Laser Transmitter for the Tropospheric Wind Lidar Technology Experiment

(TWiLiTE)

Floyd Hovis, Fibertek, Inc. Bruce Gentry, NASA Goddard Space Flight Center

FIBERTEK, INC.

FIBERTEK, INC. Laser Transmitter Specifications

Performance Specifications/Design Performance Summary Table

Parameter Specification Design Performance Margin

Wavelength 355 nm 355 nm NA

Laser Energy (UV) >30 mJ 40 mJ @ 1.3% duty cycle > 33%

Pulse Rep Rate 200 Hz 200 Hz NA

Average Power > 6 W 8 W @ 1.3% duty cycle > 33%

Beam Quality, M^2 < 3 < 2.5 17%

Energy in the Bucket > 86% encircled energy into 3x d. l. beam Meet specification TBD

Frequency Stability < 5MHz RMS for 30 sec

< 50 MHz RMS for 30 min

Meet specification

< 30 MHz RMS for 30 min

TBD

40%

Seeding Efficiency >99.9% >99.9 Meets spec

Pulsewidth > 15 ns ~13-15 ns None

Linewidth <120 MHz @ 355 nm ~120 MHz None

Pointing stability < 10% of beam divergence < 10% of beam divergence TBD

Electrical Power (excl. chiller)

550 W 470 W 14%

Thermal Management Conductive or Liquid Cooled Conductive to Liquid NA

Lifetime 1 billion shots (75% diode derating) @ 1064 nm 1 billion shots @ 1064 nm TBD

FIBERTEK, INC. Environmental Design Performance

Environmental Design Parameters - Laser Optics Module

Parameter Operating range Survival rangeAmbient temperature (°C) 10 to 40* -30 to +50Ambient pressure (mbar) 0 to 1050 0 to 1050

Environmental Design Parameters - Laser Electronics Unit

*Assumes liquid cooled interface plate for low pressure operation

Parameter Operating range Survival range

Ambient temperature (°C) 0 to 50* -30 to +50Ambient pressure (mbar) 35 to 1050 0 to 1050

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

Design performance exceeds all environmental performance specifications

FIBERTEK, INC.BalloonWinds, Raytheon, and Air Force Lasers Provided Basis For Key Design

Features

Final acceptance testing was completed in November 2006

Space-Winds Lidar Laser Transmitter

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

Laser module

Electronics module

FIBERTEK, INC.

Laser Transmitter

Conceptual Optical Layout

532/1064 nmoutput

Fiber port

Ring Resonator

Fiber-coupled 1 m seed laser

Optical isolator

Power amplifierLBO

doublerLBOtripler

355 nmoutput

FIBERTEK, INC.Laser Housing Baseline

Design Full Assembly

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

Coolant connection

Signal connectors

Purge port

Power connectors

Coolant connection

FIBERTEK, INC.

Ring Resonator

Laser Housing Baseline DesignOscillator Compartment

Purge port

355 nm nm output window

1064 & 532 nm output window

Coolant connection

FIBERTEK, INC.

Amplifier

Laser Housing Baseline Design Amplifier Compartment

THG

SHG

1064/532 nm output port,external beam dump to be added

355 nm output port, external beam expander to be added

Purge port

Coolant connection

FIBERTEK, INC.Laser Housing Baseline

Design Oscillator Compartment Size

Side View

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

31 cm

14 cm

FIBERTEK, INC. Ring Oscillator Performance Overview

1 m Resonator Design Parameters

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

Pulsewidth 56 sRepetition rate 200 HzPump Energy 0.202 JHeat Dissipation 250 watts

Slab Size 4.2 x 4.2 x 94 mm3 Doping Level 1.1 % Nd3+ Angle of Incidence 57˚ TIR Bounces 12 per pass

Cavity Length 40 cm (physical)Cavity Magnification 1.5Out-Coupling 40 %

Output Pulse Energy 25 mJ Output Pulsewidth13-15 ns Output Beam Size ~3 mm super gaussian (variable)

FIBERTEK, INC.

Power Amplifier Design

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

Brewster Angle Slab Design Features

Modeling predicts that extracting a power amplifier with 25 mJ/pulse achieves 100 mJ/pulse output at 1.3 % duty cycle

Modeled Power Amplifier Performance

Diode pump pulse width (µs)

0 20 40 60 80

1064 nm ouput power (W)

0

5

10

15

20

25

30

Pump conditions 75 W peak 808 nm ouput/bar 4 mm diamter input beam 5 W input power 200 Hz

FIBERTEK, INC. Third Harmonic GenerationResults Of Fibertek IR&D

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)

Type I LBO doubler

355 nm output

Type II LBO tripler

1064 nminput

/2 @ 1064nm

FIBERTEK, INC. Opto-Mechanical Design and Procurement 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

FIBERTEK, INC.

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

FIBERTEK, INC.

COLD1

WARMUP2

FAULT3

HPWR6

LPWR5

DIAG7

ARMED4

Power-up WARMUPFAULTARMEDLPWRHPWRDIAG

ARMEDLPWRHPWRDIAG

LPWRHPWRDIAG

CNTRL INITIALIZE

CNTRL LASERDISARMCNTRL HTRSON

CNTRL CLRINT

CNTRL LASERARM CNTRL LPWRMODE

CNTRL HPWRMODE

CNTRL DIAGMODE

CNTRL LPWRMODE

CNTRL HPWRMODE

CNTRL STOP

WARMUPARMEDLPWRHPWRDIAG

Any activefault

“1”

“4”

“-” (hyphen)

“D”

“7”

“2”

“8”

“C”

“C”

“A”

“A”

Blue text indicates alternative command characterswhen operating laser system from HyperTerminal serial interface

Software Interface Is Complete

FIBERTEK, INC. 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

FIBERTEK, INC. 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

FIBERTEK, INC.

Acknowledgements

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