Intracavity Faraday modulation spectroscopy (INFAMOS): A tool for radical detection

Area of Science:

• Spectroscopy
• Laser Technology
• Physical Chemistry

Background:

• Faraday rotation is a magneto-optic effect sensitive to magnetic fields.
• Cavity-enhanced spectroscopy increases interaction path length for enhanced sensitivity.
• Nitric oxide (NO) is a critical molecule in atmospheric and biological studies.

Purpose of the Study:

• To introduce and demonstrate the intra-cavity Faraday modulation spectroscopy technique.
• To enhance the interaction path length of laser light with paramagnetic samples.
• To achieve high sensitivity detection of nitric oxide (NO).

Main Methods:

• Coupling optical feedback cavity-enhanced spectroscopy with Faraday modulation spectroscopy.
• Utilizing a continuous-wave quantum cascade laser.
• Employing a linear cavity with high finesse (F=6300) and a water-cooled solenoid.

Main Results:

• Demonstrated a minimum detectable Verdet constant of 4.7×10^-14 rad cm^-1 G^-1 Hz^-1/2.
• Achieved a single-pass rotation angle sensitivity of 1.6×10^-10 rad Hz^-1/2.
• Established a limit of detection for NO of 0.21 ppbv Hz^-1/2.

Conclusions:

• The intra-cavity Faraday modulation spectroscopy technique offers superior sensitivity for NO detection.
• This technique significantly enhances laser-sample interaction for magneto-optic measurements.
• The developed prototype demonstrates a powerful new tool for trace gas analysis.