Note: cavity enhanced self-absorption spectroscopy: a new diagnostic tool for light emitting matter

Area of Science:

• Spectroscopy
• Analytical Chemistry
• Plasma Physics

Background:

• Traditional spectroscopic methods often require external light sources.
• Analyzing light-emitting samples like plasmas and flames presents unique challenges for absorption spectroscopy.
• Enhancing the effective path length of light within a sample is crucial for improving sensitivity.

Purpose of the Study:

• Introduce Cavity Enhanced Self-Absorption Spectroscopy (CESAS) as a new diagnostic technique.
• Demonstrate CESAS's capability for analyzing light-emitting samples without an external light source.
• Showcase CESAS as a sensitive tool for real-time and in-situ diagnostics.

Main Methods:

• Placing a light-emitting sample (plasma, flame, combustion source) within an optically stable cavity with high reflectivity mirrors.
• Utilizing the sample as both the light source and absorbing medium.
• Trapping emitted light within the cavity for multiple round trips (10^4-10^5) to artificially augment the path length.

Main Results:

• CESAS successfully captured both emission and absorption features simultaneously from light leaking out of the cavity.
• The technique demonstrated its performance on supersonically expanding pulsed hydrocarbon plasma.
• The method provides enhanced sensitivity due to the increased effective path length.

Conclusions:

• CESAS is a straightforward and sensitive diagnostic tool for light-emitting samples.
• The technique eliminates the need for an external light source, simplifying implementation.
• CESAS is expected to become a broadly applicable analytical tool for real-time, in-situ diagnostics in various fields.