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Recently, there have been intensive and extensive research works on perovskites because of their excellent electrical and optical properties. This review is focused on their multiphoton absorption (MPA) and applications. All the MPA coefficients or cross‐sections reported in the literature are summarized. Many experimental data show that the MPA strengths of nanoscale perovskites are several orders of magnitude greater than their bulk counterparts. The second‐ and third‐order quantum perturbation theories predict that, while the two‐band transitions play a significant role in 3D crystals of perovskites, the exciton‐light interactions dominate in the case of 2D perovskites. Other influencing factors on the MPA magnitudes are also discussed. Their potential applications are also highlighted in laser‐frequency upconversion and sub‐bandgap photodetection. [ABSTRACT FROM AUTHOR]

A simple and effective approach based on the liquid phase exfoliation (LPE) method has been put forward for synthesizing boron quantum dots (BQDs). By adjusting the interactions between bulk boron and various solvents, the average diameter of produced BQDs is about 7 nm. The nonlinear absorption (NLA) responses of as-prepared BQDs have been systematically studied at 515 nm and 1030 nm. Experimental results prove that BQDs possess broadband saturable absorption (SA) and good third-order nonlinear optical susceptibility, which are comparable to graphene. The fast relaxation time and slow relaxation time of BQDs at 515 nm and 1030 nm are about 0.394–5.34 ps and 4.45–115 ps, respectively. The significant ultrafast nonlinear optical properties can be used in optical devices. Here, we successfully demonstrate all-optical diode application based on BQDs/ReS2 tandem structure. The findings are essential for understanding the nonlinear optical properties in BQDs and open a new pathway for their applications in optical devices. [ABSTRACT FROM AUTHOR]

Multiphoton absorption may find many technological applications, such as enhancing the conversion efficiency of solar cells by the utilization of sub‐band‐energy photons, below‐bandgap photodetection through the simultaneous absorption of several infrared photons for photocurrent generation, or light frequency upconversion for high‐resolution, 3D imaging. To enhance multiphoton absorption in semiconducting materials, one of the strategies is to explore low‐dimensional excitons. Here, a quantum perturbation theory on a giant enhancement in three‐photon absorption (3PA) arising from 2D excitons in multilayered crystals of organic–inorganic hybrid perovskites is presented. The maximal 3PA coefficient is predicted to be in the range of 2–7 cm3 GW−2 at 1100 nm, the largest values reported so far for any 2D and bulk semiconductors at room temperature. Excellent agreement between theory and the experimental findings unambiguously demonstrates a pivotal role in the enhancement of 3PA played by 2D excitons. The theory predicts that the resonant 3PA coefficient should be enhanced further by at least two orders of magnitude with very low temperature. The findings are essential for understanding giant 3PA arising from 2D excitons in layered hybrid perovskites and may open new pathways for highly efficient conversion from infrared light energy to either electrical energy or higher‐frequency light emission/lasing. Here, a giant enhancement in three‐photon absorption (3PA) arising from two‐dimensional (2D) excitons is theoretically predicted and experimentally observed in multi‐layered crystals of organic–inorganic hybrid perovskites. This finding is essential for understanding 3PA in layered hybrid perovskites and may open new pathways for highly‐efficient conversion from infrared light energy to either electrical energy or higher‐frequency light emission/lasing. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) Ti3C2Tx (T = F, O, or OH) MXene, a graphene‐like material, is successfully fabricated for an investigation in nonlinear optics. Its nonlinear refractive index (n2 ≈ 10−4 [cm2 W−1]) and third‐order nonlinear susceptibility (χ monolayer (3)≈ 10−7 [e.s.u.]) are experimentally confirmed by spatial self‐phase modulation (SSPM) techniques. Applying its strong Kerr effect, a novel all‐optical switcher based on 2D MXene is designed to realize the modulation of pump light to probe light. This indicates that MXene could act as an information converter in an optical light‐control‐light system. Meanwhile, probe light is induced by the pump light to excite diffraction rings, and the ring numbers of the probe light can be controlled to increase by the regulation of the other pump light. Through modulation of the pump light, the "ON" and "OFF" modes in the all‐optical switcher/modulator can be achieved. This work highlights the potential of Ti3C2Tx MXene materials applied in all‐optical switcher/modulators, which can be considered an important step toward MXene‐based advanced photonics devices. The nonlinear optical response of 2D Ti3C2Tx (T = F, O, or OH) MXene is investigated with spatial self‐phase modulation techniques for application in advanced photonics devices. Through modulation of the pump light, the "ON" and "OFF" modes in the MXene‐based all‐optical switcher/modulator are achieved. [ABSTRACT FROM AUTHOR]

Abstract Few-layer graphene oxide (GO) dispersions is successfully synthesized using liquid-phase exfoliation. Nonlinear optical response of GO is investigated by the spatial self-phase modulation (SSPM) experiments. The nonlinear refractive index and third-order nonlinear susceptibility of GO are measured as 3 n 2 ≈ 3.57 × 10 − 6 c m 2 / W and χ m o n o l a y e r (3) ≈ 6.05 × 10 − 10 (e.s.u.), respectively. Moreover, making use of cross-phase modulation, we designed an all-optical switching light path by our GO dispersions. This principle of the device is changing the intensity of controlling laser beam to modulate the propagation of the signal light. These interesting properties reveal a potential application of GO as a novel design of optical switching device, optical modulators, detectors, etc. Highlights • An all-optical switch device based on graphene oxide was proposed. • The nonlinear coefficient of GO can be measured by SSPM. • A strong laser beam can modulate weak laser beam based on the SXPM. [ABSTRACT FROM AUTHOR]