Lasing action from photonic bound states in continuum

Lasing action from an optically pumped bound state in the continuum cavity is demonstrated, of both fundamental interest and with applications from optical trapping to biological sensing and quantum information. Light confined within the radiation continuum Light can be trapped by confining it between mirrors or in a cavity. However, a curious effect of trapping waves in an open system, a continuum, known for almost a century from quantum-mechanics theory, was recently rediscovered as a general phenomenon and applied to acoustics as well as optics. Until now, 'bound in continuum' light states have been realized in passive systems. But here, Boubacar Kanté and colleagues report the construction of nanophotonic structures in which such bound states in a continuum are used to produce laser action at room temperature. The effect could help researchers to explore novel light–matter interaction effects. In 1929, only three years after the advent of quantum mechanics, von Neumann and Wigner showed that Schrödinger’s equation can have bound states above the continuum threshold 1 . These peculiar states, called bound states in the continuum (BICs), manifest themselves as resonances that do not decay. For several decades afterwards the idea lay dormant, regarded primarily as a mathematical curiosity. In 1977, Herrick and Stillinger revived interest in BICs when they suggested that BICs could be observed in semiconductor superlattices 2 , 3 . BICs arise naturally from Feshbach’s quantum mechanical theory of resonances, as explained by Friedrich and Wintgen, and are thus more physical than initially realized 4 . Recently, it was realized that BICs are intrinsically a wave phenomenon and are thus not restricted to the realm of quantum mechanics. They have since been shown to occur in many different fields of wave physics including acoustics, microwaves and nanophotonics 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 . However, experimental observations of BICs have been limited to passive systems and the realization of BIC lasers has remained elusive. Here we report, at room temperature, lasing action from an optically pumped BIC cavity. Our results show that the lasing wavelength of the fabricated BIC cavities, each made of an array of cylindrical nanoresonators suspended in air, scales with the radii of the nanoresonators according to the theoretical prediction for the BIC mode. Moreover, lasing action from the designed BIC cavity persists even after scaling do