Extinction measurement with open-path cavity ring-down technique of variable cavity length.

Area of Science:

• Atmospheric Optics
• Spectroscopy
• Environmental Science

Background:

• Optical extinction measurement is crucial for atmospheric studies.
• Existing methods often require closed-path cells, limiting real-time monitoring.
• A need exists for in-situ, absolute extinction measurements.

Purpose of the Study:

• To develop and validate a variable cavity length open-path cavity ring down (OPCRD) technique.
• To measure optical extinction (scattering and absorption) of air at 635 nm.
• To enable real-time environmental monitoring without sample cells.

Main Methods:

• Utilized a variable cavity length OPCRD setup.
• Experimentally determined ring-down times at different cavity lengths.
• Calculated total cavity loss dependence on cavity length.

Main Results:

• Established a linear relationship between total cavity loss and cavity length.
• Determined air extinction coefficients ranging from 10.46 to 84.19 Mm⁻¹ (ppm/m) at 635 nm.
• Demonstrated the technique's applicability in a laboratory environment.

Conclusions:

• The variable cavity length OPCRD technique provides accurate absolute extinction measurements.
• This method is suitable for real-time environmental monitoring of air optical properties.
• The technique eliminates the need for closed-path sample cells and background measurements.