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Recent technological advances in the field of communications have made near-IR tundable diode lasers (TDLs) of high quality, yet relatively inexpensive. A TDL Absorption Spectrometer (TDLAS) system is currently being developed utilizing two-tone frequency modulation to measure trace atmospheric species using a long, open-path. Although the vibrational transitions in the near-IR are weak (overtones and combinations) compared to the mid-IR (fundamentals), working in the near-IR offers several advantages:

  • high quality lasers and detectors
  • relatively cheap
  • ability to couple laser to a fiberoptic cable - allows portability
  • lasers can be operated at room temperature - no need for cryogenic cold heads
  • few interfering absorbing species - can sample at atmospheric pressure - no pumps

The above advantages to working in the near-IR yield compact, portable instruments well-suited for transportation to remote sites.

The Harris Group is currently working in collaboration with Unisearch Associates Inc. to develop a near-IR instrument capable of simultaneous multispecies measurement. Traditional near-IR measurements have required a separate laser (or instrument) for each desired species. We have obtained a SG-DBR widely tunable laser which is capable of accessing absorption lines of several trace gas species, namely, CO, CO2, ammonia, acetylene, and hydrogen sulfide. Measurements of ammonia are most interesting since it's "sticky" properties don't allow simple sampling. By measuring ammonia in an open path, sampling difficulties are removed.

Last Updated on Tuesday, 09 August 2011 18:35

Updated on December 7th, 2012.