AEOLUS STATUS

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)

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