Static Magnetic Field Faraday Rotation Spectroscopy

New NO2 Sensor Based on Static Magnetic Field Faraday Rotation Spectroscopy According to research published in Analytical Chemistry, researchers led by Prof. Gao Xiaoming from the Hefei Institutes of Physical Science at the Chinese Academy of Sciences (CAS) have proposed a low-power Faraday rotation spectroscopy (FRS) nitrogen dioxide (NO2) sensor based on ring-array permanent magnets. FRS enables the detection of paramagnetic molecules by detecting changes in the polarization state of linearly polarized light caused by a gaseous medium immersed in an external longitudinal magnetic field. It is not affected by diamagnetic molecules such as CO2 and H2O, thus exhibiting high species selectivity. Additionally, it possesses very high detection sensitivity due to the use of a pair of nearly crossed polarizers, which greatly suppresses noise in laser intensity. Current FRS signals are primarily generated through Zeeman splitting of sample absorption lines modulated by an alternating magnetic field produced by a solenoid coil. However, when activating the magneto-optical effect, this sinusoidal electromagnetic field suffers from high power consumption, generation of large amounts of Joule heat, electromagnetic interference, and other problems. To address these issues, the researchers proposed a static magnetic field FRS detection device based on rare-earth permanent magnets. Based on the magnetic field distribution properties of neodymium-iron-boron (NdFeB) permanent magnet rings, they assembled 14 identical NdFeB permanent magnet rings in an array configuration and obtained a static magnetic field with an average magnetic field intensity of 346 gauss over a length of 380 mm. The interaction between linearly polarized light and the sample was greatly improved by placing the Herriott cell coaxially with the permanent magnet array. A Q-branch spectral feature in the ν3 fundamental band of NO2 at 1,613.25 cm⁻¹ was examined using a mid-infrared quantum cascade laser. An NO2 detection limit of 0.4 ppb was achieved at an optical path length of 23.7 m. Cao Yuan, the first author of the study, said: "We hope to transform this into a robust, field-deployable environmental monitoring system."

Source

More information: Yuan Cao et al, NO2 Sensor Based on Faraday Rotation Spectroscopy Using Ring Array Permanent Magnets, Analytical Chemistry (2023). DOI: 10.1021/acs.analchem.2c04821 / Journal information: Analytical Chemistry / Provided by Chinese Academy of Sciences / https://phys.org/news/2023-01-scientists-no2-sensor-based-static.html