Mature optical technologies from the microwave frequencies to the X-ray frequencies have dramatically changed our life in the modern society, but there is a notable gap between the mid- and far-infrared light, roughly the frequencies of 5 – 15 terahertz, where there are no good commercial solutions to control light. In our new work published on Advanced Materials, we use quantum paraelectric perovskite SrTiO3, whose atoms couple with terahertz light so strongly that form a new particle called “phonon-polaritons” to realize sub-wavelength THz field focus. Unlike other materials that also support phonon-polaritons in other frequencies and usually in a very narrow range, SrTiO3 works for the entire “new terahertz gap” due to its quantum paraelectricity property. We prove the concept of SrTiO3 phonon-polariton devices in the frequency range of 7 – 13 terahertz by designing and fabricating ultrafast THz field concentrators to achieve a strong transient electric field around gigavolts per meter. Such a strong field may be used to change the materials’ structure to create new electronic properties, or create new nonlinear optical response from trace amounts of specific molecules to be detected by a common optical microscope. Our methodology framework is also applicable for a broad range of phonon-polaritonic materials to work for photonic devices in 3 – 19 terahertz, opening a new route to control light in one of the last under-explored territories. More details in Rice news.
