Transcript ALADIN POWER LASER HEAD (PLH) - Cooperative Institute for

AEOLUS STATUS
Part 1: Design Overview
October 16-18, 2012
Working Group on Space-based
Lidar Winds
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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
October 16-18, 2012
Working Group on Space-based
Lidar Winds
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ALADIN Measurement Geometry
• 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
October 16-18, 2012
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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)
October 16-18, 2012
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ALADIN Optical Functional Diagram
RSP principle
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Detection Front-end
Receiver Equipments
Chopper
T/R Optics
Rayleigh
Spectrometer
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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 mrad 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)
October 16-18, 2012
Working Group on Space-based
Lidar Winds
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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 RampHold-Fire
October 16-18, 2012
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Lidar Winds
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The ALADIN TXA Functional Block Diagram
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Injection + Master Oscillator section
Rod
Polarizer
Q-Switch
5 mJ
IR energy
1 mm @ 1/e2
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2nd pass Output Energy
130 mJ
Input Energy
5 mJ
3.4 mm @1/e2
3rd pass
Output Energy
350 mJ (IR)
1st pass
Output Energy
~50 mJ
Amplification Section
October 16-18, 2012
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Harmonic section
200 mJ
IR + VIS
150 mJ
UV Energy
350 mJ
IR Energy
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Laser Opto-Thermo-Mechanical Design description
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Reference Laser Head (RLH)
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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
October 16-18, 2012
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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)
Rod & RMax
• 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
Invar plate
The piezo-actuator holds the
output coupler
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Pump unit (1)
LD2
LD4
LD3
LD1
LD6
LD5
LD8
LD7
• 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
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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
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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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Lidar Winds
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