Accurate determination of low-dimensional materials’ complex refractive index by cavity resonant method

Low-dimensional (LD), especially two-dimensional(2D) materials have unique optical and photoelectric properties which can be used in fields such as nanolasers, sensors and communications. Complex refractive index including refractive index n and extinction coefficient k of LD materials is vital for the design of optical devices. However, it is difficult to be accurately measured because the thickness and size of LD, especially 2D materials, are too small. In this work, a new cavity-resonant method is proposed to solve this problem by embedding materials into dielectric optical microcavities. The n and k of embedded LD materials can be accurately obtained by measuring the shift and intensity of cavity mode with and without them. This method is valid for any monolayer 2D materials since the cavity structures and materials can be prepared separately. The complex refractive index of small size monolayer WS₂ and MoS₂ were obtained by this method for demonstration. The o and e light refractive index of CdS nanoribbon can also be determined by the cavity resonant method easily. The results show that it can precisely determine the complex refractive index of ultrathin and miniature size LD materials, which is especially useful for the study and development of LD materials based optical devices.