Methods of improving spatial resolution for IR spectroscopy in atmospheric-pressure plasma systems

Area of Science:

• Plasma Physics
• Spectroscopy
• Chemical Engineering

Background:

• Atmospheric pressure plasma systems present diagnostic challenges due to high-temperature and molecular gas complexity.
• Infrared spectroscopy is crucial for determining concentrations and temperatures in these systems.
• High spatial resolution is needed for atmospheric pressure systems with steep gradients, but current methods compromise optical throughput.

Purpose of the Study:

• To propose and analyze a modified Fourier Transform Infrared (FTIR) spectrometer design for scannable, high spatial resolution absorbance measurements.
• To compare the signal-to-noise ratio (SNR) of the proposed design against the beam diameter reduction method.

Main Methods:

• Modification of a commercial FTIR spectrometer with simple optical elements to enable scannable, high spatial resolution measurements.
• Analysis of the signal-to-noise ratio (SNR) for the proposed optical design.
• Comparison of the SNR performance with the conventional beam diameter reduction technique.

Main Results:

• The proposed design offers improved SNR compared to beam diameter reduction for low plasma radiation levels, while maintaining high optical throughput.
• The system allows for scannable, high spatial resolution absorbance spectrum measurements of complex molecular gas mixtures.
• Achieving sub-millimeter spatial resolution is contingent on the infrared light source's radiating area.

Conclusions:

• The modified FTIR spectrometer design provides a viable method for high spatial resolution diagnostics in atmospheric pressure plasmas.
• This approach balances spatial resolution and optical throughput, offering advantages over traditional methods.
• Further optimization depends on the characteristics of the infrared light source within the spectrometer.