Progress On Laser Transmitters For Direct Detection Wind Lidars Floyd Hovis, Fibertek, Inc. Jinxue Wang, Raytheon Space and Airborne Systems Michael Dehring, Michigan Aerospace Corp. Jan 18, 2006

Program Overview Develop a robust, single frequency 355 nm laser for airborne and space-based direct detection wind lidar systems –All solid-state, diode pumped –Robust packaging –Tolerant of moderate vibration levels during operation –Space-qualifiable design Incorporate first generation laser transmitters into ground-based and airborne field systems to demonstrate and evaluate designs –Goddard Lidar Observatory for Winds (GLOW) –Balloon based Doppler wind lidar being developed by Michigan Aerospace and the University of New Hampshire for NOAA Develop scaling to higher powers and pulse energies –Raytheon funded Risk Reduction Laser –Air Force SBIR to develop a 1 J, 100 Hz 1064 nm pump source Iterate designs for improved compatibility with a space-based mission –Lighter and smaller –Radiation hardened electronics Fibertek Laser/LIDAR Expertise - Many NASA and DOD SBIRS - Extensive experience in fieldable single frequency laser transmitter development Raytheon Laser/LIDAR Expertise - Over 30,000 laser/lidar systems for DOD - Leader in engineering & packaging rugged laser/LIDAR systems for air and space - Significant IRAD investment A space-qualifiable laser in the same form and factor as the flight laser!

Related Laser Programs at Fibertek CustomerApplication Required 1  m PerformanceProgram Status Raytheon Doppler Wind Lidar1000 mJ at 50 HzFinal build in progress Air ForceRemote Imaging Lidar800 mJ at 100 HzFinal build in progress Univ. of NHDoppler Wind Lidar150 mJ at 50 HzDelivery complete delivered NASA LangleyOzone DIAL900 mJ/pulse at 50 HzFinal build in progress NASA Langley Phase II SBIRSeed & Metrology Laser50 mW single frequencyFunded (4/05 start) NASA LangleyHigh Spectral Res. Lidar 200 mJ at 200 HzFunded (12/05 start) NASA LangleyMars exploration40 mJ at 20 HzFinal contract in negotiation NavyRangefinder/Designator400 mJ at 25 HzFinal contract in negotiation Single frequency pump head & resonator technology will support a significant number of next generation lidar applications We Have Significant Ongoing Support for Space-Qualifiable and Single Frequency Laser Development

Raytheon Related Laser/LIDAR Experience Examples ABL-TILL: Track ILluminator Laser for the Air Force AirBorne Laser Program Advanced Airborne Targeting Laser (500 mJ Nd:YAG) for ATFLIR for F/A-18 (volume production) Synthetic Aperture LADAR for Tactical Imaging (SALTI) Laser Transmitter Receiver (LTR) Laser Electronics Unit (LEU)

Summary of Technical Approach An all solid-state diode-pumped laser transmitter featuring: Injection seeded ring laserImproves emission brightness (M 2 ) Diode-pumped zigzag slab amplifiersRobust and efficient design for use in space Advanced E-O phase modulator material Allows high frequency cavity modulation for improved stability injection seeding Alignment insensitive / boresightStable and reliable operation over stable 1.0  m cavity and optical benchenvironment Conduction cooledEliminates circulating liquids w/in cavity High efficiency third harmonic generationReduces on orbit power requirements Space-qualifiable electrical designReduces cost and schedule risk for a future space-based mission

2005 Accomplishments Delivery of the BalloonWinds laser transmitter for integration at Michigan Aerospace Assembly of the injection seeded ring oscillator for the Raytheon system Diode pumped head has been assembled, tested, and fully vacuum baked for contamination control Optical bench has been populated and vacuum baked Final assembly and test is in progress Validation of the final amplifier design for the Raytheon system The NASA Ozone single-sided pumped amplifiers have been shown to be capable of 100 Hz operation with good beam quality A pair of NASA Ozone single-sided pumped amplifiers will provide the first stage of amplification Incorporation of 100 W diode bar arrays will increase pulse energy from 300 mJ to over 450 mJ for the pair of NASA Ozone style amplifiers in the Raytheon laser A single power amplifier operated at only ¾ power (in both current and pump pulsewidth) has demonstrated over 700 mJ/pulse output for 280 mJ input with good beam quality. This design will be the basis for the final Raytheon laser amplifier The final optical bench and canister design for the Raytheon system is complete Purchase orders have been placed, delivery is due in February Board level assembly of the electronics is complete and testing is well underway Control electronics boards have been fully tested Diode driver testing is underway Electronics housing and thermal interface plate are on order All key features of the optical design have been validated and assembly of the laser module subassemblies have begun

BalloonWinds Laser Transmitter Integrated and Tested Completion of integrated laser and electronics modules for the BalloonWinds system in 2005 validated many of the key elements of the Raytheon design in a packaged unit Injection seeded single frequency ring oscillator Key mechanical design features High voltage power supply design Diode drive electronics Control electronics printed circuit boards and software User interface Thermal control through conductive cooling

Control and Power Electronics Successful acceptance testing of the BalloonWinds laser transmitted has validated the Raytheon Wind Lidar laser transmitter electrical design Interior view of the Laser Electronics Unit DC-DC converters Diode drivers Analog and digital control boards

Control and Power Electronics The control board stack for the Raytheon Wind Lidar laser transmitter has been assembled and tested

Packaged Single Frequency Laser Ring Laser Design Has Been Validated Optical Schematic Design Features Near stable operation allows trading beam quality against output energy by appropriate choice of mode limiting aperture  30 mJ TEM 00, M 2 =1.2 at 50 Hz  30 mJ TEM 00, M 2 =1.3 at 100 Hz  50 mJ square supergaussian, M 2 = 1.4 at 50 Hz Injection seeding using an RTP phase modulator provides reduced sensitivity to high frequency vibration PZT stabilization of cavity length reduces sensitivities to thermal fluctuations Zerodur optical bench results in high alignment and boresight stability 1. Reverse wave suppressor 2. Cube polarizer 3. Odd bounce slab 4. Steering wedge 5. /2 waveplate 6. Mode limiting aperture 7. RTP phase modulator 8. 45° Dove prism 9. Non-imaging telescope 10. RTP q-switch Seed Final Zerodur Optical Bench (12cm x 32cm)

Raytheon 1 J Risk Reduction Laser Optical Layout Final System Optical Configuration Both the original NASA Ozone amplifiers and the power amplifier have been shown to be capable of 100 Hz operation Power amplifier Expansion telescope Amplifier #2 Amplifier #1 LBO doubler 355 nm output LBO tripler Fiber port Ring Resonator Fiber-coupled 1  m seed laser Optical isolator

Amplifier Design First Stage Design Validation 100 Hz Testing of NASA Ozone 1-Sided Pumped Amplifier NASA Ozone single sided pumped amplifiers were reevaluated as first stage of the Raytheon laser transmitter - Recent modeling showed slab bending in 1-sided pumped amplifiers is not as severe as originally believed - NASA Ozone amplifier is also pump on bounce approach but with only 1 array at each bounce point - Beam profile and M 2 were taken for with a single amplifier operated at 100 Hz and 200 µs pump pulse For 30 mJ TEM 00 we achieved over 100 mJ out of a single NASA Ozone Amplifier with an M 2 of 1.2 Dual NASA Ozone style amplifiers operated with 75 W peak optical power per bar meet the requirements of the first amplifier stage for the Raytheon Wind Lidar transmitter 100 Hz M 2 data for a single NASA Ozone amplifier Near field beam profile

Amplifier Design First Stage Output Power Modeling Modeled vs. Measured Results Validate Modeling Approach Based on a simple Franz-Nodvic amplifier approach Oscillator Configuration 100 µs pump pulse 55 W/bar 100 bars Oscillator Output 50 mJ/pulse 0.41 cm x 0.41 cm square beam M 2 = 1.2 Amplifier Configuration Vary pump pulse width 55 W/bar 112 bars/amp Low Energy Telescopic Resonator Application of model to the Raytheon Wind Lidar transmitter design (40 mJ TEM 00 input, 75 W/bar, 200 µs pump pulses) predicts over 500 mJ/pulse output

Amplifier Design Prototype Second Stage Testing Power Amplifier Extraction Results Final amplifier electrical to optical efficiency for 700 mJ output was over 11%. Full system electrical to optical efficiency was over 7%. In-house NASA Ozone laser output used as input to power amplifier TEM 00 ring configuration with 30 mJ output Dual 1-sided pumped amplifiers with only 55 W peak 808 nm output/bar Measured output of power amplifier vs. input from NASA Ozone system 75 W peak 808 nm pump/bar 150 µs pump pulse

Power Amplifier Recent Test Results Pulse energy of > 700 mJ at 50 Hz in a conductively cooled design Preliminary M 2 measurements found a value of ~2 for final amplifier output Near field spatial is a rectangular super gaussian Beam asymmetry in final system will be reduced by fine tuning the cylindrical compensating lens values Near field beam profile Recent prototype testing has validated the power amplifier design

Raytheon Laser Transmitter Predicted Performance Performance for 100% duty cycle, 50 Hz operation Power consumption at 1 J of 1064 nm output 8% electrical to optical conversion 70% primary power conversion940 W 50 W overhead (measured in BalloonWinds) Laser mass-43 kg Laser volume-10 cm x 42 cm x 69 cm = 29,000 cm nm output Hz

Direct Detection Winds LIDAR Laser Transmitter Status in 2006 Demonstration of 1 J/pulse from a single frequency 1064 nm pump laser operating at 50 Hz Demonstration of greater than 45% conversion to 355 nm to achieve 450 mJ/pulse at 50 Hz Completion of a risk reduction engineering model in a space qualifiable, conductively cooled package with the performance given above Improved first stage amplifier efficiency to bring the system electrical to optical efficiency to >8% Amplifier tests to demonstrate scaling to 100 Hz Performance characterization and testing at Raytheon Space and Airborne Systems in Q2 of %, 20%, etc. duty cycle ON and OFF operation demonstration at Raytheon planned for Q2 of 2006 Field demonstration of the risk-reduction laser transmitter at GroundWinds site in Q3 of 2006 Continued Life Testing and characterization in Q and beyond at Raytheon. Demonstrate TRL 5 in 2006

Acknowledgement BalloonWinds laser transmitter is funded by NOAA BalloonWinds Program through UNH and MAC Space Doppler winds LIDAR risk-reduction laser transmitter is funded by Raytheon Internal Research and Development (IRAD)