october 16-18, 2012working group on space-based lidar winds 1 aeolus status part 1: design overview
TRANSCRIPT
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October 16-18, 2012 Working Group on Space-based Lidar Winds
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AEOLUS STATUS
Part 1: Design Overview
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Outline of the presentation
• Introduction to ALADIN
• Laser transmitter (TXA) specification
• Overview on the Laser optical design
• Overview on the Laser thermo-mechanical design
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• Wind measured by Doppler shift of backscattered light
• Single line-of-sight of horizontal wind (HLOS)
• Sun-synchronous orbit• Random error: < 2 m/s• Zero wind bias < 0.4 m/s
ALADIN Measurement Geometry
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ALADIN Measurement principle
• Doppler shift of backscattered light vs laser pulse
• Aerosols signal (Mie) predominant at low altitude (< 2kms)
• Molecules (Rayleigh) predominant at higher altitude (> 2 kms)
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ALADIN Optical Functional Diagram
RSP principle
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T/R Optics
RayleighSpectrometer
Detection Front-end
Chopper
Receiver Equipments
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ALADIN Instrument Overview
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Instrument Core
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The ALADIN laser Transmitter (TXA)
Parameter Requirements
Energy/pulse > 120 mJ @ 50 Hz PRF
Wavelength
Polarisation
355 nm
Linear, better than 100:1
Beam diameter
Output divergence
7.5 mm
< 400 rad full angle
Pulse duration < 100 ns FWHM
Pulse linewidth < 50 MHz FWHM
Spectral purity 99% of pulse energy within 90 MHz
Frequency stability < 4 MHz rms over the observation time
Tunability + 7.5 GHz for initial adjustment
+ 5 GHz in calibration mode (25 MHz steps, 250 MHz steps)
Tuning accuracy < 1 MHz over 28 min (noise)
< 1.7 MHz rms over 28 min (slow drift)
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The ALADIN Laser Transmitter (TXA)
• The ALADIN Laser transmitter is a Nd:YAG Q-switched Master Oscillator Power Amplifier (MOPA), frequency tripled & Injection-seeded.
• It operates in Continuous Mode with a PRF of 50 Hz
• The injection-seeding principle is based on the Ramp-Hold-Fire
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The ALADIN TXA Functional Block Diagram
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Injection + Master Oscillator section
5 mJ IR energy1 mm @ 1/e2
Rod
Q-Switch
Polarizer
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Amplification Section
Input Energy 5 mJ3.4 mm @1/e2
1st pass Output Energy ~50 mJ
2nd pass Output Energy 130 mJ
3rd passOutput Energy 350 mJ (IR)
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Harmonic section
350 mJ IR Energy
150 mJUV Energy
200 mJIR + VIS
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Laser Opto-Thermo-Mechanical Design description
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Reference Laser Head (RLH)
• Based on two Non Planar Ring Oscillators (monolithic design ensures high stability)
• The Reference Laser is stabilized to a low drift resonator
• The beat signal between seeder laser and reference laser is processed by a digital PLL (frequency locking loop)
• The seeder beam is injected in a monomode fiber connected to the PLH
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Power Laser Head (PLH) Optomechanical Layout
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Power Laser Head (UOB + LOB)
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Upper Optical Bench (UOB) of the PLH
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Master Oscillator (MO)
• Cavity length is folded by 4 mirrors mounted on an Invar plate•The output coupler, the cavity end mirror (on the rod) and the Invar plate are mounted on the UOB
The piezo-actuator holds the output coupler
Invar plate
Rod & RMax
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Pump unit (1)
• Zig-Zag Nd:YAG slab Laser diode pumped in front of the beam TIR for efficient optical energy extraction
• Slab TIR coating LIDT limited @ about 100 MW/cm2
• 1000 W Laser Diodes Stacked Array used @ derated power ( ~700 W)
• Typical lifetime 5.109 shots
LD1 LD3 LD5 LD7
LD2 LD6LD4 LD8
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Pump Unit (2)
• The pump unit (PU) is made in copper
• Conductively cooled unit ( with thermal filler to minimize air-vacuum transition effect)
• Operated @ 50 Hz
• About 200 W average Heat dissipation PU longitudinal cross section
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PUMP UNIT (3)
Pre-Amp PU installed on the UOB
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Harmonic Generation
• LBO crystals used for SHG (25mm) and THG (35mm)
• Type I Phase Matching for SHG, Type II Phase Matching for THG
• Heater controlled crystal temperature higher than 30oC
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UOB Power Laser Head (PLH)
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LOB Power Laser Head (PLH)
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Pump Laser Diodes operation
The heat current will be adjusted according to the formula:to keep constant the distribution of absorbed pump energy in the Nd:YAG rod and slab (same heat dissipation @ laser diode => same emission wavelength)