Takayuki Kurihara, Hongsong Qiu, Kosaku Kato, Hiroshi Watanabe, Makoto Nakajima
Due to its efficient coupling with electron spins, the application of terahertz magnetic nearfield in metallic microstructures has been attracting attention. While paramagnetic materials that exhibit magneto-optical effect have been known to enable visualization of the terahertz magnetic fields (magneto-optical sampling), the low field-detection sensitivity has been setting a practical limit to the broader application of such a method. Here we propose and experimentally demonstrate that the terahertz magnetic nearfield-detection sensitivity of magneto-optical sampling with terbium-gallium-garnet crystal can be drastically enhanced by cooling the crystal down to cryogenic temperatures in accordance with Curie's law. Our result paves the way for the efficient characterization of the terahertz magnetic nearfield in planer metamaterials.