3D laser-induced-damage site position is found by deep-learning method
Traditional schemes for detecting laser-induced damage in optics can directly detect and characterize damage by examining images of optical components. However, due to optical resolution, noise, shadows, and reflections, very small laser-induced damage points are not accurately characterized.
A research team from Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences (CAS) has proposed what they say is an accurate three-dimensional damage-localization method whose precision is insensitive to the type of laser damage occurring.1
The research was based on the light-diffraction rings that are produced by optical damage sites. The axial damage position of a damage site is obtained by numerically modeling the focus of the diffraction ring at the conjugate position using a method called peak distribution line (PDL) that is independent of the type of laser damage. A neural network called Diffraction-Net distinguishes the different diffraction rings arising from different surfaces and positions to obtain the lateral position.
They found that, completely trained by simulative data, Diffraction-Net could distinguish the diffraction rings even with an overlap rate lager than 61%, which they say is the best result yet reported.
In the experiments, the proposed method, for the first time, achieved the damage points on each surface of a series of large cascaded slabs (similar to those used in the laser optics at laser-fusion facilities) with the smallest laser damage site size of 8 μm. The lateral positioning error was less than 38.5 μm and the axial positioning error was less than 2.85 mm.
The researchers say that the proposed method has solved the practical inspection problems in the complex optical environment with one intensity recording, thus providing a new approach to online damage location in high-power laser system.
Source: http://english.cas.cn/newsroom/research_news/phys/202003/t20200331_231960.shtml
REFERENCE:
1. Zhan Li et al., Optics Express (2020); https://doi.org/10.1364/OE.387987.
John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.