Microholes drilling has attracted extensive research efforts for its broad applications in photonics, microfluidics, optical fibers and many other fields. A femtosecond (fs) laser is a promising tool for high-precision materials processing with reduced recast/microcracks and minimized heat affected zones. But there remain many challenges in hole drilling using conventional fs laser with Gaussian beams, such as low aspect ratio and taper effects. We report small-diameter and high-aspect-ratio microholes with taper free drilling in PMMA (polymethyl methacrylate) using single-pulse fs laser Bessel beams. Axicon is used to transform Gaussian beams into Bessel beams, which then irradiate in the sample by a telescope consisting of plano-convex lens and microscope objective. Using this technique, we enhance the aspect ratio of microholes by 55 times as compared with Gaussian beams. We attribute this high aspect ratio and high quality microholes formation to the unique spatial intensity distribution and propagation stability of Bessel beams, which can effectively adjust the transient localized electron density distribution leading to a long and uniform localized-interacted zone. By using the optimized pulse energy and focal depth position, the microholes diameter ranges between 1.4-2.1 μm and the aspect ratio can exceed 460. This efficient technique is of great potentials for fabrication of microphotonics devices and microfluidics.
When a hypersonic missile with a side mounted IR seeker is launched in the atmosphere, a serious aero-optical effect is formed and affects the quality of the detector's imaging. And in the course of the missile flight time,aero-optical effects changes over time, which makes real-time, accurate correction of optical distortion becomes very difficult. Therefore, it is necessary to study the relationship between the optical distortion and time.In this paper, Fluent,a computational fluid dynamics(CFD) internet applications is used to make researches on effect of optical transmission of the flow field outside the IR window. And a thermal finite element analysis (FEA) of an IR window is used to study the aerodynamic