We present direct observation of filamentary plasma grating induced by interference between two noncollinear infrared femtosecond pulses in water by doping with gold nanoparticles. The gold nanoparticles act as scattering media in water and visualize the fine structure of local optical fields of plasma grating. By measuring the variation of local conductivity as laser undergoes filamentation in water, the generated electron density in water is qualitatively studied. Significant enhancement of local electron density is observed at the intersecting region as two laser beams form plasma grating, indicating the breakthrough of clamped intensity of a conventional filament in water.

A low-cost and minimal-processing-step method is demonstrated to synthesize Yb 2 O 3 -ZrO 2 system by laser excitation catalyzed solid-state reaction. With 980 nm CW laser irradiating, near-resonant excitation of Yb 3+ ions can obviously enhance solid state reaction. As the molar content of Yb 2 O 3 rises from 12.5% to 50%, the lattice parameter of Yb 2 O 3 -ZrO 2 ceramic increases distinctly. Among them, high crystal quality of Yb 2 Zr 2 O 7 and Yb 0.2 Zr 0.8 O 1.9 are synthesized at the laser power of 400 W for 10 s. Two obvious Raman peaks of Yb 2 Zr 2 O 7 represent increased Raman activity. X-ray photoelectron spectroscopy (XPS) and Impedance spectroscopy demonstrate the huge amount of the oxygen vacancies in Yb 0.2 Zr 0.8 O 1.9 . Yb 2 Zr 2 O 7 shows lowest thermal conductivity among all the ceramics studied, within the range of 0.497-0.730 W mK −1 from 25°C to 1200°C, which indicates a promising thermal barrier material.

We demonstrate that self‐propagating sintering reaction could be activated and dramatically enhanced by laser excitation of ion dopants in the solid‐state reactants. Near‐resonant laser absorption and subsequent nonradiative decays make the solid‐state reactants be sintered efficiently while ionic excitations catalyze self‐propagating solid‐state reactions. As a prototype demo, we synthesized white light upconversion phosphors NaYbF4:Pr3+/Gd3+. A continuous‐wave laser at 980 nm was used to populate Yb3+ ions in YbF3 to excited level, which react with NaF to preform NaYbF4 nuclei. The preformed nuclei enhanced laser excitation and energy transfer to those ions that could not be directly excited by the pump laser and thus enabled self‐propagating solid‐state sintering synthesis of NaYbF4 microcrystals at quite low laser powers. Laser excitation of Yb3+ ions could also benefit facile rare‐earth ion doping through activated self‐propagating reactions. Gd3+ and Pr3+ ions were doped in NaYbF4 by simply adding Gd3+ and Pr3+ ionic oxides or fluorides in the raw materials. In addition, Gd3+ ions doping in F− anions ambient could transform the NaYbF4 microcrystal phase from cubic to hexagonal and tune upconversion photoluminescence. This synthetic method can be widely applied to synthesize many other solid‐state compounds, perovskite solar cells, photocatalysts, solid oxide fuel cells, and so forth.

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