Sapphire, as an artificially synthesized optical material, occupies an important position in the field of optics due to its excellent physical and chemical properties. Among them, the infrared transmittance performance of sapphire lenses is particularly outstanding, making them widely used in fields that require strict infrared optical performance. This article will explore the infrared transmission characteristics, influencing factors, and practical application scenarios of sapphire lenses, and analyze the performance advantages of this special optical material for readers.

Sapphire (α - Al ₂ O3) is a single crystal aluminum oxide material, and its crystal structure determines its unique optical properties. In the infrared band, sapphire exhibits transparency. A sapphire chip with a thickness of 1mm has a transmittance of over 85% in the mid infrared region within the wavelength range of 1-5 μ m; Even in the longer wavelength range of 8-12 μ m in the far-infrared region, the transmittance can still be maintained at around 60%. This excellent infrared transmittance is attributed to the strong bonding energy of aluminum oxygen bonds in sapphire crystals, which results in an extremely low absorption coefficient in the infrared region. Compared with ordinary optical glass, sapphire has a significant advantage in transmittance in the infrared band, especially in the important atmospheric window bands of 3-5 μ m and 8-12 μ m.

The factors that affect the infrared transmittance performance of sapphire lenses mainly include crystal quality, surface processing accuracy, and coating process. In terms of crystal quality, impurity content and defect density are key indicators. High purity sapphire crystals (with impurity content below 10ppm) can significantly reduce absorption losses in the infrared band. The surface processing accuracy directly affects the scattering loss of light, and it is usually required to control the surface roughness at the nanometer level (Ra<1nm). The coating process can be tailored to specific application requirements by designing multi-layer anti reflective film systems to further enhance the transmittance of specific frequency bands. For example, in the 3-5 μ m wavelength range, an optimized anti reflection film can increase the peak transmittance of sapphire lenses to over 95%.

In practical applications, the infrared performance advantages of sapphire lenses are reflected in multiple aspects. Firstly, the wideband transmission characteristic enables it to simultaneously meet the imaging needs of visible light and infrared light. Secondly, it has excellent environmental stability. Sapphire has a Mohs hardness of 9 and its scratch resistance far exceeds other optical materials. In addition, sapphire has a high thermal conductivity (about 40W/m · K) and a low coefficient of thermal expansion (5.3 × 10 ⁻⁶/K), which enables it to maintain stable optical performance in environments with drastic temperature changes.

Industrial testing is another important application area of sapphire infrared lenses. In the semiconductor manufacturing process, sapphire windows are widely used in high-temperature process monitoring systems, which can withstand operating temperatures above 1000 ℃ without performance degradation. On the glass production line, infrared thermometers equipped with sapphire lenses can accurately measure the temperature distribution of molten glass. In addition, in laser processing equipment, sapphire protective lenses can withstand high-power laser irradiation without interfering with infrared monitoring during the processing.

With the development of infrared technology, the application prospects of sapphire lenses are even broader. In the field of autonomous driving, sapphire protective covers are applied to laser radar systems, while meeting the needs of visible light imaging and infrared sensing. In the field of consumer electronics, some smartphones have begun to use sapphire as a camera protective lens. It is worth mentioning that in space optical systems, sapphire lenses have become an ideal optical component for deep space detectors due to their good radiation resistance and low vacuum exhaust rate.

In the civilian field, the popularization of sapphire infrared lenses will bring more innovative applications. After adopting a sapphire protective cover, the security monitoring system can achieve high-definition monitoring 24/7; The use of sapphire windows in car night vision systems can significantly improve driving safety; Even in the field of household appliances, smart ovens equipped with sapphire lenses can accurately monitor the heating status of food. These applications are based on the infrared transmittance performance of sapphire.

Sapphire lenses are playing an increasingly important role in the field of optics due to their infrared transmittance, environmental resistance, and constantly improving processing technology. With the advancement of technology and the emergence of large-scale production effects, sapphire is expected to shine in a broader field of infrared optics, providing strong technical support for human exploration of the invisible light world.