meso-Tetraphenylporphyrin (TPP) and its two substituted derivatives (meso-tetrakis(4-cyanophenyl)porphyrin [TPP(CN)₄] and meso-tetrakis(4-methoxyphenyl)porphyrin [TPP(OMe)₄]) were synthesized. Their nonlinear absorption and refraction properties were studied using the Z-scan technique in the picosecond (ps) and nanosecond (ns) regimes. The open aperture Z-scan results reveal that TPP and TPP(CN)₄ display an identical reverse saturable absorption (RSA) character in the ps and ns regimes. While TPP(OMe)₄ exhibits a transition from saturable absorption (SA) to RSA in the ps regime and a typical RSA character in the ns regime. The closed aperture Z-scan results show that TPP(CN)₄ and TPP(OMe)₄ have regular enhancement of the magnitude of nonlinear refraction as compared to their parent TPP in both the ps and ns regimes. In addition, the second-order molecular hyperpolarizabilities (γ) of these three porphyrins are calculated, and the γ values of TPP(CN)₄ and TPP(OMe)₄ are remarkable larger than that of TPP. The introduction of the electron-withdrawing group CN and the electron-donating group OMe into TPP has enhanced its nonlinear refraction and γ value, and tuned its nonlinear absorption (TPP(OMe)₄), which could be useful for porphyrin-related applications based on the desired NLO properties.

The development of organic nonlinear optical (NLO) chromophores is vital for various fields such as two-photon biomedical imaging, optical limiting, etc. In this work, two bis-chalcone molecules 1,4-bis[3-(2,4-dimethoxyphenyl)-2-acryloyl]benzene (C1) and 4,4′-bis[3-(2,4-bimethoxy phenyl)-2-acryloyl]biphenyl (C2) were synthesized and characterized. The excited-state dynamics of these two chromophores were studied using femtosecond transient absorption (TA) measurements. And their broadband nonlinear absorption properties and optical limiting (OL) response were investigated by femtosecond open-aperture Z-scan and intensity-dependent transmittance measurements in the wavelength range from 515 nm to 800 nm, respectively. The TA results demonstrate that C2 has strong excited-state absorption behavior and longer lifetime. In addition, the nonlinear absorption response of C2 was found to be superior to that of C1 in the visible range after 500 nm, which is attributed to a two-photon-absorption induced excited-state absorption mechanism. These results indicate that the nonlinear optical response and excited-state dynamics in bis-chalcone compounds could be enhanced via intramolecular charge-transfer.

Electron injection from perovskite to planar TiO ₂ accelerates with chloride addition, in mesoporous TiO ₂ carrier recombination is slowed.

We report the spectral dependence of the three-photon absorption coefficient γ and third-order nonlinear refractive index n₂ in pristine, Sn-doped and Fe-doped β-Ga₂O₃ crystals using 190 fs pulses in the range of 540–750 nm, i.e., photon energy between half and one-third of the bandgap E_g. The nonlinear coefficient n₂ is found to be independent of Sn or Fe doping, and the maximum value of n₂ is about 4 × 10⁻¹⁹ m²/W when the photon energy is near E_g/2. However, we observe that Fe doping can significantly enhance the γ value in the range of 540–600 nm (near E_g/2) while doping has negligible impact on γ for wavelength larger than 620 nm. Femtosecond pump-probe measurements show that Fe doping induced a fast (∼50 ps) carrier decay process after photo excitation, which could be attributed to the Fe induced deep trap states. We obtain three-photon figures of merit that allow operational intensities up to 100 GW/cm². Our results indicate that β-Ga₂O₃ has great potential for all-optical switching applications in red and near IR regimes.

Metal halide perovskites are currently among the most promising materials to reshape our renewable energy future through photovoltaics. Nevertheless, they are also among the more complicated materials to understand and to engineer functional photovoltaics devices from. Their current performance efficiencies have not reached the highest predicted value of 30.06%. Many efforts have been dedicated to developing MHP materials, while fewer efforts were directed to understand and engineer the interfaces and interfacial properties in MHPs. Recently, the understanding and engineering of interfacial properties in MHPs have become a hot topic due to the vital role of interfaces, especially carrier dynamics, on device stability and efficiency. This perspective highlights the importance of focusing research on interfaces and interfacial carrier dynamics in metal halide perovskites. After introducing current challenges in MHPs interfaces and interfacial engineering, we provide a perspective on the contribution that different time-resolved laser spectroscopies add to the growing field of perovskite photovoltaics.