We report measurements of damage threshold and ablation depth for SiO2 and CaF2 irradiated under lasers at wavelengths of 800 and 400 nm for duration of 45-800 fs. These results can be well understood by using a developed avalanche model. The model includes the production of conduction band electrons (CBEs), laser energy deposition, and CBE diffusion. The evolution of microexplosion is investigated based on this model.

We investigate exciton ground states in Si and 3C-SiC quantum dots by using the effective mass theory, taking account of the conduction- and valence-band mass anisotropy as well as the small spin-orbit splitting energy. The degenerate hole and exciton states are partly split by the mass anisotropy. The anisotropy splitting energies in quantum dots are different dramatically from their bulk value due to quantum size effects. The assumed changeable spin-orbit splitting energy may change the ordering of the anisotropy-split energy levels. Taking account of the exchange interaction, the degeneracy of the exciton states is further lifted. Due to the anisotropy and exchange splitting, the 48-fold exciton ground state will be split into two 18-fold triplets and two 6-fold singlets. The lowest three states are optically forbidden for Si quantum dots, which leads to a Stokes shift of luminescence. The theroretical shift agrees well with the experimental data. Furthermore, the exciton band gap and binding energy as a function of dot radius are presented both for Si and for 3C-SiC quantum dots. The band gap of Si quantum dots agrees well with the recent photoluminescence results of size-separated quantum dots by Ledoux et al. and absorption data of Furukawa et al.

Needle-shaped 3C-SiC nanowires were grown from commercially available SiC powders in a thermal evaporation process with iron as catalyst. A strong broad photoluminescence peak located around 450 nm was observed at room temperature, which may be ascribed to quantum size effects of nanomaterials. Needle-shaped 3C-SiC nanowires may have great potential applications such as blue-green light-emitting diodes and display devices.

The one- and the two-photon absorption rates of conduction-band electrons (CBEs) in dielectric materials are calculated by second-and third-order perturbation theory, respectively. Here fused silica irradiated under 526 nm ultra-short pulse laser is used as an example. Compared with the case that only the one-photon absorption of CBE assisted by a phonon is considered. the rate of total energy gain of CBE from laser field will be enhanced by a factor of 3 when both of the one-and the two-photon absorption are included. The avalanche rate includes not only the term proportional to laser intensity, but also the terms proportional to the square of laser intensity and to the product of laser intensity and hole density. The damage threshold is calculated on the basis of the avalanche model, and find it is lowered by about 15% compared with the case for only the one-photon absorption of CBE assisted by a phonon is considered. The theoretical value agrees well with experimental results.

The rate at which conduction-band electrons (CBE) absorb laser energy is calculated by both the quantum mechanical and the classical methods. Here fused silica irradiated with a 780-nm femtosecond-pulse laser is used as an example. It is found that the rate obtained by the quantum mechanical method is about one-third of that by the classical method, and it is much less than the direct-current limit. In the flux-doubling model, the avalanche rate in fused silica is 4I ps−1 obtained by the quantum mechanical method, while it is about 13.7 I ps−1 by the classical method, where the laser intensity I is in units of TWcm−2. The differential equation of the evolution of CBE density is solved numerically, and it is found that the combination of CBE–hole recombination, CBE diffusion and initial CBE density (<1013 cm−3) is not important. The dependence of avalanche breakdown threshold on laser-pulse duration is presented. The threshold calculated by the quantum mechanical method agrees well with experimental results, while the threshold obtained by the classical method differs greatly from the experiments.