Rapid and High Sensitivity Temperature Measurement Based on Near-Extinction Photoelastic Modulated Magneto-Optical Kerr Effect of Fe-Gd Nanofilm

In this study, we demonstrate a novel magneto-optical (MO) thermometer using a MO Kerr effect (MOKE) system optimally configured with a photoelastic modulator (PEM) that combines the optical and pyro effects of Fe-Gd nanofilm to detect transient surface temperatures with high sensitivity and temporal resolution. The ac–dc harmonic ratio of the modulating frequency senses the temperature-induced Kerr signal of the metal film. In previous MOKE systems using a PEM, the optical axis of the analyzer was configured at 45° to maximize the harmonic amplitude. However, the decreased sensitivity of the harmonic ratio in this conventional configuration leads to lower signal-to-noise ratios (SNRs). By configuring the analyzer axis at a near-extinction position close to 0°, the signal gain of the harmonic ratio can be increased, thus significantly improving the SNRs of the temperature measurement. Experimental results based on near-extinction photoelastic modulated MOKE (NEPEM MOKE) of Fe-Gd nanofilm show that the harmonic ratio achieves a resolution better than 0.02 K over a wide range, from room temperature to the Curie temperature of Fe-Gd nanofilm. On this basis, the MO thermometer can capture thermal pulses with a pulsewidth of no less than
$80~\mu \text{s}$
. The proposed method combines the high spatial and temporal resolution of the MOKE, which converts temperature changes into MO signal changes. Therefore, this noninvasive MO thermometer provides a possible method for temperature measurements on the micro- and nanometer scales.