A proposed 1 micron eyesafe Lidar system for global spacebased Remote Wind Measurements'

1
A proposed 1 micron eyesafe Lidar system for
global space-based Remote Wind Measurements.
Robert L. Byer Applied Physics Stanford
University Arun Sridharan Lawrence Livermore
National Laboratory
14th CLRC July 8-13, 2007 Snowmass Village,
Colorado
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Contents
Early History and Concepts
Remote Sensing with Lasers Atmospheric Remote
Sensing Unstable Resonator - 1J Nd YAG 1.4
4.3 micron Tunable OPO Global Wind
Sensing LD pumped NdYAG Frequency
Stabilization Coherent Laser Radar at 1064nm
Future Directions Improvements in Lasers Arun
Sridharan thesis Slab Lasers and YbYAG slab
amplifiers for wind sensing OPAs for 1.5
micron generation Global wind sensing
eyesafe Rethinking what is eyesafe A
possible way forward
3
Atmospheric Remote Sensing
Motivation for tunable lasers at Stanford
Atmospheric Remote sensing beginning in
1971 Unstable resonator NdYAG -- Quanta Ray
Laser 1.4 - 4.4 micron tunable LiNbO3 OPO --
computer controlled Remote sensing of CH4, SO2
and H2O and temperature
Early Remote Sensing 1960 - 1978 LIDAR Laser
Detection and Ranging Inaba, Kobayashi Detection
of Molecules Kidal and Byer Comparison of
Detection Methods DIAL Differential Absorption
Lidar Menzies CO2 laser Direct and Coherent
Detection Walther Rothe Remote sensing of
pollutants Svanberg Remote sensing van for
pollution monitoring Huffaker Global Wind
Monitoring proposed
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Monitoring Air Pollution
Helge Kildal and R. L. Byer Comparison of Laser
Methods for The Remote Detection of
Atmospheric Pollutants Proc. IEEE 59,1644 1971
(invited)
A shoe box of postcards requesting
reprints Informed us that the paper had been read!
Henningsen, Garbuny and Byer - 1974 Vibrational-R
otational overtone spectrum of Carbon Monoxide by
tunable OPO. (Chromatix NdYAG pumped LiNbO3
OPO Product introduced as product in 1969)
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Atmospheric Remote Sensing
Motivation for tunable lasers at Stanford
Atmospheric Remote sensing beginning in
1971 Unstable resonator NdYAG -- Quanta Ray
Laser 1.4 - 4.4 micron tunable LiNbO3 OPO --
computer controlled Remote sensing of CH4, SO2
and H2O and temperature
Sune Svanberg
Early Remote Sensing 1960 - 1975 LIDAR Laser
Detection and Ranging Inaba, Kobayashi Detection
of Molecules Kidal and Byer Comparison of
Detection Methods DIAL Differential Absorption
Lidar Menzies CO2 laser Direct and Coherent
Detection Walther Rothe Remote sensing of
pollutants Svanberg Remote sensing pollution
monitoring Huffaker Global Wind Monitoring
proposed
Humio Inaba
Herbert Walther
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Unstable Resonator Concept - 1965
A. E. Siegman Unstable optical resonators for
laser applications Proc. IEEE 53, 277-287, 1965
R. L. Herbst, H. Komine, R. L. Byer A 200mJ
unstable resonator NdYAG Oscillator Optics
Commun. 21, 5, 1977
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Unstable Resonator NdYAG Oscillator
R. L. Herbst, H. Komine, and R. L. Byer A 200mJ
Unstable Resonator NdYAG Oscillator Opt.
Commun. 21, 5, 1977
gt 10,000 Quanta Ray Lasers sold by 1995
Quanta Ray 532nm output after SHG in KDP
crystal. Note hole in beam.
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1.4 to 4.3 micron Computer Tuned LiNbO3
OPO(PDP-11 8k core memory 2Mb disk)
Stephen J. Brosnan, R. L. Byer Optical
Parametric Oscillator Threshold and Linewidth
Studies Proc. IEEE J. Quant. Electr.
QE-15,415,1979
Steve Brosnan observing atmospheric spectrum with
OPO tuning under PDP-11 computer control
Fig 19. LiNbO3 OPO Angle Tuning curve ( 45-50
deg) 1.4 4.3 microns
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Remote Sensing of SO2, CH4, Temp and Humidity
R. A. Baumgartner, R. L. Byer IR Lidar with
remote measurements Of SO2 and CH4 Applied
Optics 17, 3555,1978
Martin Endemann, R. L. Byer Remote Measurements
of Temperature and Humidity using a tunable IR
Lidar Applied Optics 20,3211,1981
4 hours of Continuous data March 11, 1980
Temp
Humidity
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Remote Sensing Telescope at Stanford - 1980
Atmospheric Remote Sensing using a NdYAG Pumped
LiNbO3 Tunable IR OPO. The OPO was tuned
under Computer control continuously From 1.4 to
4.3 microns Atmospheric measurements Were made
of CO2, SO2, CH4, H2O and Temperature.
Sixteen inch diameter telescope on the roof of
the Ginzton Laboratory
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The big picture Remote sensingTunable laser
needed
Quanta Ray Unstable Resonator NdYAG lasers first
sold in 1974 was later extended to pump the BBO
parametric oscillator tunable Source by Spectra
Physics in 1994. To date more than 10,000
Quanta Ray laser systems have been sold many of
which are used for remote Sensing applications
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Contents
Early History and Concepts
Remote Sensing with Lasers Atmospheric Remote
Sensing Unstable Resonator - 1J Nd YAG 1.4
4.3 micron Tunable OPO Global Wind Sensing
The Huffaker Challenge LD pumped Solid State
Lasers Frequency Stabilization the
NPRO Coherent Laser Radar at 1064nm
Future Directions Improvements in
Lasers Slab Lasers and YbYAG slab amplifiers
for wind sensing OPAs for 1.5 micron
generation Global wind sensing
eyesafe Rethinking what is eyesafe A
possible way forward
13
Global Wind Concept - Huffaker
Global wind sensing
Milton Huffaker proposed coherent detection of
wind using eye-safe lasers. Applied Optics 22
1984
Founded Coherent Technologies In 1984 same year
as Lightwave
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Global Wind Sensing
Dont undertake a project unless it is
manifestly important and nearly impossible.
Edwin Land - 1982
Remote Sensing with Lasers Atmospheric Remote
Sensing Quanta Ray 1J YAG and OPO Global
Wind Sensing The Huffaker Challenge LD
pumped Solid State Lasers Frequency
Stabilization the NPRO Coherent Laser Radar
R. M. Huffaker, editor, Feasibility Study of
Satellite-Borne Lidar Global Wind Monitoring
System, NOAA Technical Memorandum ERL, WPL-37,
1978
R. M. Huffaker and R. M. Hardesty Remote sensing
of atmospheric Wind velocities using solid-state
and CO2 coherent laser systems Proc of the IEEE
84(2) 181-204, 1996
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Laser Remote Sensing CRC Press 2005
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Laser Requirements for Global Wind Sensing
Global Wind Sensing 400 km orbit 1 meter
diameter telescope Backscatter from dust in
atmosphere (10-9)
Laser Source Requirements 5 J at 20 Hz or 100 W
average power (CO2 Laser) lt1MHz linewidth, 1
microsecond pulse duration 10 electrical
efficiency gt30,000 hours of operation Eye-Safe
output wavelength gt1.5 microns
In 1983 initiated research to meet the laser
source requirements led to the Diode Pumped
NdYAG in 1984
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Diode Pumped Solid State Laser - 1964
Keyes Quist - 1964 Schematic of the first
diode-pumped solid state laser. The laser used
five GaAs diode lasers to pump the U-doped CaF2
laser rod that was 3mm in diameter and 4cm long.
The laser mirrors were coated directly onto the
rod.
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Diode Pumped Solid State Lasers - 1984
Laser Diode Pumped NdYAG - 1985 Binkun Zhou,
Tom Kane, Jeff Dixon and R. L. Byer Efficient,
frequency-stable laser-diode-pumped NdYAG
laser Opt. Lett. 10, 62, 1985
5mm NdYAG Monolithic Oscillator 2mW output power
for 8mw Pump 25 slope efficiency
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Proceedings of NASA Sponsored Workshop pub 1985
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Remote Sensing and Solid State Lasers
workshop at Stanford - Oct 1-3, 1984
R. Curran, Frank Allario Bob Menzies Ed
Browell A Rosenberg Tom Wilkerson W. H. Fuller C.
Korb Jack Bufton C. S. Gardner Don Scifres John
Walling Lyn Mollenauer Norman Barnes Chuck
Byvek Tom Kane Bill Krupke
NASA Remote Sensing
Laser Sources and Nonlinear conversion
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Progress in Laser Diodes - 1978
Don Scifres, Ralph Burnham, and Bill Streifer -
1978 One Watt Laser Diode Bar with 25
electrical efficiency. This was the first Watt
level power output from a linear Laser Diode
Array. Within one decade the output power would
increase to greater than 100W from a one
centimeter LD bar.
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NdYAG NdGlass Slab Geometry Lasers - 1972
The zig-zag slab laser concept Cancels thermal
focusing to first order Power scales as slab
area Retains linear polarization
Zig-Zag face pumped Slab laser
Active mirror or also known as the thin disk
laser.
Joe Chernoch Invention Patent 3,679,999 July
25, 1972
Disk amplifier geometry adopted for the
NIF Laser
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The Slab Geometry Laser - Theory 1984
Slab Geometry Laser - Theory Power scaling
(L X W)/t Cooled Area/thickness
(stress fracture limit) Thermal lensing -
zig-zag path averages first order
thermal lens Thermal Birefringence one
dimensional cooling eliminates
birefringence Rod Geometry Laser Power scaling
length (independent of rod or fiber
diameter) Thermal Lensing Birefringence
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NdYAG Coherent Laser Radar
Coherent Laser Radar Local Oscillator Inventio
n of the Nonplanar Ring Oscillator Power
Amplifier Multipass 60 dB gain slab
amplifier Heterodyne Receiver Fiber coupled
heterodyne detection
Goal wind sensing from the laboratory using a
coherent NdYAG laser transmitter-receiver
Long term goal Transmitter for Global Wind
Sensing
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The Non-Planar Ring Oscillator - 1984
Tom Kane, R. L. Byer Monolithic, unidirectional
Single-mode NdYAG ring laser Opt. Lett.
10,65,1985
NonPlanar Ring Oscillator Single frequency
lt10kHz
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NPRO Patent issued March 25, 1986
Patent ran its full 17 years on March 25, 2003
Lightwave celebrated a very successful product
that is still on the market today including
harmonic conversion to the green and UV.
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Tom Kane 2W of Blue from fiber laserLightwave
Electronics 2004
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The 60 dB Multipass Slab amplifier
T. J. Kane, W. J. Kozlovsky, R. L. Byer 62 dB
gain multipass slab geometry NdYAG Amplifier Opti
c Lett. 11, 216, 1986
Coherent laser radar at 1.06 microns Using
NdYAG lasers Optic Lett. 12, 239, 1987
We elected to not patent the angular
multiplexed Slab amplifier we could not foresee
a market for the device. (big mistake!)
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Art Schawlow Prediction--1979
An aside just for fun!
Art Schawlow with Mickey Mouse Balloon and a
Ruby Laser
New Frontiers for Ubiquitous IT Services NTT
Atsugi RD Center, May 26-27, 2003
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Iodine Stabilized NdYAG Master Oscillator
Ady Arie, Stephan Schiller, Eric Gustafson R. L.
Byer Absolute Frequency Stabilization to
Hyperfine Transitions in Molecular Iodine Opt.
Lett. 17, 11, 1992
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Molecular Iodine Optical Clock
Jun Ye, Long Sheng Ma, and John L.
Hall Molecular Iodine Clock Phys Rev Lett 87,
Dec 2001
Stability 5 x 10-14 at 1 sec Comb precision
over octave from 532nm to 1064nm is 3.5 x
10-15 Comb standard deviation over a Period of
one-month 6 x 10-14 Can be improved by a factor
of 10
Glimpse to the future
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Noble Prize Winners 2005Roy Glauber, Ted Hansch,
John Hall
Roy J. Glauber
Theodor W. Hänsch
John L. Hall
Robert L. Byer
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Coherent Laser Radar at 1.064 microns
Optics Letts 12 pg 239 April 1987
A nice demonstration of capability. However,
still left the challenge - How to meet the
Global Wind Transmitter requirements?
However, I met with J. Hall at JILA in 1988 to
discuss frequency stabilization of solid state
lasers
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LISA Concept
Peter Bender holding 4x4cm Au/Pt cube
Schematic of LISA in 1988 Expected
Launch date of 1998 (now 2015) Laser power
1W Laser stability extremely high Laser
reliability gt 5 years
Gravitational waves open a new window on
universe Detect amplitude and phase of
gravitational waves with sensitivity to detect
back the era of galaxy formation.
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LISA Mission
LISA - Laser Interferometer Space Antenna Phase
A Study - 1995 Joint mission NASA and ESA 3
satellites in solar orbit 1 W laser - NdYAG
NPRO 5 million km interferometer path 30 light
seconds round trip delay Scheduled for launch in
2015 1 year to station, 5 year mission Will
detect binaries in our galaxy Will detect massive
Black Holes at Cores of most galaxies
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Lasers for the LIGO interferometer
Laser Characteristics Wavelength 1064 nm TEM00
output power gt 10 W Non-TEM00 power lt 2
W Intensity noise dP(f)/P lt 3 x 10-8 150 Hz
lt f lt 10 kHz
Test masses
Fabry
-
Perot
Mode
Cleaner
Beam
Splitter
Conditioning
Optics
NdYAG Laser
Amplifier
Power Recycling
Photodetector
Mirror
Strain sensitivity 10-22
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10 Watt NdYAG MOPA - LIGO
LIGO Prestabilized Laser 10 W TEMoo mode
NdYAG NPRO Master Oscillator Followed by
Power Amplifier
LIGO Laser installed in Summer Of 1995. Diode
pumped NdYAG has Shown high reliability and
capability for Power scaling in the future.
It is plausible for LIGO to detect Gravitational
waves but not likely. Advanced LIGO will improve
sensitivity By a factor of 10 and the event rate
by 103
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LIGO and LISA Gravitational Waves
One Thing leads to another Bradford
Parkinson, inventor GPS
Scientific Applications of Lasers Global Wind
Sensing LD pumped NdYAG Frequency
Stabilization LIGO and LISA Gravitational
Waves 10 W NdYAG MOPA for LIGO 200W
NdYAG Slab MOPA Adv LIGO 1 W Iodine
Stabilized NdYAG LISA 300W Green Laser Adv
LISA
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Contents
Early History and Concepts
Remote Sensing with Lasers Atmospheric Remote
Sensing Unstable Resonator - 1J Nd YAG 1.4
4.3 micron Tunable OPO Global Wind Sensing
The Huffaker Challenge LD pumped Solid State
Lasers Frequency Stabilization the
NPRO Coherent Laser Radar at 1064nm
Future Directions Improvements in Lasers Arun
Sridharan thesis Slab Lasers and YbYAG slab
amplifiers for wind sensing OPAs for 1.5
micron generation Global wind sensing
eyesafe Rethinking what is eyesafe A
possible way forward
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A YbYAG master oscillator power amplifier and
PPLN optical parametric amplifiers for remote
wind sensing
Arun Kumar Sridharan E.L. Ginzton Laboratory
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Byer Laser Group
Dr. Arun Kumar Sridharan
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1978
1970
1994
1994
2006
CALIPSO
2012
Graphic courtesy Ed Browel NASA
43
YbYAG Slab- OPA approach for global wind
transmitter
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YbYAG slab amplifier
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Limits to gain and energy storage

• Single pass amplification of spontaneous
• emission depletes the population inversion
• and is the fundamental limit to gain and
• stored energy.

Closed loop ASE paths that have more gain than
loss deplete the population inversion and hence
the gain below the ASE limit.
Reflectivity of all surfaces for the ASE needs to
be reduced to prevent loss of stored energy.
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Reasons for extraction of energy in microsecond
pulses

• Transform limited 1 MHz line-width, required for
  1 m/s global wind velocity resolution.

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Amplifier design considerations

• Nearly complete absorption of pump light. Pump
  is confined in crystal by TIR on the 4 large
  surfaces.
• Better signal to pump mode overlap gt Higher
  gain efficiency
• Uniform gain across beam gt better mode quality

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Preamplifier Slab properties
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Slab batch fabrication process
Yb

• Improves the quality of zig-zag slabs (because
  fabrication steps involve working with large
  surface areas).
• Significantly reduces the cost of zig-zag slabs

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Parasitic suppression applied to edges increases
gain
2.5 x
Slab with cladding for parasitic suppression
on TIR edge faces

• Edge cladding leads to 2.5 x increase in gain
  and stored energy

• The small signal gain is approaching the ASE
  limited gain of 3-4

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YbYAG pre-amplifier double-pass experiment
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Scaling of pre-amplifier to 1 J level
15.6 J/cm3 of demonstrated stored energy density
allows calculation slab dimensions needed for
scaling.
100 mJ/ms amplifier _at_ 40 Hz
3 YbYAG Slab dimensions 1.1 mm x 1.1 mm
x 18 mm Volume 0.015 cm3 Peak Pump
Power (4 duty cycle) 1130 W Stored Energy
280 mJ Heat Extracted 12.6 W/cm2
1 J/ms amplifier _at_ 40 Hz
1.3 YbYAG Slab dimensions 3.5 mm x 3.5
mm x 38 mm Volume 0.45 cm3 Peak
Pump Power (4 duty cycle) 11500 W Stored
Energy 2.9 J Heat Extracted 17.9 W/cm2
We keep large (gt 121) aspect ratios to minimize
transverse gain
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Goal High pulse energy 1.55 mm radiation via OPA

• Built a 100 mJ NdYAG MOPA
• Waveguide PPLN OPA
• Bulk PPLN OPA

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Bulk PPLN OPAExperiment
Input signal energy 1 mW cw
or (1 nJ/ms)

• We achieved 63 dB gain without parasitics by AR
  coating and angle polishing
• faces of crystal. Output energy is consistent
  with 2-D gaussian model.

• 2 mJ output can be achieved in 3-4 cm PPLN
  device by using the waveguide
• OPA output as the signal input.

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Contents
Early History and Concepts
Remote Sensing with Lasers
Future Directions Improvements in
Lasers Slab Lasers and YbYAG slab amplifiers
for wind sensing OPAs for 1.5 micron
generation Global wind sensing
eyesafe Rethinking what is eyesafe A
possible way forward
Keep it simple straightforward and elegant
56
Contents
Early History and Concepts
Remote Sensing with Lasers
Future Directions Improvements in
Lasers Diode pumped solid state lasers Slab
Lasers and YbYAG slab amplifiers for wind
sensing OPAs for 1.5 micron generation Globa
l wind sensing eyesafe Rethinking what
is eyesafe A possible way forward
Is it possible to Manage pulse energy, average
power, and pulse transmission to operate a Global
Wind Sensing mission at 1030nm and be eyesafe?
Keep it simple straightforward and elegant
57
Adaptive Optics for Astronomy20W cw NdYAG
sodium yellow on the sky - 2002
Adaptive Optics is leading to the next revolution
in astronomy. The Laser Guide Star is an
essential element for AO on the current 10m
class telescopes, and for
the AO control of the planned Next Generation 30
meter diameter telescopes.
Sodium yellow at the Star Fire Optical Range,
Albuquerque, NM Photo courtesy Bob Fugate
Craig Denman - AFRL
50 W cw NdYAG yellow on the sky 2005
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Considerations for eye-safe operation
Maximum permissible fluence limit for ground
observers at 1 mm is 5 mJ/cm2

• The key idea is to operate a lidar design such
  that it meets eye-safe limits.
• 85 of earths surface has negligible human
  population. Can selective reduction of pulse
  energy over populated areas enable eye-safe
  operation?
• Can S/N be maintained by increasing repetition
  rate and average power over the 15 of the globe
  where populations density is high?

The Laser Guide Star system is operated to avoid
illumination of aircraft and overhead spacecraft.
59
Satellite trajectory and graphical representation
of NASA/NOAA wind velocity measurement
specifications
Key question Is eye-safe operation attainable
with a 1 mm transmitter ?
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Our design uses Frehlichs model for velocity
error estimation
Start with LIDAR Equation and use Frehlichs for
required pulse energy
Average number of coherently detected
photo-electrons per observation time for each
shot
Number of independent samples of return signal
per observation time
M Number of complex samples per range gate for
each shot N Number of lidar shots per wind
measurement for each resolution cell

• These four parameters are used as inputs to
  Frehlichs statistical model that is based on
  simulated wind field data. The model predicts
  error in velocity estimate, sg, and b, a
  figure-of-merit of lidar performance.

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1030nm YbYAG Coherent Lidar design parameters
62
Illustrates tradeoffs between transmitted pulse
energy and repetition rate for equivalent lidar
performance
Maximum permissible fluence limit for ground
observers is 5 mJ/cm2
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Our approach for global wind transmitter 1.03 mm
MOPA
0.1 W cw 1.03 mm laser
0.1 µJ
fiber pre-amplifier
5 mJ
Acousto-Optic Modulator
Slab power amplifier
50-100 mJ
100 mJ
YbYAG slab pre-amplifier

• Scalable
• Power available despite element failure
• No complex electronics required
• Efficiency improves with saturation in the
• power amplifier.

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Laser Requirements for Global Wind Sensing
Global Wind Sensing 400 km orbit 2 meter
diameter telescope Backscatter from dust in
atmosphere (10-9)
Laser Source Requirements 5 J at 20 Hz or 100 W
average power (CO2) 54 mJ 30Hz or 2W
average power (YAG) 10 kHz linewidth, 1
microsecond pulse duration 10 electrical
efficiency gt30,000 hours of operation Eye-Safe
output wavelength gt1.5 microns Eye-Safe
operation by managed pulse transmission
After 30 years the nearly impossible and very
important monitoring of Global Wind maybe
possible using eyesafe operation at 1 micron.
65
Winds The final frontier?
2015 NASA Coherent Wind Sensor
2007 ESA Wind mission
Adapted from M. Kavayas slides
66
Extra slides

• The slides following this slide are contain
  information that were not part of the talk but
  could be used to answer basic questions.

67
Basic principles of LIDAR
Light Detection And Ranging
68
(No Transcript)
69
Required precision of velocity estimates leads
to derivation of transmitter properties
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Backscatter radiation from wind is shifted in
frequency
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Laser Requirements for Global Wind Sensing
Global Wind Sensing 400 km orbit 1 meter
diameter telescope Backscatter from dust in
atmosphere (10-9)
Laser Source Requirements 2 J at 20 Hz or 40 W
average power 10 kHz linewidth, 1 microsecond
pulse duration 10 electrical
efficiency gt30,000 hours of operation Eye-Saf
e output wavelength gt1.5 microns
nearly impossible and important. Began to work
on laser source in 1980. Led to Diode
pumping and Coherent Laser Radar using NdYAG.
72
YbYAG Slab OPA - 1.55 mm Laser Transmitter
System
73
Energy extraction considerations
74
Bulk PPLN OPA Modeling
Plane wave OPA model
2-D Gaussian wave OPA model
2D model enables choice of transverse mode shapes
and sizes and crystal length for optimum
conversion while avoiding back conversion.
75
Scaling of the OPA
150 mJ, 1.55 mm, ms pulses with 1 J pump energy
Target
Fabricate 3-4 mm thick crystals to avoid surface
damage
Need
Solution Stoichiometric PPLN and PPLT, or
MgOPPLN,
Key Properties
Enables poling of 3-4 mm devices
1. Low coercive electric field
Photorefractive damage threshold increased
Room temperature operation possible
2. Low defect concentration
3. Significantly reduced Green Induced IR
Absorption (GRIIRA)

• To further improve conversion efficiency,
  higher-order or
• top-hat gaussian beams can be used.

76
Accomplishments

• Performed a point design and derived laser
  transmitter requirements
• for a space-based LIDAR system at 1.55 mm.

77
NASA/NOAA Global Wind Measurement SpecificationsI
78
NASA/NOAA Global Wind Measurement
SpecificationsII
Measurements must be made with eye-safety for
ground observers
79
Quanta-Ray LaserTunable OPO
Richard Baumgartner
Bob Byer
Studies of LiNbO3 OPOs and OPAs for remote
sensing of SO2 and CH4 in the Atmosphere.
New Frontiers for Ubiquitous IT Services NTT
Atsugi RD Center, May 26-27, 2003
80
Diode pumped Slab Lasers
TRW DAPKL NdYAG Laser (1988 -
1993) Three stage MOPA with Phase Conjugation 1
kW near diffraction limited laser Followed by SHG
to green (10 J Q-switched pulses at 100
Hz Diode Array Pumped Kilowatt Laser
R. J. Shine, A. J. Alfrey, R. L. Byer 40W cw,
TEMoo-mode, Diode-laser-pumped, NdYAG
miniature Slab laser Opt. Lett. 20, 459, 1995
Face pumped, water cooled 40 W TEMoo mode
output power 25 - 10W fiber coupled laser
diodes 250 W pump power Cost 280k in 1995