Industry Application | Application of Atometrics white light interferometer in the field of optical lenses

With the development of science and technology, optical lenses are widely used in people's daily life. Improving the product quality and performance of optical lenses plays a vital role in enhancing the competitiveness of the modern optical industry. To improve the product quality and performance of optical lenses, we must not only rely on advanced processing technology, but also rely on precision testing technology. Parameters such as surface roughness, surface shape, and radius of curvature are important factors affecting the quality control and performance of optical lenses. Choosing a high-precision, fast, and easy-to-operate detection method can help reduce the scrap rate of optical lenses and further enhance the competitiveness and core technology of the optical lens industry.

1. Classification of optical lenses:

According to the shape of the lens, it can be divided into two categories: spherical lenses and aspherical lenses.

1. Spherical lens refers to a lens with one side being spherical and the other side being flat, or both the inner and outer sides being spherical. Spherical lenses are generally divided into concave lenses and convex lenses. Spherical lenses will have aberrations, so aspherical lenses that can reduce, supplement, and correct aberrations and distortions came into being.

2. Aspherical lenses are lenses whose radii at each point on the surface are different due to multi-image high-order equations, and the curvature of the lens surface is not completely circular. This type of lens can improve the image quality, expand the field of view, and improve the performance of the optical system by correcting multiple aberrations in the optical system, thereby improving the identification ability of the optical system. One or several aspherical lenses can replace many spherical lenses, thereby reducing the production cost of the product, simplifying the product production process and structure, and reducing the weight of the optical product to a certain extent. At present, aspherical surfaces have gradually become one of the most widely used optical components in optical products.

• Aspheric technology is generally used in optical instruments such as high-end cameras, astronomical telescopes, precision microscopes, and optical measuring instruments to make their imaging clearer and more accurate.

• In the field of semiconductor lasers and optical fiber communications, aspheric technology can improve the focusing and coupling efficiency of light beams, and improve the performance and stability of equipment.

• In the field of medical devices, aspheric lenses can achieve precise positioning and focusing of laser beams, improve the accuracy and safety of laser surgery; they can also be used in the manufacture of medical devices such as artificial lenses and eyeglass lenses to improve the effect and comfort of vision correction.

• In the field of aerospace, aspheric lenses can improve the imaging accuracy and stability of space optical equipment such as satellites and telescopes, and adapt to extreme space environments. In aviation devices such as aircraft and missiles, aspheric technology can also improve the performance of optical guidance systems and improve the accuracy of navigation and guidance.

2. Precision measurement requirements for optical lenses:

Surface roughness refers to the unevenness of the surface with small spacing and tiny valleys. The smaller the surface roughness, the smoother the surface of the object. Sa refers to the "arithmetic mean of the absolute value of the profile deviation of all peaks and valleys" within the sampling area.

Surface shape refers to the shape and curvature of the surface of an optical lens. Different surface shapes will have different effects on the propagation and focusing of light. In the field of optics, the indicator of the surface quality of an optical surface is generally the PV value, also called the peak-to-valley value, which generally indicates the deviation between the actual surface of the lens and the ideal spherical surface. It is a more comprehensive surface error indicator. Generally speaking, the smaller the PV value, the smoother the surface of the object and the higher the processing quality.

The radius of curvature refers to the distance between the vertex and the center of curvature of an optical lens, and is an important parameter in the research and development and production of optical components. Through the precise measurement of the radius of curvature, the optical path length when the light passes through the lens can be determined, thereby helping the parameter requirements of each stage of research and development, production and quality control monitoring.

In order to achieve the expected accuracy standard of optical lenses, multiple precision measurements and shaping will be carried out during the processing of optical lenses to detect whether they meet product quality standards. Through multiple iterations of grinding, polishing and other techniques, the product accuracy, quality and performance of optical lenses can be improved. Therefore, precision measurement is an indispensable step in the research and development, production and manufacturing of optical lens products.

(1) Ultra-smooth processed components:

In the field of precision optics, components with Ra values less than 0.3nm are generally called ultra-smooth (ultra-smooth) components. In optical systems, ultra-smooth processed components effectively reduce light scattering by virtue of their extremely low surface roughness and lossless surface characteristics.

The following is an example of measuring the surface roughness of an ultra-smooth lens:

Surface roughness measurement

(2) Microlens:

Microlens is a common micro-optical element used to gather and diverge light radiation in optical systems. Microlens array is an array structure composed of multiple microlenses. It not only has the basic functions of traditional lenses such as focusing and imaging, but also has the advantages of high integration and small unit size. This structure can achieve efficient control and processing of light and is widely used in optical communications, optical imaging, laser processing and other fields.

The following is a measurement example of the surface roughness, curvature radius, and surface shape PV value of the microlens matrix:

Roughness(Ra), radius of curvature(R) and surface shape(PV) measurement

(3) Fresnel lens:

Fresnel lens, also known as threaded lens, has a smooth surface on one side and a series of concentric circles engraved on the other side from small to large. This concentric circle texture is designed based on the requirements of light interference, perturbation, relative sensitivity and receiving angle.

Fresnel lens is widely used and is often used in precision optics, polymer materials, mechanical processing, aviation and navigation, infrared detection, smart electronic products, focusing and energy, new energy photovoltaics and other fields.

The following is an example of measuring the curvature radius and surface shape PV value of Fresnel lens:

Radius of curvature(R) and surface shape(PV) measurement

(4) Cylindrical mirror:

Cylindrical mirror is a special aspherical lens with special optical properties such as changing the image size. It can effectively reduce chromatic aberration and spherical aberration and is widely used in various optical products. With the development of science and technology, the requirements for cylindrical mirror parts are getting higher and higher. At this time, precision measurement technology plays a key role.

The following is a measurement example of the curvature radius and surface PV value of the cylindrical mirror:

Radius of curvature(R) and surface shape(PV) measurement

(5) Concave mirror and convex mirror:

A concave mirror is a spherical mirror that uses the inner side of the sphere as the reflective surface, and a convex mirror is a spherical mirror that uses the outer side of the sphere as the reflective surface. Concave mirrors converge light and are often used in products such as satellite antennas, radars, lamps, and telescopes; convex mirrors diverge light and are often used in products that need to expand the field of view, such as turning mirrors and wide-angle mirrors.

The following is an example of measuring the surface roughness and PV value of a concave mirror:

Surface roughness(Ra) and shape(PV) emasurement

The AM-7000 series of Atometrics white light interferometers have sub-nanometer accuracy.

The highest RMS repeatability can reach 0.002nm, and with a large range of piezoelectric ceramic devices, the maximum scanning speed is 400μm/second.

3200Hz plus the industry's first SST+GAT algorithm can instantly complete up to 5 million point cloud acquisition.

The white light interferometer is based on the principle of white light interference. Through optical interference phase measurement, the detection accuracy of less than 1nm can be obtained at any magnification.

Covering the commonly used international standard measurement tools on the market, it can easily analyze 3D data with high efficiency and can easily cope with applications in various industries.

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