HSRL mass estimate based on CALIPSO

High Efficiency Laser Designs for Airborne and Space-Based Lidar Applications

F. Hovis, R. Burnham, M. Storm, R. Edwards, J. Edelman, K. Andes, P. Burns, B. Walters, Y. Chen, F. Kimpel, E. Sullivan, K. Li, C. Culpepper, J. Rudd, X. Dang, J. Hwang, S. Gupta, T. Wysocki

Fibertek, Inc

LWG August 2010LWG Aug 20101Presentation OverviewApproaches to high efficiency lasers

ICESat-2 class laser design overviewBulk Nd solid-stateHybrid bulk Nd solid-state/Yb fiber

High-efficiency, single-frequency ring laser developmentNASA Phase 1 SBIRLaser Vegetation Imaging System Global Hawk (LVIS-GH) transmitter

Future design updatesLWG Aug 20102Fibertek Design ApproachesDiode-pumped, bulk solid-state 1 m lasersTransverse pumpedWell developed technologyScaling to > 1 J/pulse, > 100 W demonstrated for fieldable systems Maintaining M2 < 1.5 a challenge at higher powersTrue wall plug efficiencies have been limited to ~8%End pumpedWell developed technologyPower scaling has been limited by pump sourcesHigh brightness and power, fiber-coupled pump sources are a rapidly developing and enabling technologyCOTS devices with > 100 W CW from 200 m core fibers are readily availableTrue wall plug efficiencies of 15%-20% are possibleHigh efficiency is easier in low energy, high repetition rate systemsFiber lasersUltimate high efficiency end pumped transmittersKilowatts of high beam quality have been demonstrated in CW lasersHigh brightness and power, fiber-coupled pump sources are a rapidly developing and enabling technologyEnergy scaling is key challengeLWG Aug 20103ICESat-2 Laser RequirementsParameterATLAS Laser TransmitterWavelength532 1 nmPulse Energy1 mJ, adjustable from 300-1000 JPulse Energy Stability10% RMS over 1 sPulsewidth< 1.5 nsRepetition Rate10 0.3 kHzLinewidth/Wavelength Stability85% transmission through 30 pm filterPolarization Extinction Ratio> 100:1Spatial ModeM2 < 1.6, GaussianBeam Diameter15 mm limiting apertureBeam Divergence< 108 radPointing Stability (shot-to-shot)< 21.6 rad (RMS) over 1 sPointing Stability (long-term)< 100 radLifetime5 years plus 60 days on orbitMass20 kgVolume (cm)< 50(L) x 30(W) x 15(H)Wall plug efficiency>5% for 800 J 1000 J energiesOriginal Laser Support Engineering Services (LSES) contract was to support rebuild of original ICESat laser for ICESat-21064 nm50 mJ/pulse50 HzAfter LSES award the ICESat-2 design transitioned to micro-pulse lidar approach updatesLWG Aug 20104Bulk Solid State TransmitterDesign OverviewConsidered multiple design optionsAll bulk solid-stateAll fiberHybridFiber front endFinal bulk solid state ampFinal choice was schedule drivenNeed a TRL 6 laser by February 2011Settled on all bulk solid-state approachShort pulse Nd:YVO4 oscillatorNd:YVO4 preampNd:YVO4 power ampHigh brightness 880 nm fiber coupled pump diodesBetter mode overlapLower thermal loading

Transmitter Optical Schematic532 nm outputLWG Aug 2010Short Pulse OscillatorNd:YVO4 gain mediumNd:YVO4 is more efficient1 ns pulses can be achieved in Nd:YVO4 at fluences well below optical damage thresholdsRelatively high absorption at 880 nmShort linear cavity with electro-optic Q-switch< 1.5 ns pulsewidthLow timing jitterHigh brightness 880 nm fiber coupled pump diodesBetter overlap with TEMoo modeLower thermal effects than 808 nmEOQ-SwitchConduction CooledDiode Array Pump SourceComposite YVO4 rod with HR FiberCouplingOptics/4Output coupler1 m polarizer880 nm HRLWG Aug 2010Typical Short Pulse OscillatorPerformance

Beam profile at output coupler X diameter = 291 m Y diameter = 295 m

ParameterLaser PerformancePulse Energy146 JPulse Energy Stability2.7% RMS over 1 sPulse Width.98 nsRepetition Rate10 kHzPulse Interval Stability< 0.01 sCenter Wavelength (IR)1064.14 nmSpatial ModeM2x - 1.2, M2y - 1.2Pointing Stability (shot-to-shot)0.43% of divergence Pointing Stability (1 hour)0.53% of divergenceLWG Aug 2010Oscillator 1064nm Linewidth Oscillator is linewidth narrowedAnalyzer etalon resolution is 4.9 pm8 mm etalonReflectivity finesse 14Linewidth = 5.9 pm 8

LWG Aug 20108Oscillator/Preamp Results

M2 = 1.3

Total output energy 470 JExtracted energy 357 JPump power @ 10kHz14.5 WOptical to optical efficiency 24.6%LWG Aug 20109Amplifier 1064 nm Performance Most sensitive parameter is pump/seed overlap Mode matching in amplifier is key to high efficiencyLWG August 2010LWG Aug 201010Bulk Solid State Output vs. Total Diode Pump PowerLWG August 2010LWG Aug 2010Bulk Solid-State Optical to Optical Efficiency vs. Total Diode Pump Power

LWG Aug 2010Bulk Solid-State 532nm Beam Quality vs. Amp Pump PowerAmp pump Power (W)532 nm laser powerMx2My2

4012.61.1841.2724012.61.1421.1793210.51.091.1247.61.191.1164.51.031.0482.21.0151.032Beam quality improves at lower amp pump powersLWG Aug 201013532nm Laser Power (W)Mx2My2

12.91.111.097.31.111.145.61.101.13

M2 data at 532 nm with P=12.9WBeam at focus at 532nm with P=12.9W

Bulk Solid-State 532 nm Beam Quality vs. OutputPower Varied by Amp DelayLWG Aug 201014Solid State Brassboard Full Transmitter Performance SummaryLaser meets specifications for Energy: achieved 12.9W at 532nm68% conversion efficiency from 1064nm to 532nm in LBO532nm Laser energy can be tuned with 2 methods:Adjust power amplifier pump powerAdjust timing between Q-sitch pulse and amplifiers. Constant input powerData shows NO change in divergence or pointing.532 nm beam quality: ~ 1.2532 nm pulsewidth: