In this paper, we report a quick approach to self-assemble three-dimensional (3D) spongiform nanofiber stacks via electrospinning, which usually fabricates 2D non-woven fiber mats. Through controlling experimental conditions, cone-like polystyrene fiber stacks can be self-assembled on aluminum foil within 30 min. The stacks are able to reach a height of more than 10 cm. Moreover, conversion between the 3D fiber stack and 2D thin film can be controlled. The formation mechanism of the self-assembled fiber stacks and the influence of experimental conditions have also been explored. The 3D fiber stacks may be promising for applications in many fields such as tissue engineering, electrodes of battery, and filtration, etc.

Metal halide perovskites have exhibited excellent properties as absorbers in solar cells, but this may simply be the first of many applications for this intriguing class of materials. Here, we report the nonlinear optical response of t r i i o d i d e ( C H 3 N H 3 P b I 3 ) a n d m i x e d h a l i d e (CH 3 NH 3 PbI 3−x Cl x ) perovskite absorbers. The results show that they have large nonlinear refractive index (NRI), 3 orders of magnitude larger than that of silicon. Particularly, the NRI of CH 3 NH 3 PbI 3−x Cl x is more than two times larger compared to that of CH 3 NH 3 PbI 3 . Meanwhile, both of them have been proven to possess saturable absorption effects with small nonlinear absorption coefficients which indicate that they can maintain excellent absorption under high-intensity irradiation and are favorable to modulators toward large-energy pulsed laser. Taking into consideration the saturable absorption effect, we demonstrated a pulsed laser with the perovskite as a pulse modulator. These results above indicate the potential for perovskites to be employed in nonlinear optoelectronic devices.

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The mid-infrared spectral range extending from 2 to 6 μm is significant for scientific and technological applications. A promising nonlinear oxide crystal La₃Ga_5.5Nb_0.5O₁₄ (LGN) is proposed and fully characterized for the first time to our knowledge. The transparency range extends between 0.28 and 7.4 μm. The two principal refractive indices were measured and we found that the nonlinear coefficient d11 = 3.0 ± 0.1 pm/V at 0.532 μm. The simultaneous fit of data allowed us to refine the Sellmeier equations of LGN and to calculate the tuning curves for optical parametric generation (OPG) pumped at 1.064 μm. Calculations are consistent with recorded data and also show the generation of a supercontinuum between 1.5 and 3.5 μm when pumped at 0.98 μm by a Ti:Sapphire laser.

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