Chirped Amplitude Modulation Ladar for Range and Doppler

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.

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

Chirped AM Ladar System Block Diagram

Chirped AM Range-Doppler Measurement Theory Frequency Transmitted/LO f. IF Received fstop f. D Dt fstart Time Tchirp Slow Time = Chirp-to-Chirp Intermediate Frequency (IF) Signals for Each Chirp 2 D FFT

ONR Ladar Field Test Setup at CBD 256 X 256 Image at 295 m Range-Velocity Plot (V=1. 566 m/s, Range=2. 166 km)

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

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 • 100 m range • 128 x 128 Image • 1 s frame time • . 5 m range resolution

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 % • 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 m. W Laser Osc. driver RF amp. TE cooler driver

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”X 4”) and cheaper • Better synthesizer chip will be available Receiver: Computer: • • • Window control of system parameters Processes 128 x 128 image in 1 s Displays 3 -D image in stereo Diagnostic windows available Target tracking possible • 330 MHz demodulation bandwidth • Uses Intevac In. Ga. As 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 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 m. W light power • 330 MHz modulation bandwidth • Contains Mini-Circuits amplifier for modulating laser • Cost for illuminator is $ 1. 5 k

FOPEN Breadboard Ladar Initial Results • ~25 m range • S/N~20 • little time on tube Top of ladder Side view Breadboard Issues/required fixes • Short tube lifetime, heating to install ground plane • Lossy receive lens, poor focus (2 X)* • Non-delivery of high current laser driver (3 X)* • Illumination field > Receiver FOV (2 X)* • ROIC noisy over most of FPA (3 X)* • Other system/circuitry clean-up (1. 5 X)* (*Potential S/N increase (NX))

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.

Desired Image Tube Redesign Cathode MSM Array CDMA ROIC CMOS Sensor MSM Detector Chirp Present 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 Revised tube design • 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

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 (128 x 128 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