Abstract
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.
Highlights
The main advantage of typical magneto-optic imager/imaging (MOI)[1,2,3,4,5,6,7] over magnetic field imager/imaging (MFI) is the possibility of achieving higher spatial resolution by using visible light sources and smaller sizes of the sensing domains
We describe our first attempt to develop the novel MOI based on recently reported spintronic terahertz (THz) emitters[13,14,15] and well-known electro-optic (EO) THz detectors[16] for THz time-domain spectroscopy (TDS)[17,18]
In the non-magnetic (NM) Pt layer with strong spin–orbit interaction, the spin-up and spin-down electrons deflect in opposite directions and produce the ultrafast transverse charge current by inverse spin-Hall effect[24] (ISHE)
Summary
The main advantage of typical magneto-optic imager/imaging (MOI)[1,2,3,4,5,6,7] over magnetic field imager/imaging (MFI) is the possibility of achieving higher spatial resolution by using visible light sources and smaller sizes of the sensing domains. The MOI chip was aligned in a calibrated rotation holder to have the pump beam polarization orthogonal to the < 110 > axis of ZnTe crystal in order to supress the parasitic THz emission generated inside the EO crystal by optical rectification (OR) due to moderate ~0.2 mJ/cm[2] pump/probe fluences with our cross-focusing setup. For this on-chip THz generation/detection scheme, the main THz peak is insensitive to the magnet position and originates from the parasitic OR of the pump beam in the ZnTe crystal.
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