A single multiwalled carbon nanotube (MWNT)‐glass fiber is used to monitor the initiation and growth of microcracks in composites, which provides an early warning system to detect fracture in materials. An electromechanical microswitch is further constructed based on the connecting/breaking of the nanotube bridges across microcracks under external strain or thermal expansion.

Amplification of spontaneous emission (ASE) at 23.6 nm has been studied in a Ge plasma heated by a 1 TW infrared laser pulse. The exponent of the axial gain reached 21 in a geometry with Fresnel number < 1. Two plasma columns of combined length up to 36 mm were used with an extreme ultraviolet mirror giving double-pass amplification. Saturation of the ASE output was observed. The beam divergence was about 8x diffraction limited with a brightness estimated at 10 14 Wcm~2sr _1 . The feedback from the mirror was significantly reduced probably by radiation damage from the plasma.

No abstract

The application scope of the Poincare-Lighthill-Kuo (PLK) method is suggested by using the Particle-in-cell (PIC) numerical method to study head-on collision of two solitary waves. Comparisons between the numerical results from PIC simulations and the analytical ones from the PLK method indicate that the both are in good agreement with each other. The dependence of the phase shifts after the head-on collision on both amplitudes of two solitary waves is given from our PIC method. It is found that the phase shifts depended on the amplitude of both waves. The maximum amplitude during the colliding process is approximately equal to the sum of both amplitudes for the small amplitude solitary waves.

We propose a scheme to generate single-cycle powerful terahertz (THz) pulses by ultrashort intense laser pulses obliquely incident on an underdense plasma slab of a few THz wavelengths in thickness. THz waves are radiated from a transient net current driven by the laser ponderomotive force in the plasma slab. Analysis and particle-in-cell simulations show that such a THz source is capable of providing power of megawatts to gigawatts, field strength of MV/cm-GV/cm, and broad tunability range, which is potentially useful for nonlinear and high-field THz science and applications.

A compact ultrafast electron diffractometer, consisting of an s-band 1.6 cell photocathode radio-frequency gun, a multi-function changeable sample chamber, and a sensitive relativistic electron detector, was built at Shanghai Jiao Tong University. High-quality single-shot transmission electron diffraction patterns have been recorded by scattering 2.5 MeV electrons off single crystalline gold and polycrystalline aluminum samples. The high quality diffraction pattern indicates an excellent spatial resolution, with the ratio of the diffraction ring radius over the ring rms width beyond 10. The electron pulse width is estimated to be about 300 fs. The high temporal and spatial resolution may open new opportunities in various areas of sciences.

No abstract

Coherent terahertz (THz) emission from the vacuum-plasma interface induced through laser wake-field excitation has been investigated by particle-in-cell simulations. The emission frequency appears around tau(-1)(L), where tau(L) is the laser pulse duration, even though the plasma density is distributed inhomogeneously near the interface. The emission amplitude, which is zero on the propagation axis of the incident pulse, increases transversely until reaching the maximum amplitude at the beam edge of the incident pulse and then decays transversely. The emission power scales like P approximately 10(8) x a(4)(0) W, where a(0) is the normalized field amplitude of the laser pulse. For an incident pulse of a few tens of femtoseconds at the forced intensity of 3 x 10(17) W/cm(2), it can generate THz radiation with a power of a few MW and with an energy of several microJ/pulse.