Erratum: Corrigendum: Fuel gain exceeding unity in an inertially confined fusion implosion

Fast path planning algorithm for large-aperture aspheric optical elements based on minimum object depth and a self-optimized overlap coefficient

In the procedure of surface defects detection of large-aperture aspheric optical elements, it is necessary to scan the surface of the element to achieve full coverage inspection. Since the curvature of the aspherical element is constantly changing from the center to the edge, it is of great difficulty to carry out efficient path planning. In addition, the machine vision system is a microscopic system with limited depth of field, and the sub-aperture imaging of aspherical elements has a visual depth along the object side. When the object depth is greater than the depth of field, out-of-focus blur will generate, so the object depth needs to be as small as possible. In response to these problems, this paper proposes a fast path planning algorithm based on the minimum object depth of a sub-aperture. To ensure minimum object depth, the machine vision system collects images along the normal direction of the sub-aperture plane. To address the problem of the surface curvatures of aspheric elements being different and the overlap coefficient difficult to determine, this paper proposes an image processing based overlap coefficient self-optimization algorithm. When scanning with full coverage of elements, there is only one connected domain in the horizontal projection image of all sub-apertures. According to this premise, the overlap coefficient is optimized through an image processing method to obtain a local optimal path planning strategy. According to the obtained path planning strategy, combining the component parameters and mechanical structure, the mapping matrix of the path planning algorithm transplanted to the detection system is calculated. Through computer programming, automatic sub-aperture acquisition is realized, and the self-edited sub-aperture stitching program is applied to reconstruct the collected sub-apertures. Our algorithm can complete path planning within 5 s, and the experimental results show that the maximum stitching misalignment error of the collected sub-apertures is no more than four pixels, and the average is one pixel. The reconstruction accuracy satisfies the needs of subsequent image processing and digital quantization.

Femtosecond x-ray streak camera based on photoelectron filter technology for laser fusion

A femtosecond x-ray streak camera based on photoelectron filter technology is reported in this paper. Photoelectrons are collimated through the slit and channel of the photoelectron filter, so that transit time spread and space charge effect of electrons are reduced. A planar-focusing high-voltage electron-optical system is designed to match the filter. The channel length of the filter is 300 μm, and the slit width is 20 μm. The streak tube using the photoelectron filter is 273 mm in length, and the extraction field value between the Au photocathode and the filter is 10 kV/mm. An experimental platform is set up to calibrate the streak camera, which is excited by a 266 nm, 130 fs UV laser. The experimental results show that temporal resolution is 357 fs and dynamic range is 182:1 of this developed camera.