Terahertz Magneto-Optic Sensor/Imager

We are reporting a new type of compact magneto-optic sensor constructed from terahertz-wave spintronic emitter and electro-optic detector. The corresponding terahertz polarization output of the emitter and the detection phase-sensitivity of the detector depend on the vector of the external magnetic field. The emitter/detector pair consists of two small and thin wafers sandwiched together and capped with a thin gold mirror. As a result, the use of bulky terahertz steering/collection optics was completely eliminated in our magneto-optic imager. With such simple on-chip generation/detection scheme for terahertz time-domain setup in reflection-type geometry, we were able to record the raster-scanned image contrast of a permanent magnet in the proximity of the sensor surface. The contrast strongly varies with the magnet orientation and its position with respect to the sensor. The imager spatial resolution depends on chip optical quality for tight femtosecond-laser pump/probe cross-focusing at detector/mirror interface and terahertz generation/detection efficiency. In this respect, the chip robustness to the pump/probe fluences is also an important factor to consider.