As intense, ultrashort, kHz-repetition-rate laser systems become commercially available, pulse cumulative effects are critical for laser filament-based applications. In this work, the pulse repetition-rate effect on femtosecond laser filamentation in air was investigated both numerically and experimentally. The pulse repetition-rate effect has negligible influence at the leading edge of the filament. Clear intensity enhancement from a high-repetition pulse is observed at the peak and tailing edge of the laser filament. As the repetition rate of the laser pulses increases from 100 to 1000 Hz, the length of the filament extends and the intensity inside the filament increases. A physical picture based on the pulse repetition-rate dependent ‘low-density hole’ effect on filamentation is proposed to explain the obtained results well.

In this work, we succeeded in synthesis of spinel LiMn2O4 via a facile self-template method. The product displays a micro-/nanohybrid structure. Nanoparticles/plates act as the primary nanoblocks to build the secondary microarchitecture. There is the open space between the nanoblocks and the void space between the secondary structures. Electrochemical tests demonstrate that the as-synthesized sample exhibits superior rate capability and high-rate cycleability when contrasted with its solid counterpart. The initial discharge capacity is 126 mAh/g at 0.1 C, 110 mAh/g at 10 C, and 84 mAh/g at 20 C. The discharge capacity retention of about 80% is obtained after 800 cycles at 10 C. The high capacity and excellent cycling life of the material shows its potential for application as high-power batteries. The improved rate capability and cycleability can be attributed to its secondary structure that can facilitate fast Li-insertion/extraction and buffer the volume expansion/contraction upon cycling.

A TiO2/carbon nanotubes (TiO2/CNTs) composite was synthesized by chemical vapor deposition method with in situ growth of CNTs using hydrothermally treated TiO2 as the starting material. The nanocomposite was characterized by powder x-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, Raman spectrum, and nitrogen adsorption/desorption isotherms and was investigated as an anode material for lithium-ion batteries. The underlying mechanism for the improvement was analyzed by cyclic voltammetry and electrochemical impedance spectroscopy. The in situ synthesized composite showed better electrochemical performance than the pristine TiO2. The in situ formed CNTs not only supply an efficient conductive network but also keep the structural stability of the TiO2 particles, leading to improved electrochemical performance.

The Y-doped (Hf0.6Zr0.4)1-xYxNiSn (x = 0, 0.01, 0.02, 0.04, 0.06, 0.1, and 0.2) half-Heusler alloys have been prepared by levitation melting and spark plasma sintering. The effect of Y doping on thermoelectric properties of the alloys was investigated in the temperature range of 300–900 K. Y-doped samples had the lower electrical conductivity compared with the parent compound without Y doping. The thermal conductivity had weak dependence on Y doping content. The absolute values of Seebeck coefficient decreased significantly when x < 0.04. The sign of Seebeck coefficient turned from negative to positive at room temperature for x = 0.04 and 0.1, which means that the hole carriers became dominant in these alloys. However, the alloys changed to n-type conduction again at high temperatures. The maximum figure of merit value of about 0.45 was obtained at 780 K for the undoped sample.