1. Chirped Amplitude Modulation Ladar for Range and Doppler Measurements and 3-D Imaging
Barry Stann, Brian Redman, William Lawler, Mark Giza, John Dammann, Army Research Laboratory
Dr. Keith Krapels, Office of Naval Research
SPIE Defense & Security Symposium
April 2007
The work presented here was jointly sponsored by CDR Keith Krapels, Ph.D., Office of Naval Research, and the Army Research Laboratory.

2. ONR Ladar Concepts of Employment
Cruise Missile Tracking
Coarse Range:
Range-Doppler Tracking:
3D Imaging for Force Protection
Coarse Range:
3D Imaging:

3. Chirped AM Ladar System Block Diagram

4. Chirped AM Range-Doppler Measurement Theory
Frequency
Transmitted/LO
fIF
Received
fstop fD Dt
fstart
Tchirp
Time
Intermediate Frequency (IF) Signals for Each Chirp 2D
FFT
I think this would be clearer if you stated it a little differently. Given the tau is the round trip time to the target, ctau/2 is the range, from plot y=mx+b, m=delatF/T
Freceive = ftrans(x-tau), fif = ftrans(x)-ftrans(x-tau) = mx +b – (m(x-tau)+b) = mtau don’t need all the steps but the answer is clearer I think. (geometry works)
Slow Time = Chirp-to-Chirp

5. ONR Ladar Field Test Setup at CBD
256X256X256 Image at 295 m
Range-Velocity Plot
(V=1.566 m/s, Range=2.166 km)

6. ONR Advanced Breadboard Ladar (2006)
High Power Long Pulse EDFA
Erbium amplifier contract start delayed
Image tube wore-out before October field test at Fort A.P. Hill
New field test planned with new image tube and high power EDFA when available

7. FOPEN Breadboard Ladar
NVESD foliage penetration data collection
Military targets
Ground-to-ground
Multi-aspect
100 m range
FOPEN breadboard ladar
1.55 µm, 1 W diode laser
31 mm receiver aperture
100m range
128x128x128 Image
1 s frame time
.5 m range resolution

8. FOPEN Ladar Illuminator
Quintessence Photonics Diode Laser
1550 nm
1 W
Single transverse mode
Separate Osc./Amp. Sections facilitate modulation
Amp. Section < 4 A
Osc. Section < .7 A
Efficiency > 20 %
Laser
Osc. driver
RF amp.
Illuminator Characteristics
Modulated Output Power ~ .7 W
Bandwidth = 440 MHz
Buck converters for TE cooler and Oscillator drivers
1 W Mini-Circuits Amp drives oscillator
RF Drive = 4-5 mW
TE cooler
driver

9. ONR/FOPEN Breadboard Components
Frequency synthesizer:
400 MHz bandwidth
Oscillator and delayed local oscillator
Programmable thru PC (bandwidth, center frequency, chirp period, delay)
Low cost parts
Can be made smaller (4”X4”) and cheaper
Better synthesizer chip will be available
Receiver:
330 MHz demodulation bandwidth
Uses Intevac InGaAs image tube
250 Vp-p local oscillator voltage added to tube cathode to anode voltage
Eliminated LO voltage interference with CMOS sensor over bandwidth
PC control of cathode to anode voltage
PC control of CMOS sensor parameters
Fan sufficient for rf amplifier cooling
Computer:
Window control of system parameters
Processes 128x128x128 image in 1 s
Displays 3-D image in stereo
Diagnostic windows available
Target tracking possible
Illuminator:
Built around Quintessence Photonics 1.55 µm laser diode (oscillator/amplifier)
Uses Analog Technologies laser and TE cooler drivers (chopper designs)
5 W input yields 330 mW light power
330 MHz modulation bandwidth
Contains Mini-Circuits amplifier for modulating laser
Cost for illuminator is $ 1.5 k

10. FOPEN Breadboard Ladar Initial Results
Top of ladder
~25 m range
S/N~20
little time on tube
Side view
Breadboard Issues/required fixes
Short tube lifetime, heating to install ground plane
Lossy receive lens, poor focus (2X)*
Non-delivery of high current laser driver (3X)*
Illumination field > Receiver FOV (2X)*
ROIC noisy over most of FPA (3X)*
Other system/circuitry clean-up (1.5X)*
(*Potential S/N increase (NX))

11. Imaging with Improved FOPEN Breadboard
19”
24”
Wood Crate at 85 m (front)
Wood Crate at 85 m (side)
Ladar Image (front)
Ladar Image rotated 90 deg.

12. Desired Image Tube Redesign
Chirp
Cathode
MSM Array
CDMA ROIC
Chirp
Cathode
CMOS Sensor
Chirp
MSM Detector
Present tube design
Revised tube design
Narrowband filter required to attenuate solar background
Conversion efficiency is low
RF amp requires high prime power and is expensive
Ladar frame-rate limited to low Hz
RF bandwidth limits range resolution to .5 m
High RF fields can disrupt operation of CMOS sensor
Conversion efficiency is high
Maximum tube gain can be exploited
RF amplifier is low power
Video frame-rates are possible
GHz RF bandwidths achievable (.1 m range resolution)
MSM detector rejects solar background

13. CONCLUSIONS
ONR advanced breadboard will be field tested with high power Erbium amplifier when available
FOPEN ladar enables extensive check-out of various changes and improvements to the ONR receiver
The diode laser (Quintessence Photonics) is a great source for short-range ladar applications using the chirped AM architecture
The FOPEN ladar demonstrates that large format (128x128x128 pixels) 100 m imaging is possible with Intevac image tube and low power diode source
Redesign of the Intevac image tube is required for a viable ladar system