We review the current state of multiphoton microscopy. In particular, the requirements and limitations associated with high-speed multiphoton imaging are considered. A description of the different scanning technologies such as line scan, multifoci approaches, multidepth microscopy, and novel detection techniques is given. The main nonlinear optical contrast mechanisms employed in microscopy are reviewed, namely, multiphoton excitation fluorescence, second harmonic generation, and third harmonic generation. Techniques for optimizing these nonlinear mechanisms through a careful measurement of the spatial and temporal characteristics of the focal volume are discussed, and a brief summary of photobleaching effects is provided. Finally, we consider three new applications of multiphoton microscopy: nonlinear imaging in microfluidics as applied to chemical analysis and the use of two-photon absorption and self-phase modulation as contrast mechanisms applied to imaging problems in the medical sciences.

Despite all the advances in nonlinear microscopy, all existing instruments are constrained to obtain images of one focal plane at a time. In this Letter we demonstrate a two-photon absorption fluorescence scanning microscope capable of imaging two focal planes simultaneously. This is accomplished by temporally demultiplexing the signal coming from two focal volumes at different sample depths. The scheme can be extended to three or more focal planes.

We for the first time report the incorporation of cobalt into a mesoporous TiO electrode for application in perovskite solar cells (PSCs). The Co-doped PSC exhibits excellent optoelectronic properties; we explain the improvements by passivation of electronic trap or sub-band-gap states arising due to the oxygen vacancies in pristine TiO, enabling faster electron transport and collection. A simple postannealing treatment is used to prepare the cobalt-doped mesoporous electrode; UV-visible spectroscopy, X-ray photoemission spectroscopy, space charge-limited current, photoluminescence, and electrochemical impedance measurements confirm the incorporation of cobalt, enhanced conductivity, and the passivation effect induced in the TiO. An optimized doping concentration of 0.3 mol % results in the maximum power conversion efficiency of 18.16%, 21.7% higher than that of a similar cell with an undoped TiO electrode. Also, the device shows negligible hysteresis and higher stability, retaining 80.54% of the initial efficiency after 200 h.

We demonstrate a novel multifocal, multiphoton microscope that is capable of simultaneous dynamic imaging of multiple focal planes. We show for the first time that multimodal, multiphoton images excited with orthogonal polarizations can be acquired simultaneously in both the transmission and epi directions.

We report the incorporation of all-inorganic highly stable CsPbX 3 (X = I, Br) based perovskite nanoparticles (NPs) on top of a bulk CH 3 NH 3 PbI 3 perovskite thin film. This design utilizes the photogeneration ability of perovskite NPs and also improves the interfacial charge transport which happens to be a critical factor in deciding the photovoltaic performance of any solar cell device. With variation in the lead halide (PbX 2 , X = I, Br, Cl) content, the synthesized CsPbX 3 NPs shows tunable band-edge position and fluorescence characteristics. The interaction of all inorganic NPs with the bulk perovskite resulted in improved hole injection and electron blocking characteristics leading to enhanced light harvesting efficiency. The CsPbBr 3 and CsPbI 3 perovskite NPs were used for fabricating the bulk-NP structure due to their better absorption and valence band edge characteristics. The inclusion of CsPbI 3 NPs on top of the bulk perovskite showed a significant increment in the power conversion efficiency of 28%, in comparison with a reference sample without NPs, due to significant improvements in current density, open circuit voltage, and fill factor.