Uncertainty analysis of absolute concentration measurement with continuous-wave cavity ringdown spectroscopy
Applied Optics
|March 28, 2008
Summary
Laser frequency jitter is the largest uncertainty in cavity ringdown spectroscopy concentration measurements. Minimizing this and other factors improves measurement accuracy for applications like molecular oxygen analysis.
Area of Science:
- Spectroscopy
- Analytical Chemistry
- Physical Chemistry
Background:
- Cavity Ringdown Spectroscopy (CRS) is a sensitive technique for gas concentration measurement.
- Accurate concentration determination requires understanding and quantifying measurement uncertainties.
Purpose of the Study:
- To analytically derive uncertainty expressions for CRS parameters.
- To experimentally assess systematic errors in a practical CRS system.
- To identify major uncertainty sources in concentration measurements.
Main Methods:
- Analytical derivation of uncertainty expressions for temperature, laser frequency, and ringdown time deviation.
- Experimental assessment using the PQ(35) transition in the A band of molecular oxygen.
- Determination of oxygen line strength.
Main Results:
- Laser frequency jitter identified as the largest uncertainty source, excluding reference line strength.
- Analytical expressions for uncertainty were derived from the CRS model equation.
- The line strength of the PQ(35) transition of oxygen was determined as 8.63(3) x 10(-27) cm(-1).
Conclusions:
- Practical requirements for minimizing uncertainty in CRS concentration measurements were discussed.
- The study provides a framework for improving the accuracy of CRS measurements.
- Achieved relative uncertainty for oxygen line strength was less than 0.4%.
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