Compared to visible light and other thermal bands, shortwave infrared optical lens has unique imaging advantages. They are used in electronic board inspection, material/food sorting, solar cell inspection, quality control, military applications, and industrial machine vision. Shortwave infrared optical lens is also utilized in situations where other detectors or cameras are not sensitive enough to recognize limited details.
When it comes to shortwave infrared optical lens, especially for extended band shortwave infrared lenses, the material choices need to account for factors such as wide bandwidth transmission and machinability. Therefore, materials like ZnSe, ZnS, and CaF2 have become common choices. Additionally, there are some rare glasses available. However, it is important to note that these glasses are generally not stocked and are not frequently produced. Hence, before adopting these materials, it is essential to ensure timely delivery and a steady supply.
Midwave infrared achromatic lenses are available for designers and researchers working in the 3µm to 5µm spectral region. These lenses have near-diffraction-limit performance, making them suitable for FTIR (Fourier Transform Infrared) spectroscopy, midwave infrared thermal imaging, and tunable quantum cascade lasers.
Midwave infrared optical lens is typically used in conjunction with midwave cooled detectors, with the aperture placed behind the lens. Therefore, the lenses are relatively large, and considerations such as the cold aperture effect (ghosting and reflections, also known as the cold stop effect) need to be taken into account. Though the cooled lenses and detectors are bulky, they can detect from great distances; for instance, focal lengths of 150 mm or 300 mm can observe distances of 10 km to 30 km.
LWIR lens (Longwave Infrared Lens) is typically uncooled, resulting in lower sensitivity. LWIR lens allows users to see through dust or smoke, making them particularly valuable in certain environments and applications. The field of view of the lens largely depends on the focal length and the detector size.
The design of LWIR lens is commercially driven, aiming to be both affordable and effective. Aspheric lenses are commonly used. Additionally, with the increasing commercial applications such as automotive night vision, gun sights, and mobile phones, chalcogenide glasses have become favored in these areas. Due to their ability to be molded at low temperatures, chalcogenide glass lenses can be produced in large quantities at very low costs.
In extreme cold and hot conditions, especially when there is a significant temperature difference, the curvature of the infrared lenses, the thickness of the lenses, and the refractive index of the lens barrel and lens materials change, causing the lens to defocus. To ensure clear imaging, the lens needs to be refocused, either electrically or manually. To eliminate the adverse effects of temperature changes, athermal design is required. Typically, designers will use different optical materials to achieve optical compensation (temperature difference) or use mechanical and optical material combinations that have opposing changes to achieve optomechanical compensation.
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