We propose to design, fabricate, and experimentally demonstrate a new type of THz emitter by exploiting, for the first time, whispering-gallery enhancement in a THz parametric oscillator. The extremely high resonance quality factors offered by these micron-scale whispering-gallery mode resonators offer unprecedented cavity enhancement factors not only for the optical pump, but also for the generated THz wave. Our preliminary calculations show that such enhancement can transform THz sources to allow a coherent (10 GHz bandwidth), linearly polarized, frequency tunable THz emission with 100 times higher power efficiencies compared to the state-of-the art. Intellectual merit: The proposed work presents an entirely new perspective on the potential use of whispering-galley mode resonators to radically improve the performance of existing terahertz sources. Whispering-gallery enhancement allowed us in the past to be the first to experimentally demonstrate (1) Third-harmonic in a micro-resonator, (2) Brillouin scattering in a micro-resonator, and (3) mechanical vibration by radiation pressure. Using this experience we will explore the use of similar whispering-gallery enhancement to benefit optical-to-THz conversion efficiency in a silica micro-resonator. Theoretical investigations provide a deep understanding of fundamental conversion efficiency limitations of whispering-gallery enhanced THz parametric oscillators. They also offer a valuable insight to physical requirements for THz whispering gallery enhancement. Additionally, the experimental efforts provide an intuitive insight to practical constraints and solutions to develop proper silica micro-resonator THz emitters. Broader Impact: The outcome of the proposed research will enable high-performance medical imaging, biological sensing, security screening and chemical identification systems which are currently limited by the low output power of the existing terahertz sources. Integration of education with research activities: A special training program will be constructed to assimilate graduate students working on this type of interdisciplinary research, undergraduate students and summer interns will be recruited for the research activities, special priority will be given to recruitment of talented women undergraduate and graduate candidates and the members of underrepresented groups. Our PhD students is already teaching pupils from underrepresented population; we intend to integrate The THz research into this school activity via a series of experiment in order to attract this students to apply to university at the end of this 3 year project when the children will be 18. New graduate courses and interdisciplinary seminars 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
Existing coherent ultraviolet light sources are power hungry, bulky and expensive. We have found a better way to build compact ultraviolet sources with low power consumption that could improve information storage, microscopy and chemical analysis. In order to realize a compact ultraviolet source with low power consumption, we have optimized a type of optical resonator that takes an infrared signal from relatively cheap telecommunication-compatible laser and, using a low-power, nonlinear process, boost it to a higher-energy ultraviolet beam. The optical resonator is a millimeter-scale disk with a precisely engineered shape and smooth surface polishing to encourage the input beam to gain power as it circulates inside the resonator. We optimized the structure to achieve high gain over a broad range of optical wavelengths. This allows us to make low-cost, wavelength-tunable ultraviolet sources using low-infrared power levels. Finally, we have used the resonator to generate the fourth harmonic of the infrared beam we started with. Like the harmonic distortions you get from new sound frequencies when you crank up a loudspeaker, engineers can generate harmonics of light by using the right materials. By pushing light beams through a nonlinear medium, they can coax out offshoot beams that are double, or in this case, quadruple the frequency and energy of the input beam, and one-quarter of the original wavelength. We have experimentally demonstrated wavelength-tunable ultraviolet light generation from a telecommunication-compatible laser light in a lithium niobate optical resonator at a record-low laser power of 200 mW.
