Ultra-intense vortex laser generation from a seed laser illuminated axial line-focused spiral zone plate.

Relativistic vortex laser has drawn increasing attention in the laser-plasma community owing to its potential applications in various domains, e.g., generation of energetic charged particles with orbital angular momentum (OAM), high OAM X/γ-ray emission, high harmonics generation, and strong axial magnetic-field production. However, the generation of such relativistic vortex laser is still a challenge to the current laser technology. Using micro-structure targets named axial line-focused spiral zone plate (ALFSZP), we propose a novel scheme for ultra-intense vortex laser generation. In the scheme, a relativistic Gaussian laser pulse irradiates an ALFSZP, and diffracts as it passes through the ALFSZP. Due to the focusing and radial Hilbert transform capabilities of the ALFSZP, the seed laser is converted efficiently to a vortex one which is then well focused in a tunable focal volume. Three-dimensional particle-in-cell simulations indicate that using a seed laser pulse with intensity of 1.3 × 1020 W/cm2, the vortex laser intensity achieved is as high as 1.3 × 1021 W/cm2 with the averaged angular momentum per photon up to 0.73ℏ, promising diverse applications in various fields aforementioned.

Stable pulse-compressed acousto-optic Q-switched fiber laser.

A novel acousto-optic switch operation by a simple laser-diode pumped acousto-optic, Q-switched, ytterbium-doped, double-clad fiber laser is reported. Stable compressed Q-switched sub-40 ns pulses with a beam quality factor (M(2)=2) are achieved at the repetition rate of 1-50 kHz. Q-switched pulses of ~20 microJ pulse energy and 35 ns pulse width are obtained at the repetition rate of 50 kHz. Finally, a reasonable explanation of the novel Q-switched operation is presented.

Calculations of bond dissociation energies and dipole moments in energetic materials using density-functional methods.

We compare the effectiveness of six exchange/correlation functional combinations (Becke/Lee, Yang and Parr; Becke-3/Lee, Yang and Parr; Becke/Perdew-Wang 91; Becke-3/Perdew-Wang 91; Becke/Perdew 86; Becke-3/Perdew 86) for computing C-N, O-O and N-NO2 dissociation energies and dipole moments of five compounds. The studied compounds are hexabydro-1,3,5-trinitro-1,3,5-triazine (RDX), dimethylnitramine, cyanogen, nitromethane and ozone. The Becke-3/Perdew 86 in conjunction with 6-31G** is found to give the best results, although for the dipole moments of RDX, there is a slightly difference that B3P86/6-31G** is less reliable than B3P86/6-31+G**.

High power coherent beam combination from two fiber lasers.

Phase locking of two fiber lasers is demonstrated experimentally by the use of a self-imaging resonator with a spatial filter. The high-contrast interference strips of the coherent beam profile are observed. The coherent output power of the fiber array exceeds 12W and the efficiency of coherent power combination is 88% with pump power of 60W. The whole system operates quite stably and, for the spatial filter, no thermal effects have been observed, which means that we can increase the coherent output power further by this method.