Design methodology for a Fabry-Perot interferometer used as a concentration sensor

Area of Science:

• Spectroscopy
• Environmental Monitoring
• Optical Engineering

Background:

• Power plant emissions require continuous monitoring for environmental compliance.
• Existing methods for gas concentration measurement can be intrusive or lack specificity.
• Nitric oxide (NO) is a key pollutant with distinct radiative emission signatures.

Purpose of the Study:

• To present the design methodology for a nonintrusive sensor for power plant exhaust.
• To utilize radiative emission from rovibrational transitions for gas concentration measurement.
• To design and prototype a Fabry-Perot interferometer for this application.

Main Methods:

• The sensor design is based on radiative emission spectroscopy.
• A Fabry-Perot interferometer was conceptually designed for moderate spectral resolution and high optical throughput.
• A prototype interferometer was designed using high-temperature nitric oxide emission in a water background.
• The prototype instrument was calibrated and tested using a laboratory simulator.

Main Results:

• The designed sensor requires moderate spectral resolution (≤1 nm) and high optical throughput.
• Predictions indicate a minimum resolvable NO column density of 100 ppm·m at 800 K with a simple background subtraction.
• Improved order sorting is expected to significantly lower the minimum detectable concentration.
• Experimental results from the laboratory simulator are presented and compared with theoretical predictions.

Conclusions:

• The developed design methodology and prototype demonstrate the feasibility of nonintrusive gas monitoring using Fabry-Perot interferometry.
• The sensor shows promise for accurate measurement of nitric oxide in challenging environments like power plant exhausts.
• Further optimization, particularly in order sorting, can enhance the instrument's sensitivity for environmental applications.