NO₂ Sensor Based on Faraday Rotation Spectroscopy Using Ring Array Permanent Magnets

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Environmental Science

Background:

• Faraday rotation spectroscopy (FRS) detects paramagnetic molecules using magneto-optical effects.
• Conventional FRS relies on solenoid coils, which are power-intensive and prone to electromagnetic interference.
• There is a need for more robust and efficient FRS systems for environmental monitoring.

Purpose of the Study:

• To develop a novel, low-power Faraday rotation spectroscopy sensor for nitrogen dioxide detection.
• To overcome the limitations of traditional solenoid-based magnetic field generation in FRS.
• To create a sensor suitable for robust, field-deployable environmental monitoring.

Main Methods:

• A novel FRS approach utilizing a neodymium iron boron permanent magnet ring array and a Herriott multipass absorption cell.
• Generation of a longitudinal magnetic field using 14 permanent magnet rings arranged non-equidistantly.
• Targeting the nitrogen dioxide transition at 1613.25 cm⁻¹ with a quantum cascade laser.

Main Results:

• Achieved an average magnetic field strength of 346 gauss over 380 mm.
• Demonstrated a minimum detection limit of 0.4 ppb for nitrogen dioxide with a 70 s integration time.
• Successfully coupled the permanent magnet array with a Herriott multipass absorption cell.

Conclusions:

• The proposed low-power FRS sensor offers a sensitive and selective method for nitrogen dioxide detection.
• This approach minimizes power consumption and electromagnetic interference compared to traditional methods.
• The system shows promise for development into a field-deployable environmental monitoring solution.