Metasurface-based intelligent measurement of total angular momentum spectra for beams

Total angular momentum (TAM) of a beam, consisting of spin angular momentum (SAM) and orbital angular momentum (OAM), has attached much attentions in photonics community [1]. With its orthogonality, the power distribution of each single TAM mode is defined as a TAM spectrum, which determines the transverse topological structure of structured light and is an important evaluation indicator especially for TAM-based scenarios like optical skyrmions tailoring [2], optical communication [3], and high security holographic encryption [4]. Hence, identifying TAM spectrum is of great significance. However, current diagnostic methods are capable only of TAM modes detection, whilst the measurement of TAM spectra remains challenging [5, 6]. Here, we present an experimental demonstration of precisely measuring the TAM spectrum with a metasurface-based compact structure. The favorable experimental results demonstrate that our proposal can measure structured beams carrying up to 34 TAM modes precisely [7].