Incoherent broadband cavity enhanced absorption spectroscopy using supercontinuum and superluminescent diode sources

Area of Science:

• Spectroscopy
• Laser Physics
• Environmental Monitoring

Background:

• Cavity enhanced absorption spectroscopy (CEAS) offers high sensitivity for gas detection.
• Traditional broadband sources have limitations in spectral brightness and effective path length.

Purpose of the Study:

• To investigate incoherent broadband CEAS using a tailored supercontinuum source.
• To demonstrate enhanced spectral brightness and long effective path lengths for weak absorption measurements.
• To compare performance against superluminescent diode sources.

Main Methods:

• Tailoring a supercontinuum laser spectrum to match high-reflectivity mirror bandwidth.
• Utilizing CEAS with an effective absorption path length exceeding 40 km.
• Developing a spectral fitting method based on differential optical absorption spectroscopy (DOAS).

Main Results:

• Achieved spectral brightness > 7 dBm/nm.
• Demonstrated broadband measurement of weak CO2 and CH4 overtone transitions (1590-1700 nm).
• Obtained minimum detectable absorption coefficients of 2.2 × 10⁻⁹ cm⁻¹ (supercontinuum) vs. 6.2 × 10⁻⁹ cm⁻¹ (SLED).

Conclusions:

• The tailored supercontinuum source significantly enhances CEAS performance for weak absorption.
• The developed DOAS-based fitting method accurately handles saturation and spectral resolution effects.
• This technique shows great potential for multi-component gas analysis in real-world applications.