Infrared-Laser Induced Fluorescence and Instrumental Design

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Infrared-Laser Induced Fluorescence and
Instrumental Design
Michael W. Morton Geoffrey A. Blake Division of
Geology and Planetary Science California
Institute of Technology Pasadena, CA 91125
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Stable Isotope Studies
Applications include Atmospheric
chemistry Geochemistry Bio-geochemistry
?Planetary Exploration
Specific examples Atmospheric
photochemistry Climate studies Biological
influences
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Instrumentation
Mass Spectrometers Utilize mass differences in
isotopes, Great for laboratory studies, but not
in situ Limitations in planetary
exploration Size, weight Remote
operation Sample preparation Sample
destruction Isotopomers/ N15NO 15NNO NN17O
Isotopologues
in situ Stable Isotope Ratio Spectrometer
? Utilize spectroscopic differences in isotopes
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A Brief Look at Photoacoustic Detection
Figures courtesy of Miklos, A. P, Hess
(2001). Am. Inst. Phys., 72, 1938, 1951.
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Photoacoustic Considerations
Indirect absorption technique signal strength
depends on Beers law and cell geometry Cell
volume and sample size Non-selective detection
of mixed samples HDO - D2O Short path
length Good sensitivity
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Sensitivity of PA Detection
Show high laser power spectrum with small peak
detection
cm-1
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IR-LIF Technique

• Small instrument size
• Remote operation
• Little to no sample preparation
• non-destructive
• Isotopomer resolution
• Small sample size

Figure courtesy of Geoff Blake
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Instrumental Setup
dewar
lock-in amplifier scope PC
detector
filter wheel
chopper
PA cell
wavemeter PC
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HDO
Transitions 1 OD stretch 2726.73 cm-1 2
bend 1402.2 3 OH stretch 3707.47 Pump
v1v3 near 1550 nm (can use
telecommunications diode lasers).
6512
6434
0 2 1
1 0 1
3707
1 0 0
cm-1
2727
0 2 0
0 0 1
0 0 0
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HDO Vapor Spectrum
S/N 90
1 pMole HDO in volume imaged onto detector.
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Signal and Noise Analysis
Why is the signal independent of pressure
in a pure gas?
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Signal and Noise Analysis
Microphonic peak (vibrations)
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Signal and Noise Analysis
Limited by warm window?
Figure from Bernath, P.F. (1995). Oxford
University Press, Inc., 8.
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Future Work
Characterize noise H2O quenching of HDO
emissions FM modulation instead of chopper
wheel New integrated sample cell on the order of
lt cm3 Measure isotopic fractionation of water Low
pressure studies lt 100 mtorr New detector, lasers
1 2 3 4 7 5 6
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Acknowledgements
Professor Geoff Blake Vadym Kapinus Dr. Pin
Chen Dr. Keith Matthews The Blake Group