Laser-induced periodic surface structure (LIPSS) is a universal phenomenon which occurs for both continuous laser and pulsed laser. Recently, most studies are focus on LIPSS irradiated by fs laser. However, LIPSS irradiated by continuous laser still need to be carefully studied. Here, We study LIPSS in silicon wafer irradiated by continuous laser for different duration time and power. For the same power, we can observe the evolution process of LIPSS for different time. It is surprising that the evolution process of LIPSS seems to be layered, which occurs for different power. The inner layer occurs at first, then the outer layer occurs. Our study can be used to control the formation of LIPSS.
The photoelectric parameters degradation of Si-based PIN photodiodes irradiated by 1064 nm millisecond Nd:YAG laser has been measured. The samples were the commercial silicon PIN photodiodes BPW34 with plastic package. The applied laser fluence levels range from 20J/cm<sup>2</sup> to 1400J/cm<sup>2</sup>. Surface damage morphology, dark current and sensitivity were investigated for the irradiated photodiodes. It has been shown that the dark current was the first and the most sensitive degradation parameter, and we believe that the dislocation introduced by the tangential component of thermal stress in the  and  direction was the main reason. The sensitivity decrease until the dark current reach to μA magnitude and the surface have melted seriously, the finite element method was used to calculation the dopant redistribution process. It shows that the degradation of sensitivity depends greatly on the process under various applied laser fluencies.
Laser propulsion in air or vacuum has been developed as a thruster technology for the attitude control of micro class satellites. Laser propulsion in water can be used as a technology for propelling underwater platform or controlling microfluid device. Laser propulsion effects in water are much better in air due to the force from laser-induced bubble in water. The target geometries will influence the propulsion effects in air. In order to investigate the influence of target geometries on laser propulsion in water, targets with/without conical cavity and hemispherical cavity are designed in this paper. The momentum<i> I<sub>T </sub></i>gained by targets and the momentum coupling coefficient <i>C<sub>m</sub></i> are investigated experimentally by high-speed photography method. It shows that the propulsion effects are better if there is a cavity on the laser irradiated surface of the target, and a hemispherical cavity works better than a conical cavity. In addition,<i> I<sub>T</sub></i> increases with the laser energy, but the increasing trend slows gradually, and <i>C<sub>m</sub></i> increases with the laser energy first, and then levels off for all four targets. These results are both due to the laser plasma shielding. In conclusion, we need design suitable target geometries and use optimal laser energy to get the best propulsion effect for controlling microfluid device or micro class satellites.