The Lasers and Electro-Optics Branch at Goddard Space Flight Center has been tasked with building the Lasers for the Global Ecosystems Dynamics Investigation (GEDI) Lidar Mission, to be installed on the Japanese Experiment Module (JEM) on the International Space Station (ISS)1. GEDI will use three NASA-developed lasers, each coupled with a Beam Dithering Unit (BDU) to produce three sets of staggered footprints on the Earth's surface to accurately measure global biomass. We will report on the design, assembly progress, test results, and delivery process of this laser system

Blalock, Gordon

Clarke, Greg B.

Coyle, D. Barry

Frese, Erich

Hersh, Michael

Kay, Richard B.

Morey, Peter

Poulios, Demetrios

Stysley, Paul R.

NASA Technical Reports Server

Laser Production for NASA's 
Global Ecosystem Dynamics 
Investigation (GEDI) Lidar
SPIE DSS April 19, 2016
Paul R. Stysley , D. Barry Coyle, Greg B. Clarke, Erich 
Frese, Gordon Blalock, Peter Morey, Richard B. Kay, 
Demetrios Poulios, Michael Hersh
NASA-Goddard Space Flight Center 
1
https://ntrs.nasa.gov/search.jsp?R=20160005285 2019-08-31T03:22:58+00:00Z
• NASA Earth Ventures Instrument (EVI) program
• $90 M , cost capped, “PI-Led” mission
• Class C, 1-2 year mission
• Multi-beam waveform lidar
instrument with 10 ground tracks
• Launch Vehicle: 
Space-X Falcon 9/Dragon or equivalent
• Platform: International Space Station,
• Japanese Experiment Module Exposed Facility, Site: EFU#6
• Orbit: 415 km average; 51.6 degrees
• Payload Allocations (TBR): 600 Kg., 887 W, 5.4 Mbps
• Science and Mission Operations Ground System, B.32 GSFC
2
GEDI Mission Overview
2015 2016 2017 2018 2019 2020
SRR
6-15
PDR
4-16
CDR
1-17
PER
8-17
PSR
5-18
LRD
8-18
Primary Mission: 
365 Days of 
Science Collection
Extended Mission 
to Account for ISS 
Induced Downtime
3Science Goal
GEDI provides the Earth’s first comprehensive 
and high-resolution data set of ecosystem structure
C A R B O N  C Y C L E B I O D I V E R S I T Y
Characterize the effects of 
changing climate and land use on ecosystem 
structure and dynamics
• Sole GEDI observable is the lidar waveform
- Provide ground elevation, canopy height, canopy cover and various vertical 
profiles and metrics
4
Lidar Measurement
• GEDI is self-
contained laser 
altimeter
• 3 lasers produce a 
total of 10 ground 
tracks 
• Precise ranging, 
attitude & position 
sensors enable 
precise geo-location 
of each laser 
footprint (10-m 
knowledge)
• Active Pointing 
Control Mechanism 
(PCM) provides even 
distribution and 
complete coverage 
of ground tracks 
(225-m control)
5
GEDI Laser Ground Track Coverage
Canopy 
Coverage
Laser
Dense 
Canopy Laser
60 m
Canopy 
Coverage
Laser
5.4 km
600 m
1 2 3 4 5 6 7 8 9 10
6GEDI Instrument
+Z_GEDI
+Y_GEDI
+X_GEDIGPS Antenna
Star Tracker  #2
Star Tracker  #3
Star Tracker  #1
FRGF
H Fixture 
PIU
SpaceX
Passive  FSE x 4
7GEDI – Internal Views  
Pointing Control Mechanism
PIU
4X Accumulator
3X Laser
3X BDU 3X TOA
Sun Shade
Deployed Aperture Cover
Star Tracker #1 Star Tracker #3
Star Tracker #2
8GEDI Optical Bench
Star Tracker # 2
Star Tracker # 3
Star Tracker # 1
Laser # 2
Laser # 1
Laser # 3
BDU #1
BDU #2
BDU #3
TOA #3
TOA #2
TOA #1
RTA
Laser Optical Design Overview
HR
(2.5 mROC)
Risley
Pair
TCL
Nd:YAG Slab
(7x4 bar LDAs)
22 bounce
2.68 thick x 26.5o tip angle
Risley
Pair
Q-Switch
TFP1/4 WP
GRM
(-2.37 mROC)
40 cm
HR
(1.0 mROC)
Risley
Pair
TCL
Nd:YAG Slab
(7x4 bar LDAs)
22 bounce
2.68 thick x 26.5o tip angle
Risley
Pair
Q-Switch
TFP1/4 WP
GRM
(-2.37 mROC)
GEDI Pre-SRR /HOMER-2
GEDI-Laser
HR = high reflective mirror
TCL = thermal compensation lens
TFP = thin film polarizer
QS = Q-Switch
1/4 WP = 1/4 wave plate
GRM = gradient (Gaussian) reflective mirror
1. HR mirror prescription change 2.5 mCC to 1.0 mCC
2. The TCL focal length is “adjusted” for each cavity or slab 
installed, to best match thermal lensing. (TCLs ordered 
at a range anyway)
3. Mini-BX added to adjust for change in divergence
4. Reduction in output power from 17 mJ to 10 mJ to 
maintain same damage margins
5. Reduction of power allocation from 50  W to 40 W
12
9
17 mJ
10 mJ
34
5
BX
10
HOMER Class Heritage and Philosophy
Design:
-Model
-Best practices
-Margins
Bread Board:
• Confirm basic performance
• Confirm “laser physics” margins
• COTS parts
Hardened bread boards/EDUs:
• Confirm mechanical margins
• Environmental/Life Testing
ETUs:
• Flight-like procedures
• Test to flight levels
• Life testing
To FlightAny change to laser is checked for impact to 
performance and margins
HOMER Breadboard
HOMER-1
HOMER-2
GEDI Laser
11
HOMER TRL-6 Performance Summary
Titanium Flexures 
(X3)
HR
M
Sealed Enclosure w/Dual Monitoring Windows
GRM Laser HeadActive Q-Switch
Optical Bench Truss, Removable for Full
Out-of-Box Alignment
F(cyl) = -62cm Lens
Conductive Thermal Control
Flexure bonding LDA pedestal to 
optical bench
Zo
om
Single Mode Far Field Image
Dx/Dy = 0.99/0.96 mRad
Laser Settings:
• Diode Pulse = 65us 
• I = 48 A (~55% derated)
• F = 241 Hz
HR mirror Near Field Image 
Wx/Wy = 1.8/2.12 mm
Laser Output:
• E = 16 mJ
• Q-switch pulse ~11ns
• Fluence < 2.5 J/cm2
Reported 01/06/2010
Parameter HOMER Output
Energy 20 - 15 mJ
Pulse Width 12 +/- 1 ns
Rep Rate 250 -100 Hz
LDA Current 48-80 A
LDA Derating 50%
TRL 6 Mass 6 kg
Total QS Shots 
HOMER Design
15+ Billion
12
GEDI Laser Interface and Functional Overview
Telemetry
Temperature x5
Pressure x2 
QS Voltage
808 nm
~3.5 kV at 242 Hz
12 V
Trigger 
242Hz
LEU 
ISS Flow/TEC
35 +/- 2 °C
To 
BDU
~10 mJ/1064 nm
> 16 ns
0 to 50 A
40 -100 us
Trigger 242 Hz
Q-switch Driver
Laser Enclosure
Laser Optical Bench Laser Pump Module
Start 
Pulse 
Pickoff
The  Laser module consists of:
1. Laser Cavity (pump module, 
laser bench)
2. Pressurized Mechanical Housing
3. Q-Switch Drive Electronics
Mini Beam Expander
Ti Flexures 
13
GEDI Laser Mechanical Overview
GRM
Risley
Pair
¼ Waveplate
KD*P Q-Switch
Laser Head
“Bridge”
HR
Cyl Lens
Risley
Pair
Laser Diode Array
“Pedestal”
Tool Access
Optical Bench
Thin Film
Polarizer
40 cm Cavity Length from mirror to mirror
• Incorporating all opto-mechanical lessons learned from HOMER-2, LOLA, MLA, 
CALIPSO, DESDYNI, & ESA’s ALADIN
• Modular design allows complete laser assembly, alignment, and substantial 
performance without the enclosure if necessary
• Preliminary leak rate, structural, and thermal analysis performed and will be tested
20.5 ” 9.125 ”
6.25 ”
BDU Design Overview
KD*P Pockels cell mounts with 
pitch, yaw, and roll 
adjustments
Rotatable 1064nm half-wave 
plate mount
Rotatable/lockable YVO4
wedge mount
Enclosure Model
Fused SiO2 AR-coated  
windows 
BDU enclosure
Open Model
CBE Total Mass: ~1.81 kg
All optics, mounts, sensors, and seals 
(except the wedge) are either 
directly using or leveraging parts 
already being using in the HOMER 
laser
Telemetry:
IEU- Tempe x2 
LEU- Pressure x2 
LEU- QS Monitor
LEU: 12 V
Trigger 242Hz (DU)
Q-Switch Driver
3.5 kV at 242 Hz
10 mJ from Laser
Side Lobe Description Summary
X-axis
Y-axis
The image file is imported into 
a gaussian analysis model to 
integrate over the profiles, the 
quantify % energy in side lobe.  
Beam Image of Slab Exit:
A few rays at “top” of Y-axis travel a different path.  
This produces a clipping effect, or “lobe” at the 
slab output end.
This creates problems for science differentiating 
between sloped ground and tree height.
To remove this you can either:
1) Clip off the side lobes outside the cavity
2) Make the beam smaller 
3) Make the slab bigger
All options were explored and GEDI selected 
option 2 by changing HR Mirror curvature.  
Options were reviewed externally by NESC supervised 
laser team from 554, 562, and expert from NGS.
See GEDI-LAS-REVW-0004
Side lobes
Laser Testing Performance Summary 
Parameter Value Unit
Average
Energy
10.2 mJ
Frequency 242 Hz
Pump Width 71-77 μs
Current 55 A
1000m470m
Inspection Point
2000m
Calibration Point
470m330m 700m 1000m
220m
3200m2700m
LDA 
Turned 
Up
3200m
HOMER-1 1 mCC HRM Life Assessment Testing
No additional damage found
HOMER-1 sensitive to temperature
10 mJ example beam with 
no side lobes from GEDI-
LAS-RPT-0029
Parametric Testing :
• Thermal lensing
• Diode distance
• End mirror tolerance
ETU Diode Life Test Results
Energy measurements were corrected for the LDA temperature change. Efficiency of the LDA decreases as the temperature increases.
Voltage drop change
Took diodes off for 1B Shot inspection and DPA
Voltage drop correction
Diodes re-inpsected several times thru testing. No 
damage or unexpected change in performance
18
Cavity Fluence Estimates
HR
Risley
Pair
TCL
Nd:YAG Slab
Risley
Pair
QS
TFP
1/4 WP
GRM
… To get the operational damage 
margin for each optic: 
MD =jLIDT /jcalc
HR Risley
Pair
TCL Slab 
Face
Slab TIR Slab 
Face
TFP QS ¼ 
WP
Risley
Pair
GRM
Meas LIDT 
(J/cm2)
11.5 44 25 >10 12* >10 20 >10 >10 44 4
Calc Fluence
(J/cm2)
1.75 1.95 2.08 2.37
(1/2.23)
2.37*
(1/1.56)
2.37
(1/2.23)
2.22 2.69 2.85 3.06 3.24
Margin MD 4.2 22.6 15.3 >9.4 6.1* >9.4 9.0 >3.7 >3.5 14.4 1.23
Sigma 0.32 0.36 0.37 <0.43 0.43* <0.43 0.4 0.48 0.51 0.55 0.58
jLIDT
jcalc
RGRM =
1
pa2
× R0 ×
0
a
ò0
2p
ò exp
-2r2
w 2
é
ë
ê
ù
û
ú ×r ×dr ×dq
Ein = Eout ×
(1+ RGRM )
(1- RGRM )
Energy (avg) Inside laser cavity with output 
coupler reflectivity ROC= RGRM: 
But our reflectivity changes with beam size 
on the GRM, so we have to estimate:
jcalc = Ein ×
2
p ×w calc
2
So we can calculate 
the fluence on each 
optic:
*worst case:
round beam 
at GRM-end 
of slab
GEDI Laser Requirements Verification
ID Requirement Values FT CPT Life test Technique Used
1 Laser Wavelength
1064.5 nm ± 0.2 nm 
in vacuum
x O
Pickoff beam. Use built in software to calibrate measurement 
for vac.  Take vacuum and air values
2* Laser Output Energy
10 mJ +5% fully 
captured beam at the 
output 
x x C
Measuring Total Output Energy using energy meter with 10ms 
integration time. 
CPT - energy meter put at the end of the snout to get full 
output. Used to calibrate pickoff measurement as well
FT/Lifetest - calibrated pickoff
3*
Far-Field Divergence 
of the Central Lobe
0.6 mrad ±0.08mrad
1/e2 div. x x C
Spiricon camera (raw beam data) 5-10 captures
Computer Analysis and post processing for side lobes   
FT-50 cm lens
CPT - Rayleigh Range
6
Laser Output 
Polarization Ratio
≥ 200:1 x O
Measure by hand using wave-plate/hi ratio polarizer 
configuration
9 Pulse Repetition Rate 242 ± 2 Hz x x C
Confirm pulse with Tektonix 2024C and use e-drive output 
reading for continuous measurement 
10 Pulse Width
<16ns
ns Full-width and half-
max
x x C
FT- 200 MHz Oscilloscope Average of 16 captures of laser pulses
CPT -2 GHz scope. High speed Oscilloscope compiling 10,000 
shots with histogram through computer analysis and post 
processing. LMB will be measured as well. 
12
Laser Pulse Energy 
Concentration in Far-
Field Outside of 
Central Lobe
≤ 0.5% of 1/e2 Central 
Lobe per energy 
concentration
x O
Spiricon camera (raw beam data) 5-10 captures
Computer Analysis and post processing   
13*
Number of Laser 
Shots for Life Testing
3.2 billion shots x x C
GSE shot counter will monitor shots for every test.  ETU life time 
shot count will be monitored continuously 
24
LDA Operating
Temperature 
35 +/- 2 °C x C .Internal 10k thermistors read by EGSE
O = Occasional 
C = Continuous 
X = One Time 
Measurement 
19
GEDI Laser Test Matrix GEDI-SYS-PLAN-0019
• Environmental Testing performed on ETU and Flight units
- ETU: Vibration, TVAC, EMC, and life test
- Flight: Vibration, TVAC, EMI/C (at instrument level)
- CPTs before and after each test (or specific cycles)
• Interface testing: BDU, LEU, DOE 
20
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Laser GSE Functional Diagram
Optical Setup – Laser Lifetest w/BDU
ETU Laser Development Flow
GSE
Optical Parts 
Procurement
Start 
Build
Acceptance 
Testing
Bonding
Kitting & 
Inspection
Preparation 1/16 Sub-Assembly 3/16 
Pump 
Module
Optical 
Bench
Enclosure
Integrate Pump 
Module and 
Optical Bench
Integrate 
Electronics
Test Cavity 
Performance
Integrate 
Enclosure
CPT
LEGEND
Parts Ordered Parts Delivered
Paperwork Release Complete Task
Complete
Monitor - no tech/cost/schd impact
Monitor - tech/cost/schd impact
On Plan
Laser Module 
Assembly 4/16
TRR
Vibration/CP
T
Environmental 
Testing 5/16
EMC
TVAC/CPT
Start Life 
Testing 5/16
Mechanical 
Fabrication
Electrical
Harnessing
SLAC 
Repair
Interface 
Test
Special 
Testing*
*Special testing includes pressure and  temperature cycling 
Pre-Qual 1/16
Q-switch
Spare 
Enclosure 
Seal Test
Q-switch 
Driver
23
Laser Assembly Flow
Assemble bucket:
• Flexures
• QSD
• Harness
Workmanship Test Seals 
(Qualify on ETU)
Add Pump Module:
• Safe-to-mate GSE
• Test Fire Diodes
24
25
Laser Assembly Flow
Functional Test:
LASER-2,3,9,10,11
Comprehensive Performance 
Test:
LASER-
1,2,3,4,5,6,7,8,9,10,11,12,15,1
8,19,20,21
Special Test:
• Lab Pressure Test
• FT  min/nom/max pressure
Special Test:
• Lab Temp Cycle
• FT  every 0.5 C
Add Laser Optical Bench & 
Bench Optics
Seal Enclosure 
Special Test:
• Lab Temp Cycle
• FT  every 0.5 C
Environmental
& Interface 
Testing
Laser ETU Bucket and Driver Assembly 
“Bucket” Enclosure
Q-switch Driver
Titanium Flexure 
26
Laser ETU Diode and Bench Assembly
Laser Diodes Laser Optical Bench
27
28
BDU ETU Assembly Test Configuration
Q-switches
Crystal
Functional Test Platform
TVAC Testing


Laser Pulse Production for NASA's Global Ecosystem Dynamics Investigation (GEDI) Lidar

Laser Pulse Production for NASA's Global Ecosystem Dynamics Investigation (GEDI) Lidar

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