Noncontact infrared laser sensing of magnetoresistance

The magnetorefractive effect (MRE) has previously been demonstrated to be an effective method for the remote sensing of magnetoresistance. These studies were made using an infrared (IR) spectrometer, which is ideal for technique development and fundamental material characterization but lacks the simplicity of a fixed-frequency measurement in which the intensity is monitored as a function of applied magnetic field--mimicking a traditional four-point probe electrical measurement. Using a carbon dioxide laser as an IR light source, the design of a fixed-frequency instrument in the reflection geometry is presented and tested. Taking into account both drifts and short-term fluctuations, a light intensity detection signal-to-noise ratio of better than 200:1 is achieved in applied magnetic fields of +/-12 kOe enabling detection of MRE of 0.15%. The fixed-frequency instrument provides a noncontact probe of magnetoresistance with the potential for spatial resolution and angular variation.