Types and hazards of surface defects of optical components
Surface defects of optical components mainly refer to surface defects and surface contaminants. Surface defects refer to various processing defects such as pits, scratches, open bubbles, broken edges, and broken points that still exist on the surface of optical components after polishing. The main causes are the processing process or subsequent improper operation.
Here are four kinds of defects
Scratches
Refers to the long scratch marks on the surface of the optical element. Different scratch lengths can be divided into long scratches and short scratches, with 2 mm as the limit. If the scratch length is greater than 2 mm, it is a long scratch, and if it is less than 2 mm, it is a short scratch. For short scratches, the evaluation criterion is the cumulative length at the time of detection. Relatively speaking, scratches are easier to detect than pits and other defects.
Pockmark
Refers to pits, etch pits, and defects on the surface of the optical element. The surface roughness in the pit is large, the width and depth are approximately the same, and the edges are irregular. In general, defects with a length-to-width ratio greater than 4: 1 are defined as scratches, whereas defects less than 4: 1 are pitting.
bubble
It is formed by the gas that is not exhausted in time during the production or processing of the optical element. Because the pressure of the gas is evenly distributed in all directions, the shape of the bubble is generally spherical.
Broken edge
It is pointed out that the defects on the edge of the optical element are outside the effective area of the light source, but they also belong to the light scattering source, which also has a certain impact on the optical performance, so they also belong to the category of defects.
Surface defects, as a kind of microscopic local defects caused by man-made process, have a certain impact on the surface performance of optical components, which may cause serious consequences such as operation errors of optical instruments. In short, the surface defects of optical components will harm the performance of the optical system, and the fundamental reason is the light scattering characteristics.
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Hazardous performance of surface defects of optical components
(1) The quality of the beam is degraded. Defects on the surface of the component will produce light scattering effects, which will consume a large amount of energy after the beam passes through the defect, thereby reducing the quality of the beam.
(2) Thermal effect of defects. Because the area where the surface defect is located is easier to absorb more energy than other areas, the resulting thermal effect may cause local deformation of the component defect, damage the film layer, etc., and thus harm the entire optical system.
(3) Damage other optical components in the system. In the laser system, under the irradiation of high-energy laser beams, the scattered light generated by the defects on the surface of the component will be absorbed by other optical components in the system, resulting in uneven light reception of the component.When the damage threshold of the optical component material is reached, it will The quality of the propagating light is affected, the optical components are damaged, and the optical system is more likely to be seriously damaged.
(4) Defects can affect the visual field cleanliness. When there are too many defects on the optical components, it will affect the microscopic aesthetics. In addition, the defects will also leave tiny dust, microorganisms, polishing powder and other impurities, which will cause the components to be corroded, mildew, fog, Will significantly affect the basic performance of the component.
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The detection of the surface shape error and surface roughness of optical components is the focus of the research field of optical inspection technology. Since the quality of the surface of optical components directly affects the performance of the entire optical system, I want to make optical instruments and equipment work more efficiently. Not only need to pay attention to the surface quality of optical components during processing, but also the inspection of finished components can not be ignored.