Definition of Infrared Optics
In infrared (IR) optical systems, the primary goal is to focus a thermal image of the scene onto a detector array. Although the optical components in IR systems are similar to those in visible light systems, they must be able to transmit radiant energy within a specific wavelength range. Germanium (Ge) and zinc selenide (ZnSe) are two of the most commonly used materials in IR optics because they are able to transmit radiation in the 8-14 μm wavelength range, which is the typical operating band for thermal imaging.
The design of the lens is crucial for minimizing aberrations and internal reflections, which can degrade the quality of the thermal image. Additionally, the lens is designed to provide a field of view (FOV) that is appropriate for the intended application of the thermal imaging camera (TIC). The FOV determines the extent of the scene that can be captured by the TIC.
For TICs used by first responders, a wider FOV of around 40° to 60° is often preferred, as it allows for a larger area to be observed at once. On the other hand, TICs used for more specialized thermographic applications may have a narrower FOV, depending on the specific requirements of the user. The FOV selection depends on factors such as the desired level of detail and the distance between the camera and the target object.
By carefully selecting the appropriate materials and designing the lens, IR optical systems can effectively capture and focus thermal images onto the detector array, enabling the detection and analysis of heat patterns in a wide range of applications.
Points to note when designing infrared optical systems
1. Focal Length
A longer focal length provides higher magnification, but affects the size of the field of view, making it narrower. A shorter focal length provides a wider field of view, but at the expense of lower magnification. The choice of focal length should be determined based on specific application requirements and imaging distance. Therefore, the focal length determines the magnification and field of view of the infrared optical system.
2.Aperture
Although a large aperture can provide a lot of light and thus increase the sensitivity of the optical system, it may also introduce more aberrations. The size of the aperture also affects the depth focus range of the system. So, the aperture controls the amount of light entering the optical system.
3.Anti-Reflective Coating
Infrared optical element surfaces can be coated with anti-reflective coatings to reduce internal and external reflection losses. Anti-reflective coatings can improve a system’s transmission and image quality and reduce interference and artifacts.
4.Aberration Correction
Aberrations are common optical distortions in optical systems that can cause image distortion and blur. A well-designed infrared optical system needs to consider various aberrations, such as spherical aberration, chromatic aberration, astigmatism, etc., and take corresponding measures to correct them to improve image quality.
5.Mechanical design
The mechanical design of the infrared optical system is also important, especially in applications involving high temperatures and harsh environments. Proper mechanical design ensures the stability and reliability of optical components and provides appropriate protection and cooling measures.
The design and manufacturing of infrared optical systems is a complex process that requires comprehensive consideration of optical principles, material properties, application requirements and manufacturing processes. Through reasonable design and optimization, infrared optical systems can achieve high-quality thermal image collection and imaging, and are widely used in military, security, medical, construction, industry, scientific research and other fields.
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