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Review of Scientific Instruments / Volume 83 / Issue 2 / ARTICLES / Optics; Atoms and Molecules; Spectroscopy; Photon Detectors

Rev. Sci. Instrum. 83, 023101 (2012); http://dx.doi.org/10.1063/1.3680593 (14 pages)

A capillary absorption spectrometer for stable carbon isotope ratio (13C/12C) analysis in very small samples

J. F. Kelly, R. L. Sams, T. A. Blake, M. Newburn, J. Moran, M. L. Alexander, and H. Kreuzer

Pacific Northwest National Laboratory, Richland, Washington 99352, USA

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(Received 2 August 2011; accepted 9 January 2012; published online 6 February 2012)

A capillary absorption spectrometer (CAS) suitable for IR laser isotope analysis of small CO2 samples is presented. The system employs a continuous-wave (cw) quantum cascade laser to study nearly adjacent rovibrational transitions of different isotopologues of CO2 near 2307 cm−1 (4.34 μm). This initial CAS system can achieve relative isotopic precision of about 10 ppm 13C, or ∼1‰ (per mil in delta notation relative to Vienna Pee Dee Belemnite) with 20–100 picomoles of entrained sample within the hollow waveguide for CO2 concentrations ∼400–750 ppm. Isotopic analyses of such gas fills in a 1-mm ID hollow waveguide of 0.8 m overall physical path length can be carried out down to ∼2 Torr. Overall 13C/12C ratios can be calibrated to ∼2‰ accuracy with diluted CO2 standards. A novel, low-cost method to reduce cw-fringing noise resulting from multipath distortions in the hollow waveguide is presented, which allows weak absorbance features to be studied at the few ppm level (peak-to-rms) after 1000 scans are co-added in ∼10 s. The CAS is meant to work directly with converted CO2 samples from a laser ablation-catalytic combustion micro-sampler to provide 13C/12C ratios of small biological isolates currently operating with spatial resolutions ∼50 μm.

© 2012 American Institute of Physics

Article Outline

  1. INTRODUCTION AND MOTIVATIONS
  2. LASER ABSORPTION SPECTROSCOPY ISSUES
  3. EXPERIMENTAL DETAILS
    1. Capillary absorption spectrometer optical layout
    2. Analog lock-in amplifier
  4. RESULTS AND DISCUSSION FOR STATIC FILLED HWGS
  5. CONCLUSIONS

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KEYWORDS, PACS, and IPC

Keywords

infrared spectrometers, quantum cascade lasers

PACS

  • 07.57.Ty

    Infrared spectrometers, auxiliary equipment, and techniques

  • 42.55.Px

    Semiconductor lasers; laser diodes

International Patent Classification (IPC)

  • G01J3/00

    Spectrometry; Spectrophotometry; Monochromators; Measuring colours

  • H01S5/00

    Semiconductor lasers

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.3680593

PUBLICATION DATA

ISSN

0034-6748 (print)  
1089-7623 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

For access to fully linked references, you need to log in.
    B. E. Brumfield, J. T. Stewart, S. L. Widicus Weaver, M. D. Escarra, S. S. Howard, C. F. Gmachl, and B. J. McCall, Rev. Sci. Instrum. 81, 063102 (2010)RSINAK000081000006063102000001.


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