Researchers at the National University of Singapore (NUS) and their partners have introduced an innovative concept termed “supercritical coupling,” which promises a significant enhancement in photon upconversion efficiency. This breakthrough not only challenges conventional thinking but also charts a new course in the realm of light emission control.
Photon upconversion, the process of converting low-energy photons into higher-energy ones, holds immense potential across diverse applications, from super-resolution imaging to advanced photonic devices. However, achieving efficient photon upconversion has been hindered by limitations in lanthanide-doped nanoparticles' irradiance and the critical coupling conditions of optical resonances.
The concept of “supercritical coupling” revolutionizes conventional approaches by harnessing the physics of “bound states in the continuum” (BICs). Led by Professor Liu Xiaogang from NUS's Department of Chemistry and Dr. Gianluigi Zito from the National Research Council of Italy, the research team explores the phenomena of BICs, where light can be trapped in open structures with theoretically infinite lifetimes, surpassing critical coupling limits.
By manipulating interactions between dark and bright modes within these structures, akin to electromagnetically induced transparency, researchers not only amplify local optical fields but also exert precise control over light emission directionality.
Their groundbreaking findings, published in the journal Nature, underscore the experimental validation of supercritical coupling, showcasing an unprecedented eight-orders-of-magnitude increase in upconversion luminescence. The experimental setup involves a photonic-crystal nanoslab embedded with upconversion nanoparticles functioning as microscale light sources and lasers.
The distinctive characteristics of BICs, marked by minimal light dispersion and microscale light spot dimensions, enable precise focusing and directional control of emitted light, heralding new possibilities for light state manipulation.
Prof. Liu emphasizes, “This breakthrough signifies more than just a fundamental discovery; it signifies a paradigm shift in nanophotonics, reshaping our understanding of light manipulation at the nanoscale. The ramifications of supercritical coupling extend beyond photon upconversion, offering potential breakthroughs in quantum photonics and various coupled resonator-based systems.”
“As the scientific community grapples with the implications of this pioneering work, the prospects are vast for a future where light, one of the universe's fundamental elements, can be harnessed with unparalleled precision and efficiency,” Prof. Liu concludes.
Source: National University of Singapore