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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 BorgentunMicrodevices laboratory (MDL),
JPL/Caltech
Copyright 2013 California Institute of Technology.Government sponsorship acknowledged.
OutlineOutline
• Background
• Laser design and fabrication
• Performance
• Next target
2013-04-04Postdoc seminar – Carl Borgentun
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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)