How to ensure the accuracy of optical glass lenses in industrial applications?

In order to ensure the accuracy of optical glass lens in industrial application, it is necessary to control it from several links:

I. Selection and inspection of raw materials

High quality optical glass material

Choose optical glass with high uniformity and low impurity content. For example, the internal stress distribution of glass materials used in high-precision optical instruments (such as mask aligner lens) should be uniform to prevent deformation during processing and use. High-quality materials have high refractive index uniformity and can provide a good foundation for subsequent high-precision processing.

The optical constants of materials (such as refractive index, dispersion coefficient, etc.) should meet strict standards. Different industrial application scenarios have precise requirements for optical constants. By controlling these parameters accurately, the lens can have stable optical performance in a specific wavelength range.

Strict inspection of raw materials

Conduct a comprehensive inspection of the purchased optical glass. Including the use of interferometer to measure the refractive index uniformity of glass, its accuracy can reach the level. To judge the internal stress by detecting the stress birefringence in the glass, it is generally required that the internal stress is within a certain allowable range to avoid affecting the lens accuracy. At the same time, the spectral transmittance of the material is analyzed by spectrometer to ensure that the material has high enough transmittance in the working wavelength range.

Second, the lens processing process control

Optimization of grinding process

Grinding is one of the key steps in the processing of optical glass lenses. Choose appropriate grinding equipment and abrasives, and the particle size and hardness of abrasives should be matched according to the lens material and accuracy requirements. For example, for high-precision aspheric lens grinding, coarse grinding can be carried out by using abrasive with coarse particles (such as tens of microns in particle size) at the initial stage to quickly remove the material surplus; In the later stage of fine grinding, fine abrasives with a particle size below several microns are used to gradually improve the surface accuracy of the lens.

During the grinding process, the grinding pressure and speed should be accurately controlled. Too much pressure will lead to scratches or deformation on the lens surface, while too little pressure will affect the grinding efficiency. The grinding speed should also be moderate. Too fast may generate too much heat, which will affect the material performance and accuracy of the lens. Generally, the grinding speed is controlled within a certain range according to the size and material characteristics of the lens. For example, for a lens with a diameter of 50mm, the grinding speed can be controlled between tens of revolutions and hundreds of revolutions per minute.

Fine management of polishing process

Polishing is an important link to improve the surface smoothness of lenses. High-precision polishing equipment, such as computer-controlled polishing machine (CCP), can accurately control the polishing path and pressure. In the polishing process, appropriate polishing solution is used, and the composition of polishing solution (such as the type and concentration of polishing powder) should be adjusted according to the lens material and accuracy requirements. For example, for high-hardness optical glass lenses, it may be necessary to use polishing solution containing high-purity cerium oxide.

The polishing time and temperature also need to be strictly controlled. If the polishing time is too long, the lens edge may be over-polished, resulting in surface errors, and if the polishing time is too short, the required surface finish cannot be achieved. Generally, the polishing temperature should be kept in a suitable range to avoid softening the lens material or generating thermal stress due to too high temperature, which will affect the accuracy. Generally, the polishing temperature can be controlled between room temperature and tens of degrees Celsius, depending on the lens material and polishing process.

Precise operation of coating process

Coating can improve the optical properties of lenses, such as antireflection film can improve the light transmittance of lenses. In the process of coating, the thickness and uniformity of coating should be accurately controlled. Advanced coating technology such as physical vapor deposition (PVD) or chemical vapor deposition (CVD) is adopted to ensure the accuracy of coating thickness by accurately controlling the parameters of coating (such as power of evaporation source, deposition time, flow rate of reaction gas, etc.). For example, for antireflection films, the thickness error should generally be controlled within a few nanometers to achieve the best antireflection effect.

The cleanliness of coating environment is very important. In the coating room, high cleanliness should be maintained to prevent impurities such as dust from mixing into the coating layer, which will affect the optical performance and accuracy of the lens. Generally, the cleanliness level of the coating room should reach 1000 or even higher, and the environment should be kept clean through an efficient air filtration system and strict personnel and equipment access management.

III. Testing and Quality Control

Use of high-precision detection equipment

The interferometer is used to detect the surface accuracy of the lens. The interferometer can detect the tiny undulation of the lens surface, and its accuracy can reach nanometer level. For example, for high-precision optical imaging lenses, the surface accuracy is required to reach a fraction of the wavelength (for example, to detect the wavelength), and the interferometer can accurately measure and provide feedback for further correction.

Using profilometer to detect the surface roughness of lens can accurately measure the irregularity of micro-geometric shape of lens surface. For lenses that need high surface finish, such as laser optical lenses, the surface roughness should generally be controlled in the range of nanometer level, and profilometer can help to determine whether the lenses meet the accuracy requirements of industrial applications.

Establishment of quality control system

Establish a perfect quality control system, including quality inspection and record of each processing link. From the inspection report of raw materials to the testing data of grinding, polishing and coating in the process of lens processing, it is necessary to record in detail. By statistical process control (SPC) and other methods, the accuracy data of lenses are analyzed, and the abnormal fluctuations in the processing process are found in time, and measures are taken to adjust and improve them. For example, if it is found that the surface accuracy of a certain batch of lenses is systematically deviated after grinding, the grinding process parameters can be traced back to find out the problems and solve them.