Large Terahertz Birefringence in Nanocomposite Films Made From Magnetorheological Fluid

In this work, magnetic nanocomposite films were prepared using magnetorheological fluids (MRFs) and were characterized by time-domain terahertz spectroscopy. Applying magnetic field during the curing process of MRFs makes Fe nanoparticles align into a chain-like structure. Permanent anisotropy is solidified in the films, resulting in a birefringence coefficient as high as 0.37 in a frequency range from 0.4 to 2.0 THz. The polarization state of terahertz wave can be converted by rotating the film at room temperature without external magnetic field. When the rotation angle is at 50°-60°, the ellipticity is greater than 0.8 in the frequency range of 1.19-1.6 THz, indicating that the film can be used as a quarter waveplate.