Broadband, background-free methane absorption in the mid-infrared

Area of Science:

• Spectroscopy
• Physical Chemistry
• Chemical Physics

Background:

• Molecular spectroscopy provides insights into chemical processes.
• Accurate measurements of methane's vibrational transitions are crucial for combustion analysis.
• Existing techniques face challenges in broadband spectral acquisition and background suppression.

Purpose of the Study:

• To extend the time-resolved optically gated absorption (TOGA) technique into the mid-infrared (mid-IR) spectral region.
• To measure rotationally resolved, broadband absorption spectra of methane's asymmetric C-H stretch.
• To validate the single-shot measurement capabilities of TOGA for temperature and species concentration determination.

Main Methods:

• Utilized a time-resolved optically gated absorption (TOGA) technique.
• Employed a broadband, femtosecond (fs) excitation source and picosecond (ps) absorption features.
• Extended TOGA to the mid-IR spectral regime (∼3.3 μm) for broadband access (∼150 cm^-1).

Main Results:

• Successfully measured rotationally resolved, broadband absorption spectra of methane's fundamental C-H stretch.
• Demonstrated effective suppression of broadband background spectra for sensitive detection.
• Validated simultaneous temperature and species-concentration measurements in a heated gas cell.

Conclusions:

• The TOGA technique is robust and applicable to mid-IR vibrational spectroscopy.
• This single-shot approach enables sensitive, broadband spectral measurements.
• The method shows promise for applications in combustion diagnostics, including fuel-rich flames.