Program Overview

1. Laser Transmitter Development for Airborne Direct Detection Wind Lidar and High Spectral Resolution Lidar Missions F. E. Hovis, J. Edelman, T. Schum, J. Rudd, and K. Andes Fibertek, Inc., 510 Herndon Parkway, Herndon, VA 20170-5225 Bruce Gentry, NASA Goddard Space Flight Center Anthony Cook, Chris Hostetler, and John HairNASA Langley Research Center

2. Program Overview • Single frequency laser transmitters for NASA Instrument Incubator Programs • TWiLiTE (Tropospheric Wind Lidar Technology Experiment)laser transmitter • 355 nm single frequency • Operate in an unpressurized high altitude aircraft • Direct detection Doppler wind lidar • Source/Pump laser transmitter for High Spectral Resolution Lidar(HSRL)/Ozone DIAL system • Single frequency 1064/532/355 nm laser transmitter • Multi-wavelength HSRL transmitter • 1064 nm and 355 nm pumps for Ozone DIAL • Used to generate used to generate 300/320 nm • Goal is a design that can meet the requirements of both programs

3. Laser Transmitter Specifications Performance Specifications/Design Performance Summary Table A single frequency 1064 nm transmitter capable of dual 20 W outputs meets the needs of both lidar systems

4. Laser Optics Module Environmental TWiLiTE Specifications Environmental Specifications - Laser Optics Module Environmental Design Parameters - Laser Optics Module *Assumes thermal interface plate maintained at nominal operating temperature +/-2°C TWiLiTE environmental specifications drive the mechanical design

5. BalloonWinds, Space Winds, and Air Force Lasers Provided Basis For Key Design Features Environmentally stable single frequency ring oscillator High efficiency power amplifiers Autonomous operation controlled through RS232 serial interface Nominal 28 VDC primary power Space-qualifiable electrical design Conductive cooling to liquid cooled plates bolted to bottom of laser module Three power amplifier version provides 355 nm single frequency output of >450 mJ/pulse @ 50 Hz Design Features Electronics module Laser module Laser Transmitter Modules

6. Space Winds Transmitter Performance Summary Parameter Performance Repetition rate 50 Hz Pulse energy at 1064 nm 888 mJ 3rd harmonic conversion eff. 53.8% Pulse energy at 355 nm 478 mJ 28 VDC power consumption 684 W 1064 nm wall plug efficiency 6.5% (1064 nm laser output to 28 VDC input) 355 nm wall plug efficiency 3.5% (355 nm laser output to 28 VDC input) Beam quality at 1064 nm, M2 2.2 (hor. axis), 2.3 (vert. axis) Beam quality at 355 nm, M2 4.0 (hor. axis), 5.7 (vert. axis) 1064 nm pulse width 14 ns 355 nm pulse width 14 ns LOM mass and size 43 kg, ~10 cm x 42 cm x 69 cm LEU mass and size ~30 kg, ~13 cm x 42 cm x 69 cm

7. TWiLiTE Laser Transmitter Ring Resonator Fiber-coupled 1 mm seed laser Modeling shows that an oscillator output of ~15 mJ can be amplified to the ~75 mJ of 1064 nm needed for TWiLiTE Conceptual Optical Layout Optical isolator LBO doubler LBO tripler Power amplifier 532/1064 nm output Fiber port 355 nm output

8. HSRL/Ozone DIAL Laser Transmitter Ring Resonator Optical isolator Preamplifier LBO doubler LBO tripler Power amplifier #1 355/532/1064 nm output Power amplifier #2 1064 nm output Fiber port Fiber-coupled 1 mm seed laser Modeling shows that a preamplifier is required to achieve the ~25 mJ of 1064 nm needed for efficient extraction of the power amplifiers Conceptual Optical Layout

9. Power Amplifier Optical Design & Modeling Brewster Angle Slab Design Features  6 mm x 6 mm zigzag slab  2-sided diode pumping  2-sided conductively cooled Even bounce Brewster angle design reduces beam pointing change due to slab movement Equal number of 10 bar arrays per string (5) simplifies diode driver electrical design  Modeling assuming 100 W/bar arrays are operated at 75 W/ bar predicts 100 mJ/pulse output for 25 mJ/pulse input for 63 µs pump pulses Mechanical mounts will be scaled down version of Space Winds designs Modeling predicts that extracting a power amplifier with 25 mJ/pulse achieves 100 mJ/pulse output at 1.3 % duty cycle

10. Laser Module Overview • Dual compartment optical cavity • Oscillator and amplifier on opposite sides • I-beam like structure for increased stiffness • No pressure induced distortion of primary mounting plate • Conductively cooling to liquid cooled center plane • Hermetic sealing for low pressure operation Front View Rear View Purge port 1064 & 532 nm output window 355 nm output window Oscillator access port Purge port Coolant connector Coolant connector Signal connectors Power connectors

11. Laser Housing DesignOscillator Compartment Oscillator head Resonance detection photodiode Ring oscillator Modulator & q-switch drive electronics Isolator Periscope Purge port Coolant connection Power connectors

12. Laser Housing DesignTWiLiTE Amplifier Compartment Amplifier SHG THG Purge port Seed laser Coolant connection 1064/532 nm output port, external beam dump to be added 355 nm output port, external beam expander to be added

13. Laser Housing DesignHSRL/Ozone DIAL Amplifier Compartment Preamplifier SHG oven Power amplifiers Periscope THG oven

14. Third Harmonic GenerationModeling Predictions All modeling used SNLO from Sandia Labs Assumes 100 mJ 1064 nm pump energy  Assumes 3.5 mm pump beam diameter  Supergaussian coefficient = 3 25 mm Type II LBO for THG  deff = 0.521 pm/V  Angular sens. = 3.47 mrad-cm  Walkoff = 9.49 mrad  Temp. sens. = 3.43°C-cm Model 355 nm output as a function of the 532 nm fraction of the total pump energy Results show about 55% conversion to 532 nm optimizes the 355 nm output Modeling of Type I SHG in a 25 mm LBO crystal with same 1064 nm input parameters predicts 53% SHG Model predicts that 1064 nm design output of 100 mJ in a 3.5 mm beam can be tripled to exceed the TWiLiTE requirement of 30 mJ Low Energy Telescopic Resonator

15. Laser Electronics Unit (LEU) Overview • Laser Module electronics • Q-Switch Driver • Photo-detector (detects cavity resonance) • SHG/THG Heaters and temperature sensors • Cavity Modulator • Seed Laser & Electronics • Laser Electronics Unit • Power input, filtering, conversion and distribution • Diode Drivers (voltage converter, high-current pulse switching) • Cavity modulator driver (HV power amplifier) • Laser Controller board (pulse timing, system interface, controls) • Temperature Control Boards • Safety Interlocks • All electrical designs were previously developed for the BalloonWinds and Space Winds laser transmitters

16. Laser Electronics Unit Block Diagram • Single shot hardware/firmware based interlocks are a key design feature • Over current • Over pulse width • Over repetition rate • Q-switch only when seeded

17. Multi-State Software Interface Is Well Developed WARMUP FAULT ARMED LPWR HPWR DIAG Power-up Blue text indicates alternative command characters when operating laser system from HyperTerminal serial interface CNTRL INITIALIZE “1” COLD 1 HPWR 6 CNTRL HPWRMODE “C” CNTRL HPWRMODE ARMED LPWR HPWR DIAG CNTRL HTRSON “C” CNTRL LASERDISARM “4” CNTRL LPWRMODE “D” “A” WARMUP 2 ARMED 4 LPWR 5 CNTRL LPWRMODE CNTRL LASERARM “A” “7” CNTRL STOP CNTRL CLRINT “2” CNTRL DIAGMODE “-” (hyphen) LPWR HPWR DIAG “8” FAULT 3 DIAG 7 WARMUP ARMED LPWR HPWR DIAG Any active fault

18. Laser Electronics UnitCavity Control Measured resonance signal Measured resonance signal Phase modulator drive voltage Phase modulator drive voltage • Two component injection seeding • 10 kHz cavity modulation and peak detection • Detected resonances peaks provide timing reference • Phase locked modulator drive and resonance signals • Stabilizes resonance signal waveform and improves frequency stability Locked Resonance Waveform Unlocked Resonance Waveform

19. TWiLiTE Laser TransmitterBuild Status Laser has been characterized optically and is ready for acceptance & environmental testing Laser Electronics Unit Laser Optics Module

20. TWiLiTE Laser Transmitter1064 nm Beam Profile 1064 nm beam profile at THG crystal 15 W 200 Hz

21. TWiLiTE Laser Transmitter355 nm Beam Profiles At THG crystal 50 cm past THG 100 cm past THG 130 cm past THG 2.6 mm diameter 2.3 mm diameter 2.2 mm diameter 2.2 mm diameter Near field propagation profiles of 7.3 W, 200 Hz (36 mJ/pulse) beam

22. TWiLiTE Laser Transmitter200 Hz Beam Quality Data 7.3 W 355 nm 36 mJ/pulse M2x = 1.49 M2y = 1.37 15 W 75 mJ/pulse 1064 nm M2x = 1.23 M2y = 1.15 Beam diameters after focusing lens

23. TWiLiTE Laser Transmitter Summary • Optical performance • 15 W, M2 = 1.2 at 1064 nm, wall plug efficiency of 3.1% • 7.3 W, M2 = 1.5 at 355 nm, wall plug efficiency of 1.5% • 49% THG conversion efficiency • Mass • Laser Optics Module - 16 kg • Laser Electronics Unit - 17 kg • Volume • Laser Optics Module - 31 cm x 25 cm x 14 cm = 10,850 cm3 • Laser Electronics Unit – 38 cm x 30 cm x 19 cm = 21660 cm3 • Power • Measured total 28 VDC power into system is 490 W • Thermal • Estimated total power dissipation is 475 W • Estimated power dissipation in Laser Optics Module is 275 W • Estimated power dissipation in Laser Electronics Unit 200 W • Laser subsystem delivery in February 2008

24. HSRL/Ozone DIAL Laser TransmitterBuild Status Laser is undergoing final harmonic generation optimization Laser Optics Module Laser Electronics Unit

25. HSRL/Ozone DIAL Laser TransmitterOscillator Performance • Meeting < 10 ns pulsewidth was biggest challenge • Reducing rep rate to 150 Hz achieved 13.5 ns • 3.7 W at 150 Hz (24 mJ/pulse) • Low astigmatism • M2 < 1.2 M2x = 1.04 M2y = 1.17 Beam diameters after focusing lens

26. HSRL/Ozone DIAL Laser Transmitter150 Hz Preamplifier Performance 11.5 W 76 mJ/pulse 1064 nm M2x = 1.15 M2y = 1.14 1064 nm beam profile at preamplifier output Beam diameters after focusing lens

27. HSRL/Ozone DIAL Laser Transmitter150 Hz Amplifier #1 Performance 1064 nm beam profile at Amplifier #1 output

28. HSRL/Ozone DIAL Laser Transmitter150 Hz Amplifier #2 Performance 1064 nm beam profile at Amplifier #2 output

29. Acknowledgements Support for the TWiLiTE and HSRL/Ozone DIAL laser transmitter programs was provided by NASA Goddard Space Flight Center and NASA Langley Research Center with funding from the Earth Science Technology Office Instrument Incubator Program