A mid-IR ICL-based sensor for field measurements of ambient CH4
We are developing a mid-IR ICL-based sensor for field measurements of ambient CH4. We describe some of the design considerations for this sensor. Our sensor uses a Type II Quantum Cascade Laser (or Interband Cascade Laser, ICL) operating near 3.3 μm to monitor a well-isolated line in the υ3 fundamental band of CH4. The ICL operates in cw mode at cryogenic temperature. The sensor consists of two major components, an optical breadboard containing the laser, transfer optics, sample cell, and detectors, and an instrumentation module containing power supplies and system control computer. Light from the laser is collimated using a reflective microscope objective and transported to a multipass cell via a simple optics train. The multipass cell provides an optical path of ~7 meters in an 0.25 m base path. The spectrometer uses TE-cooled InAs detectors along with our Balanced Ratiometric Detection. Our measured precision for CH4 is 15 ppbv for a 60 sec integration time. We report on additional sensor characterization and data from recent field trials at two facilities maintained by the University of New Hampshire.
Earth Systems Research Center
Proceedings Volume 6386, Optical Methods in the Life Sciences
SPIE Digital Library
Digital Object Identifier (DOI)
Sonnenfroh, D. M., R. K. Varner, M. L. Silva, M. G. Allen, (2006) A mid-IR ICL-based sensor for field measurements of ambient CH4 (Invited Paper), Proceedings of SPIE Vol. #6386.
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