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Open path atmospheric spectroscopy using room temperature operated pulsed quantum cascade laser
M Taslakov1, V Simeonov, H van den Bergh
1Air and Soil Pollution Laboratory (LPAS), Swiss Federal Institute of Technology (EPFL), Lausanne CH-1015, Switzerland. marian.taslakov@epfl.ch
Summary
A new laser system enables precise, long-distance monitoring of atmospheric gases like ozone. This advanced open path spectroscopy offers superior accuracy and haze resistance compared to older methods.
Area of Science:
- Atmospheric science and spectroscopy
- Laser-based environmental monitoring
Background:
- Traditional atmospheric monitoring methods face limitations in range and accuracy.
- Open path spectroscopy requires robust techniques to overcome atmospheric turbulence.
- Mid-infrared (mid-IR) spectroscopy offers advantages over UV-Vis methods for certain atmospheric species.
Purpose of the Study:
- To demonstrate the application of a distributed feedback quantum cascade laser for long-path open path spectroscopic monitoring.
- To assess the system's capability for detecting ozone, water vapor, and CO2 over a 5.8 km path.
- To evaluate the performance against existing techniques like UV DOAS.
Main Methods:
- Utilized a distributed feedback quantum cascade laser with fast wavelength scanning via thermal chirp (140-200 ns pulses).
- Employed differential absorption spectroscopy targeting ozone's nu(3) vibrational band (1,031 and 1,049 cm(-1)).
- Achieved wavelength tuning of approximately 0.6 and 1.2 cm(-1).
Main Results:
- Successfully monitored ozone, water vapor, and CO2 over a 5.8 km open path.
- Achieved ozone detection with lowest column densities (LCD) of ~0.3 ppmm, significantly better than UV DOAS (2 ppmm).
- Demonstrated immunity to atmospheric haze, an advantage of mid-IR laser sources.
Conclusions:
- The developed distributed feedback quantum cascade laser system is effective for long-path atmospheric monitoring.
- Fast wavelength scanning mitigates atmospheric turbulence effects, crucial for open path measurements.
- This mid-IR approach offers enhanced sensitivity, haze immunity, and the potential to detect a broader range of atmospheric species compared to UV-Vis DOAS.