Laser Transmitter for the Tropospheric Wind Lidar Technology Experiment (TWiLiTE
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Laser Transmitter for the Tropospheric Wind Lidar Technology Experiment (TWiLiTE ) Floyd Hovis, Fibertek, Inc. Bruce Gentry, NASA Goddard Space Flight Center. Laser Transmitter Specifications. Performance Specifications/Design Performance Summary Table. Environmental Design Performance.

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Laser Transmitter Specifications

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Laser transmitter specifications

Laser Transmitter for the Tropospheric Wind Lidar Technology Experiment (TWiLiTE)Floyd Hovis, Fibertek, Inc.Bruce Gentry, NASA Goddard Space Flight Center


Laser transmitter specifications

Laser Transmitter Specifications

Performance Specifications/Design Performance Summary Table


Environmental design performance

Environmental Design Performance

Environmental Design Parameters - Laser Optics Module

*Assumes thermal interface plate maintained at nominal operating temperature +/-2°C

Environmental Design Parameters - Laser Electronics Unit

*Assumes liquid cooled interface plate for low pressure operation

Design performance exceeds all environmental performance specifications


Balloonwinds raytheon and air force lasers provided basis for key design features

BalloonWinds, Raytheon, and Air Force Lasers Provided Basis For Key Design Features

Three amplifier design

Autonomous operation controlled through RS232 serial interface

Nominal 28 VDC primary power

Space-qualifiable electrical design

Thermal control through conductive cooling to liquid cooled plates bolted to bottom of laser module

355 nm single frequency output of >380 mJ/pulse @ 60 Hz (23 W)

Deliverable system will undergo extended life testing at Raytheon

Electronics module

Laser module

Space-Winds Lidar Laser Transmitter

Final acceptance testing was completed in November 2006


Laser transmitter

Laser Transmitter

Ring Resonator

Fiber-coupled

1 mm seed laser

Conceptual Optical Layout

Optical isolator

LBO

doubler

LBO

tripler

Power amplifier

532/1064 nm

output

Fiber

port

355 nm

output


Laser housing baseline design full assembly

Laser Housing Baseline DesignFull Assembly

Coolant connection

  • 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

Purge port

Signal connectors

Power connectors

Coolant connection


Laser transmitter specifications

Laser Housing Baseline DesignOscillator Compartment

Ring Resonator

Purge port

355 nm nm output window

Coolant connection

1064 & 532 nm output window


Laser transmitter specifications

Laser Housing Baseline DesignAmplifier Compartment

Amplifier

SHG

THG

Purge port

Coolant connection

1064/532 nm output port,

external beam dump to be added

355 nm output port, external

beam expander to be added


Laser housing baseline design oscillator compartment size

Laser Housing Baseline DesignOscillator Compartment Size

Top View

  • An ~ 31 cm x 25 cm x 14 cm canister accommodates all required optical and electrical components

  • I-beam like mounting structure provides high mechanical stability

  • All optical components are mounted to a surface that to first order does not experience pressure induced deformation

31 cm

25 cm

Side View

14 cm

31 cm


Ring oscillator performance overview

Ring Oscillator Performance Overview

1 mm Resonator Design Parameters

Diode BarsEight 6-bar arrays, 100 W rated-QCW, operated at 75 W peak power per bar

Pulsewidth 56 ms

Repetition rate200 Hz

Pump Energy0.202 J

Heat Dissipation250 watts

Slab Size4.2 x 4.2 x 94 mm3

Doping Level1.1 % Nd3+

Angle of Incidence57˚

TIR Bounces12 per pass

Cavity Length40 cm (physical)

Cavity Magnification1.5

Out-Coupling40 %

Output Pulse Energy25 mJ

OutputPulsewidth13-15 ns

OutputBeam Size~3 mm super gaussian (variable)


Power amplifier design

Power Amplifier Design

Brewster Angle Slab Design Features

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 NASA Ozone designs

Modeling predicts that extracting a power amplifier with

25 mJ/pulse achieves 100 mJ/pulse output at 1.3 % duty cycle


Third harmonic generation results of fibertek ir d

Third Harmonic GenerationResults Of Fibertek IR&D

Type I

LBO doubler

Type II

LBO tripler

1064 nm

input

355 nm

output

/2 @ 1064nm

Characterized Type I LBO doubler for higher damage threshold and linearly polarized residual 1064 nm

- Damage was an issue in early testing with KTP

- LBO damage threshold is ~4X that of KTP

- Low cost (relatively), high quality LBO crystals are now commercially available

 Characterized 25 mm Type II LBO tripler

- High quality, low cost (relatively) has recently become available

- Ion beam sputtered AR coatings have demonstrated high damage thresholds and low

reflectivities for triple AR coatings (1064/532/355 nm)

 Space-qualifiable laser delivered to Raytheon achieved 23 W of 355 nm for 44 W of 1064 nm pump at

50 Hz (52% conversion efficiency)


Laser transmitter specifications

Opto-Mechanical Design andProcurement Status

  • Optical design is complete

  • Long lead optical components are on order

    • 808 nm pump diodes

    • Zigzag slabs for oscillator, preamplifier, and amplifier

  • Mechanical designs of diode pumped laser heads are complete

    • Parts have been ordered

  • Design of laser canister is nearly complete

    • Some detailing of amplifier optical train and external interfaces remains to be done

    • Goal is to order canister in February 2007


Electronics overview

Electronics Overview

  • Laser Module electronics

    • Q-Switch Driver (high-voltage converter, high-voltage switch)

    • 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 Raytheon Wind Lidar laser transmitters


Laser transmitter specifications

Software Interface Is Complete

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


Laser transmitter specifications

Electronics Design and Procurement Status

  • Software design is complete

  • Design upgrades to allow high altitude unsealed operation is well underway

    • Original plan was for commercial power electronics

    • Laser control board design complete

    • Power supply design complete

    • Diode driver design complete

    • Logic power supply design complete

    • Safety controller design in work

    • Updated seeding circuitry in work

    • Crystal oven controller in work

  • Key long lead components are on order

    • High power, high reliability DC/DC converters

    • High reliability EMI filter modules (MIL-STD-461C & D)

    • Hermetic capacitors

  • Electronics are scheduled to be finished in April 2007


Laser subsystem summary

Laser Subsystem Summary

  • Mass

    • Laser Optics Module - 16 kg (based on current design)

    • Laser Electronics Unit - ~22 kg (estimated from BalloonWinds, may decrease

  • Volume

    • Laser Optics Module - 31 cm x 25 cm x 14 cm = 10,850 cm3 (based on current design)

    • Laser Electronics Unit - TBD, expected to be somewhat larger than laser

  • Power

    • Estimated total 28 VDC power into system is 470 W

  • Thermal

    • Estimated total power dissipation is 450 W

    • Estimated power dissipation Laser Optics Module is 250 W

    • Estimated power dissipation Laser Electronics Unit 200 W

  • Laser subsystem delivery in July 2007


Acknowledgements

Acknowledgements

Funding for this program was provided by the NASA Earth Science Technology Office as part of the Instrument Incubator Program


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