Research on Nonlinear Optical Properties of Two-dimensional Nanomaterials

Recently, Wang Jun's group, a researcher at the Micro-Nano Optoelectronic Functional Materials Laboratory, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, has made many progress in the study of nonlinear optical properties of two-dimensional nanomaterials.

The research team (Chinese Academy of Sciences International Visiting Scholar Ivan Kislyakov, etc.) systematically studied the stimulated Brillouin scattering behavior and energy characteristics of graphene nanosheets in NMP and aqueous solutions. Studies have found that low-concentration graphene suspensions have a strong stimulated Brillouin scattering quenching effect due to no significant absorption, and there is a linear dependence between the stimulated Brillouin scattering threshold and the graphene absorption coefficient. Through theoretical calculations, the effects of different thermodynamic, electro-optical and acousto-optical parameters on the Brillouin gain factor in the quenching process of stimulated Brillouin scattering are verified. During the formation of carbon bubbles, the concentration and compressibility of the bubbles will change, and will determine the stimulated Brillouin scattering behavior; the effective bubble size is estimated, and the characteristics of the bubbles on the nanosecond time scale can be studied in conjunction with acoustic absorption experiments. These research results can be used to suppress the generation of stimulated Brillouin scattering in some cases, such as laser technology and optical communication networks. Related research results have been published on Optics Express.

The research team systematically studied the stimulated Brillouin scattering and two-photon absorption characteristics of the hexagonal boron nitride (hBN) nanosheet suspension, and measured the two-photon absorption cross-section σ2PA and the Brillouin gain coefficient gB under the action of a 532nm laser. It is found that when the concentration of hBN is low, it shows obvious quenching effect of stimulated Brillouin scattering, which is consistent with the conclusion of graphene suspension; and the two-photon absorption cross section is very large, so BN nanosheets can absorb enough energy to Heat to melting temperature. The quenching of stimulated Brillouin scattering in BN is mainly caused by the melting of BN and the attenuation of sound waves caused by the conversion of nanosheets into nano-droplets when the laser energy is higher than the stimulated Brillouin scattering threshold. The BN dispersion studied in this article has high transparency under low-intensity irradiation, so it can be used as a non-linear optical composite material for all-optical filters and a transparent material dopant with stimulated Brillouin scattering suppression effect . BN suspension is also an interesting model system for studying nonlinear optics and acousto-optic phenomena. Related research results have been published on Optics Express.

In addition, the research team and the research group of Professor Sun Zhenyu of Beijing University of Chemical Technology have jointly developed a large number of high-quality lead iodide (PbI2) two-dimensional nanosheets through liquid glass technology. The resulting dispersion can maintain good stability within 30 days. The study of nonlinear optical properties found that PbI2 nanosheets have saturated absorption (SA) characteristics under 515nm femtosecond pulses and 532nm nanosecond pulses, and the SA response under 6ns pulse excitation is stronger than that under 340fs pulse excitation. The saturation absorption characteristics of PbI2 nanosheets are comparable to some two-dimensional perovskite, graphene, black phosphorus and molybdenum disulfide materials. In addition, the high stability and low unsaturated loss of PbI2 make it have great application prospects in Q-switching, mode-locked lasers, photodetectors and other ultrafast optoelectronic devices. The research results have been published online on ACS Photonics.