
Ambient pressure (mbar)
0 to 1050
*Assumes thermal interface plate maintained at nominal operating temperature +/-2°C
Environmental Design Parameters - Laser Electronics Unit
Parameter
Operating range
Survival range
Ambient temperature (°C)
0 to 50*
-30 to +50
Ambient pressure (mbar)
35 to 1050
0 to 1050
*Assumes liquid cooled interface plate for low pressure operation
Design performance exceeds all environmental performance specifications

4. BalloonWinds, Raytheon, and Air Force Lasers Provided Basis For Key Design Features
Three amplifier design
Autonomous operation controlled through RS232 serial interface
Nominal 28 VDC primary power
Space-qualifiable electrical design
Thermal control through conductive cooling to liquid cooled plates bolted to bottom of laser module
355 nm single frequency output of > Hz (23 W)
Deliverable system will undergo extended life testing at Raytheon
Electronics module
Laser module
Space-Winds Lidar Laser Transmitter
Final acceptance testing was completed in November 2006

5. Conceptual Optical Layout
Laser Transmitter
Conceptual Optical Layout
Ring Resonator
Fiber-coupled
1 mm seed laser
Optical isolator
LBO
doubler
LBO
tripler
Power amplifier
532/1064 nm
output
Fiber
port
355 nm
output

6. 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

7. Laser Housing Baseline Design Oscillator Compartment
Ring Resonator
Purge port
355 nm nm output window
Coolant connection
1064 & 532 nm output window

8. Laser Housing Baseline Design Amplifier Compartment
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

9. 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

10. 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 ms
Repetition rate 200 Hz
Pump Energy J
Heat Dissipation 250 watts
Slab Size 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 ns
Output Beam Size ~3 mm super gaussian (variable)

11. 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

12. Third Harmonic Generation Results Of Fibertek IR&D
 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)
Type I
LBO doubler
355 nm
output
Type II
LBO tripler
1064 nm
input
1064nm

13. 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

14. Electronics Overview Laser Module electronics Laser Electronics Unit
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
The Laser Unit is an enclosed canister containing the optical assemblies and laser bench, the laser diode heads, and the indicated electrical elements. It will likely be sealed with a slight overpressure internally, and use hermetic circular connectors for electrical interconnections.
For the prototype laser system, the Electronics Unit will be a rack-mounted unit, consisting of several electrical assemblies interconnected inside an overall enclosure. For a flight unit, this enclosure need not be sealed, but the packaging of unit needs to be optimized for the specific available volume and footprint, and also for the best transfer of thermal loads to the radiator surface.

15. Software Interface Is Complete
COLD 1
WARMUP 2
FAULT 3
HPWR 6
LPWR 5
DIAG 7
ARMED 4
Power-up
CNTRL INITIALIZE
CNTRL LASERDISARM
CNTRL HTRSON
CNTRL CLRINT
CNTRL LASERARM
CNTRL LPWRMODE
CNTRL HPWRMODE
CNTRL DIAGMODE
CNTRL STOP
Any active
fault
“1”
“4”
“-” (hyphen)
“D”
“7”
“2”
“8”
“C”
“A”
Blue text indicates alternative command characters
when operating laser system from HyperTerminal serial interface

16. 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

17. 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
For testing purposes, most system parameters that are fixed during normal operation will be implemented as programmable parameters. These parameters will be optimized during testing, and then made fixed for the final deliverable system.
Parameters that are adjustable will in general be accessible through the serial communications interface. A command protocol will be developed that will provide a set of commands for commanding the laser operating modes, gathering important measurement and performance data from the laser, and adjusting a selected set of operating parameters.
Other command functions that can be included are: hardware serial numbers, software version ID, self-test functions, and ground-test functions (low-power mode, reprogrammability of FPGA or software, watchdog enable/disable, etc.).

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