Realization of UV Plasmonic Nanolasers With Extremely Small Mode Volume

It is difficult to operate plasmonic nanolasers on silver films in the ultraviolet regime owing to the bending-back effect of surface plasmon dispersion. In this paper, we report on plasmonic lasers comprised of a ZnO nanowire lying on a single-crystalline silver film with a SiO₂ spacer layer. The silver can strongly shrink the mode volume, thereby boosting the Purcell factor. Meanwhile, the SiO₂ spacer thickness is optimized to adjust the surface plasmon dispersion curve so that the lasing wavelength can be located at a large dispersion region, thereby achieving a large group index of 55, an ultra-small effective mode volume of 3.5 × 10^-3 λ³, and low-threshold of 11 MW/cm².