We propose to design, fabricate, and experimentally demonstrate a millimeter-scale, continuous-wave THz emitter based on a whispering-gallery resonator that is pumped by a standard telecom-compatible infrared light. Unlike existing THz sources based on nonlinear optical effects, where enhancement of nonlinear optical phenomena is by compressing light into ultra-short pulses our enhancement mechanism is based on multiple recirculation of an IR light in a high quality-factor whispering-gallery resonator enabling efficient THz generation. Intellectual merit: The proposed work presents an entirely new perspective on the potential use of whispering-gallery resonators to radically improve the performance of existing THz sources. Theoretical investigations provide a deep understanding of fundamental conversion efficiency limitations of whispering-gallery enhanced THz emitters based on parametric oscillation and difference frequency generation. Additionally, the experimental efforts provide an intuitive insight to practical constraints and solutions to develop proper THz couplers and waveguides. Broader Impact: The success of the proposed research will enable high-performance medical imaging, biological sensing, security screening and chemical identification systems. Integration of education with research activities: Undergraduate students and summer interns will be recruited for the research activities, special priority will be given to women and the members of underrepresented groups. New graduate courses will be developed and new teaching modules will be included in undergraduate courses, an update on our research results and educational tutorials will be disseminated to the public via easy-to-navigate web pages, bi-annual seminars and open house visits and scientific demos will be arranged for high school students.
