SRS conversion efficiency assessment of a single cell Raman gas mixture for DIAL ozone lidar

Area of Science:

• Atmospheric physics
• Laser spectroscopy
• Optical remote sensing

Background:

• Differential Absorption Lidar (DIAL) is crucial for atmospheric monitoring.
• Efficient generation of specific wavelengths is essential for DIAL systems.
• Raman scattering offers a method for wavelength conversion.

Purpose of the Study:

• To design and optimize a single Raman cell for DIAL ozone lidar.
• To investigate the conversion efficiency and flexibility of a hydrogen and methane mixture.
• To determine optimal conditions for generating specific wavelengths for lidar applications.

Main Methods:

• Utilized a single Raman cell filled with hydrogen (H2) and methane (CH4) gas mixture.
• Excited the gas mixture with a frequency quadrupled Nd:YAG laser (25 mJ, 10 ns, 100 Hz).
• Examined stimulated Raman scattering (SRS) conversion efficiency at varying pressures and mixing ratios.

Main Results:

• Achieved a maximum total conversion efficiency of approximately 45%.
• The H2:CH4 mixture generated a coaxial beam at 288.4 nm (CH4) and 299.1 nm (H2).
• Optimal conditions were 2:1 H2:CH4 ratio at 18 bar for equal energy output.

Conclusions:

• The single Raman cell configuration is effective for DIAL ozone lidar.
• The H2:CH4 mixture provides a flexible and efficient method for generating required lidar wavelengths.
• Further studies should consider cascade Raman scattering and soot formation effects.