The optical coating is composed of thin film layers to produce interference effects to improve the transmission or reflection performance of the optical system. Its performance depends on the number of layers, the thickness of each layer and the refractive index of the interface between different layers. The most commonly used coating types in precision optics: anti-reflection coating (AR), high reflection (mirror) coating, beam splitter coating. Electron beam evaporation is a physical vapor deposition (PVD) technology that uses electron beams to directly heat evaporated materials (usually particles) under vacuum and transfer the evaporated materials to a substrate to form a thin film. Electron beam evaporation coating can produce high-purity, high-precision thin films.

Commonly used optical coating materials are as follows:

1. Magnesium fluoride: colorless tetragonal powder with high purity. It is used to prepare optical films, which can increase the transmittance without breaking points.

2. Silica: colorless and transparent crystal, high melting point, high hardness and good chemical stability. The purity is high, the high-quality SiO2 coating is prepared, the evaporation state is good, and there is no collapse point. According to the requirements of use, it can be divided into ultraviolet, infrared and visible light.

3. Zirconia: white heavy crystal, high refractive index, high temperature resistance, stable chemical properties, and high purity. It can be used to prepare high-quality zirconia coating, and it is not easy to collapse.

Electron beam evaporation applications

Electron beam evaporation is widely used in various applications due to its high deposition rate and high material utilization. For example, high-performance aerospace and automotive industries have high requirements for high temperature resistance and wear resistance of materials; durable tool hard coatings; and chemical barriers and coatings to protect surfaces in corrosive environments. Electron beam evaporation is also used in optical films, including laser optics, solar panels, glass, and architectural glass, to make them have the required conductivity, reflection, and transmission properties.

Advantages and disadvantages of electron beam evaporation

Electron beam evaporation can evaporate high melting point materials, which is more efficient than ordinary resistance heating. Electron beam evaporation can be widely used in optical films, such as high-purity films and conductive glass. It also has potential industrial applications for wear-resistant and thermal barrier coating hard coatings for the aerospace industry in the coating, cutting and tool industries. However, electron beam evaporation cannot be used to coat inner surfaces with complex geometries. In addition, degradation of the filament in the electron gun may cause uneven evaporation rates.

Electron beam evaporation workflow

Electron beam evaporation is based on the evaporation of tungsten filaments. A current of about 5 to 10 kV is passed through the tungsten wire (located outside the deposition area to avoid contamination) and heats it to the point where electron thermionic emission occurs. Permanent magnets or electromagnets are used to transfer electrons. Focus and guide the evaporated material (placed in the crucible). When the electron beam hits the surface of the evaporated particles, its kinetic energy is converted into heat, releasing high energy (more than millions of watts per square inch). Therefore, the evaporation material is contained in the furnace and must be cooled with water to avoid melting.