Laser nuclear fusion optical parts

At present, the laser nuclear fusion device being developed in China requires a large number of high-precision, large-caliber optical components, and requires the manufacture of these optical components on time, quality and quantity. It is necessary to break through the existing technological level and adopt efficient and advanced optical manufacturing technology. Drawing on the experience of the National Ignition Facility (NIF) in foreign countries, combined with the actual situation in China, the precision machining technology is applied to the precision manufacturing of laser nuclear fusion optics.

Precision machining of large diameter planar optics

Most of the optical components in laser fusion devices are rectangular, square, and other polygonal shapes. These components have significant edge effects (especially in terms of angle) compared to circular components. At the current state of the art, it is still difficult to achieve the required transmission wavefront (PV value PeaktoValley, and peak-to-valley λ/6) and reflected wavefront (PV value, λ/4). Adopt advanced manufacturing technology. A large number of experiments have proved that the method of on-line correction grinding (Wlectrolytic In-ProcessDressing, ELID) is obviously more efficient than the traditional grinding process, which is likely to replace the traditional roughing-milling before polishing. The only drawback with coarse polishing is that the accuracy is slightly lower (compared to precision polishing).

Using a small tool to numerically polish a 340mm*340mm*60mm plane mirror, the initial reflected wavefront error is 3.5λ (PV value, λ=0.6328um). After only 30H polishing, the reflected wavefront error PV will be 0.26λ. The root mean square value is 0.035λ. As shown in the drawing (the "+, -" values listed in the ruler should be represented by different colors, black and white is just a schematic). From the figure, we can easily see the so-called "crushing" error. In high-power laser systems, such high-frequency errors must be strictly controlled, so this process cannot be used as the final processing of optical components of strong laser systems.During the experiment, we found that the accuracy of large-diameter optical components processed by continuous polishing technology can meet the requirements of engineering, but the problem is that the processing cycle is long and the dependence on people is too strong.

All of the above technologies have their own advantages and disadvantages, and cannot meet the needs of the project alone. Only a reasonable combination of these technologies can give full play to their respective advantages in order to meet the specific requirements of the project. The specific idea is to first use ELID grinding technology to precisely grind the optical component blank to within 1λ, then use the CNC machining equipment to correct the local error, process the optical component to the surface precision required by the project, and finally use the large-scale The ring polishing machine precisely polishes the optical components to the actual requirements. This process mainly solves the problems of surface roughness and waviness.

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