Methods to correct planar laser-induced fluorescence distributions for local nonuniform laser attenuation

Area of Science:

• Optical diagnostics
• Laser-based flow analysis
• Combustion science

Background:

• Planar laser-induced fluorescence (PLIF) is crucial for mapping molecular density in flows.
• Laser intensity attenuation in opaque environments (sooty flames, dusty flows) complicates PLIF measurements.
• Accurate quantification requires correction for local laser intensity variations.

Purpose of the Study:

• To develop and compare methods for determining local laser intensity in opaque flows.
• To enable accurate PLIF measurements in challenging environments.
• To assess the feasibility of different elastic scattering techniques for extinction correction.

Main Methods:

• Two methods based on elastic light scattering were developed to determine the local extinction factor.
• Method 1: Simultaneous recording of two elastic scattering images from opposite illumination directions.
• Method 2: A simplified approach using a single elastic scattering image.

Main Results:

• Both methods successfully determined local laser intensity by measuring the extinction factor.
• The two-directional scattering method is more accurate but experimentally demanding.
• The single-scattering method offers a practical approximation for extinction correction.

Conclusions:

• Accurate PLIF in opaque flows necessitates local laser intensity correction.
• Elastic light scattering provides a viable approach for extinction measurement.
• The choice between methods depends on experimental constraints and required accuracy.