1. Characteristics of sapphire windows

(1) Optical properties

It boasts excellent transmittance in the ultraviolet, infrared and visible light wavelengths, with a light transmission range from approximately 190nm of ultraviolet light to around 5000nm of mid-infrared light. It is capable of transmitting wavelengths from 200nm to 5500nm and it is compatible with ultraviolet, visible and near-infrared light.

(2) Mechanical properties

Its Mohs hardness of approximately 9, second only to that of diamond, provides excellent wear and scratch resistance. The compressive strength of the material can reach 2000Mpa, the flexural strength is 1540Mpa, and the Young’s modulus of elasticity is 345GPa. It is characterized by its high strength and ability to be manufactured with strict tolerances and thicknesses.

(3) Thermal properties

It is able to function efficiently in temperatures ranging up to 2030°C while retaining its structural and optical characteristics in extreme heat, and boasts exceptional thermal conductivity even at lower temperatures.

(4) Chemical properties

It is capable of withstanding the impact of acids and alkalis up to 1000 degrees Celsius, while also demonstrating resistance to the influence of hydration and weathering. Furthermore, it exhibits strong corrosion resistance and can effectively function in corrosive environments over extended periods.

2. Application domains

(1) Military field

It is utilized in the fields of night vision, infrared and far-infrared sights, night vision cameras and other equipment, as well as satellite technology, aerospace instruments and metrology. It is able to maintain stable optical performance in complex and harsh military environments, providing clear vision and accurate signal transmission for military equipment.

(2) Aerospace field

As infrared and ultraviolet windows for aerospace instruments, they can withstand extreme temperature and pressure changes at high altitudes, as well as radiation and micrometeoroid impacts in the space environment, ensuring the normal operation of the instruments and equipment and the observation of the external environment.

(3) Industrial field

For instance, pressure-resistant windows are used in scenarios such as high-pressure reactors, deep water, geological rock exploration, the chemical industry and vacuum containers. These windows are characterized by their high strength and corrosion resistance, which makes them ideal for use as reliable observation windows for equipment in harsh conditions, such as high pressure and high corrosiveness.

(4) Scientific research field

It is suitable for a variety of window materials, including those used in low-temperature experimental observation ports and high-intensity lasers. In laser experiments, it can withstand the impact of high-energy lasers, ensuring the transmission of lasers and the safe conduct of experiments. In low-temperature experiments, its excellent performance at low temperatures facilitates accurate observation of experimental phenomena.

(5) Medical field

Sapphire components are ideal for use in certain medical devices, such as laser treatment equipment and optical diagnostic instruments, where high-precision and high-stability optical components are required. In addition, the enhanced corrosion resistance of these materials facilitates easier cleaning and disinfection of the equipment.

(6) Electronic field

Sapphire windows are used in the manufacturing process for screens or protective windows of electronic products, including mobile phones and watches. For instance, the watch screen, with its high hardness and wear resistance, can effectively prevent surface scratches and maintain good visibility.

3. Manufacturing technique

(1) Crystal growth

The predominant methods encompass the pulling method and the soaking method, among others. The precise control of growth conditions, such as temperature and atmosphere, is pivotal in the synthesis of high-quality sapphire crystals.

(2) Cutting

The use of diamond cutting tools and similar apparatus allows for the precise cutting of grown sapphire crystals into the required sizes and shapes, including circular, rectangular, and stepped forms.

(3) Grinding and polishing

The process of grinding and polishing the cut sapphire windows is of paramount importance in achieving the requisite surface finish and flatness.

(4) Coating

In accordance with the specific application requirements, it is possible to coat anti-reflection films, reflective films and similar materials on the surface of sapphire windows. This process enhances their optical performance.

Advances in technology have enabled the development of sapphire windows that are larger, more pure and less stressed. Research into connection technology is ongoing, and the results of this research are providing a new approach to the manufacturing of large-sized sapphire windows. It can achieve the basic homogeneity and isolation of the joint and base material, improving the light transmittance and mechanical properties of the joint.