Single-shot, planar infrared imaging in flames using polarization spectroscopy.

Area of Science:

• Chemical Physics
• Spectroscopy
• Combustion Science

Background:

• Planar infrared visualization in flames is difficult due to intense thermal radiation.
• Weak fluorescence quantum yields from ro-vibrational transitions limit species detection.
• Existing methods struggle with non-fluorescent, infrared-active molecules in harsh environments.

Purpose of the Study:

• To demonstrate a novel absorption-based coherent optical method for planar flame species imaging.
• To achieve single-shot, high-resolution imaging of molecular species in a combustion environment.
• To overcome the limitations of thermal background radiation and weak fluorescence.

Main Methods:

• Infrared Polarization Spectroscopy (IRPS), an absorption-based coherent optical technique.
• Excitation of hydrogen fluoride (HF) via a rovibrational transition near 2.5 µm (fundamental vibration band).
• Orthogonal pump-probe geometry for high spatial resolution and coherent suppression of thermal emission.

Main Results:

• Achieved single-shot, planar imaging of hydrogen fluoride (HF) in a CH(4)/O(2) Bunsen flame seeded with SF(6).
• Demonstrated effective suppression of thermal background emission using the coherent nature of 2D IRPS.
• Obtained high spatial and temporal resolution in the flame imaging.

Conclusions:

• Infrared Polarization Spectroscopy (IRPS) is a powerful laser-based technique for imaging infrared-active gaseous molecules in flames.
• IRPS overcomes significant challenges posed by thermal radiation and weak fluorescence.
• The method is suitable for visualizing non-fluorescent species in harsh combustion environments.