We demonstrate a new method to detect terahertz (THz) power using a temperature-supersensitive capsulized cholesteric liquid crystal film based on the thermochromic and thermodiffusion effect, which is clearly observed. A quantitative visualization of the THz intensity up to 4.0 × 10³ mW/cm² is presented. The diameter of the color change area is linearly dependent on the THz radiation power above 0.07 mW in the steady state. Moreover, the THz power can be detected for 1 sec of radiation with a parabolic relation to the color change area. The THz power meter is robust, cost-effective, portable, and even flexible, and can be used in applications such as THz imaging, biological sensing, and inspection.

The terahertz emissions from cobalt ferromagnetic heterostructures are demonstrated. The performances of heterostructures Fe/Au and Co/Pt have been compared. The amplitude of the terahertz emission sensitively depends on the non-magnetic materials. The terahertz emission is experimentally proved to be related to the spin currents by checking the terahertz emission using reversed magnetization and sample orientation. We further studied the Pt-layerthickness dependence of the amplitude of terahertz emission. A theoretical model is developed based on a comprehensive analysis of the spin transport. The efficiency of the spin injection from the ferromagnetic to nonmagnetic layer is evaluated by taking into account the interfacial spin loss. This work reveals that interfacial spin loss needs to be carefully addressed for the design of efficient terahertz emitter based on the ferromagnetic/nonmagnetic heterostructure.