High-power semiconductor High-power semiconductor lasers for in-situ sensing of lasers for in-situ sensing of

atmospheric gasesatmospheric gases

Carl BorgentunMicrodevices laboratory (MDL),

JPL/Caltech

Copyright 2013 California Institute of Technology.Government sponsorship acknowledged.

OutlineOutline

• Background

• Laser design and fabrication

• Performance

• Next target

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BackgroundBackground

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Gas sensingGas sensing

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Earthscience

Planetary science

Safety

Credit: NASA

Credit: Richard W. Pogge, Ohio state university

Absorption spectroscopy basicsAbsorption spectroscopy basics

Credit: David Sayres, Harvard

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Laser spectroscopy basicsLaser spectroscopy basics

LaserLaser Detector

DetectorGasGas

1980sLiquid helium-cooled lasers (1000kg)

1990sLiquid nitrogen-cooled lasers (70 kg)

2000sThermoelectrically cooled lasers (0.1 kg)

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Example application – Earth Example application – Earth

sciencescience

Carnegie airborne observatory

Credit: Carnegie institute of science

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Earthscienc

e

Example application – Planetary Example application – Planetary

sciencescience

Mars polar lander

Mars science laboratory

Credit: NASA

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Planetary

science

Example application – SafetyExample application – Safety

Carbon monoxide monitoring instrument

Credit: NASA

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Safety

Ozone depletionOzone depletion• Chlorine compounds destroy ozone, but only at

cold temperatures.• Water vapor in the stratosphere increases the

threshold temperature, at which ozone destruction can take place.

• Risk of thinner ozone layer not only at the poles, but also at lower latitudes where people, animals, and plants live.

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James G. Anderson et al., Science, 337 (6096), 835-839, 2012.

• Various explanations for high mixing ratios of water vapor, distinguishable by measuring water isotopologues.

• Traditional absorption techniques are not sensitive enough for the simultaneous measurement of water and its less abundant isotopologues.

• Jim Anderson’s group at Harvard are developing a cavity-enhanced instrument.

• A high-power laser source at the right wavelength is needed.

• In this case: Right wavelength ~ 3777 cm-1 (2.65 µm)

• In this case: High-power > 10 mW

Need for more sensitive Need for more sensitive

instrumentinstrument

Credit: NASA; Jim Anderson, Harvard

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Laser design and Laser design and fabricationfabrication

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Two criteria:•Optical gain•Cavity

Laser crash courseLaser crash course

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Active mediumActive medium

Cavity

Pumping

Mirror

Output beam

Molecular Beam EpitaxyMolecular Beam Epitaxy

Credit: JPL

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Active regionActive region

215 nm215 nm

66 Å

ProcessingProcessing

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Etch ridge

Insulate and contact

Etch grating

Single-mode emissionSingle-mode emission

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Wavelength [µm]

Wavelength [µm]

GratingGrating• Distributed feedback (DFB) laser

using a Bragg grating => single-mode emission.

• Etched, i.e. non-metal => less loss.

• Laterally coupled => no epitaxial re-growth necessary.

Credit: JPL

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Wavelength [µm]

Wavelength [µm]

SEM picturesSEM pictures

Credit: Cliff Frez

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Coating, cleaving, and bondingCoating, cleaving, and bonding

Credit: Cliff Frez

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Wavelength:

2.0 – 3.5 µm

Wavelength:

2.0 – 3.5 µm

PerformancePerformance

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Power characteristicsPower characteristics• Output power at 35 mW @ 10C, 600 mA.• Still more than 20 mW @ 30C, 600 mA.• No sign of thermal roll-over.• Dips in LI curves are due to absorption of ambient

water (feature, not a bug!).

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Spectral performanceSpectral performanceWavelength is tunable by temperature and/or drive current.

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Reliability and life-timeReliability and life-time• Reliability and life-time test: devices submitted to

elevated drive currents and mount temperatures.• Over 3000 hours of accumulated testing has been

performed, without a single failure.• Peak wavenumber stabilizes after 100-200 hours.

The change in peak wavenumber is less than 2 cm-1. The output power is not reduced.

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• Lasers integrated into TO-3 packages.

• No significant degradation in performance noticed after packaging.

PackagingPackaging

BeforeBefore AfterAfter

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Shape of output beamShape of output beam

• Divergent and highly elliptical, normal for edge-emitters.

• Divergence angles: ~ 110 and 40 degrees.

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Instrument aperture

Instrument aperture

Collimating the beamCollimating the beam

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LaserLaser

LaserLaser

Laser package

Laser package

Package with internal lensPackage with internal lens

TO-3 headerTEC

Tilted, coated, sapphire window

Black housingCoated lens (XYZ active alignment)

Precision spacerLaser

Cu submount

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Next target: CH4Next target: CH4

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Initial resultsInitial results

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• Hit target wavelength (3058 cm-1).

• Increase in output power (6 mW vs 1.5 mW)

SummarySummary

• Successfully delivered 2 laser modules emitting more than 10 mW at 3777 cm-1 to Harvard for water detection.

• Developing laser package complete with collimating optics.

• Initial results show promising outlook for future methane detection missions like TLS.

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AcknowledgementsAcknowledgements

Supervisor:Siamak Forouhar

Colleagues:Cliff Frez, Ryan Briggs, Mahmood Bagheri

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Thanks for the attention!Thanks for the attention!

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High-power semiconductor High-power semiconductor lasers for in-situ sensing of lasers for in-situ sensing of

atmospheric gasesatmospheric gases

Carl Borgentun, Microdevices laboratory (MDL)