Polarization‐Dependent and Wavelength‐Tunable Optical Limiting and Transparency of Multilayer Selenium‐Doped Black Phosphorus

Abstract As one of the hottest 2D materials, black phosphorus (BP) exhibits a narrow band gap, high carrier mobility, exceptional photoelectric and thermoelectric properties. Nevertheless, easy oxidation in air limits its practical application. Here, versatile optical properties of multilayer selenium‐doped BP (Se‐BP) with air stability are reported. Based on polarization‐resolved Raman spectroscopy, which clarifies the sample structure and doping content, the optical absorption information of Se‐BP is investigated by employing polarized linear absorption spectra and femtosecond (fs) laser intensity scanning (I‐scan). Importantly, wavelength‐changed I‐scan results demonstrate a distinct maximum of 5.9% saturable absorption (SA) and 14.2% reverse saturable absorption (RSA) effect whose modulation depths act out polarization dependence. Through the results of I‐scan and fs transient absorption spectroscopy, not only is the origin of RSA proven to be the excited state absorption (ESA), but also the correlation between SA‐induced optical transparency and RSA‐induced optical limiting is discussed and confirmed. This work sheds new light on multifunctional optical applications based on doped BP materials.