Enhancement of peak electric fields for spintronic terahertz emitters through bidirectional radiation superposition

Spintronic terahertz emitters (STEs) are highly desirable for terahertz (THz) spectroscopy applications because of their advantages of broadband and high peak fields. However, the emission strength of STE is comparatively low due to the nanoscale thickness of the heterostructure. In this work, we propose a design for STE integrated with an optical cavity structure. The optical cavity superposes the backward-propagating terahertz pulse with its forward-propagating counterpart, resulting in a high peak field THz pulse through constructive interference. Both theoretical analysis and experimental results demonstrate that an increase in the peak field to about 130% can be achieved. Furthermore, we show that the proposed cavity-integrated STE is applicable for observing time-dependent Kerr signals in a diamond crystal. Our findings pave the way for optimizing STE devices and highlight the potential of strong THz field sources in the study of nonlinear effect spectroscopy.