In the coming weeks, we will be posting about the unique design considerations and material requirements for infrared optical systems. In this post, we will focus on the definitions optical engineers use.
Infrared radiation includes electromagnetic waves with 0.75-1000 µm wavelength band. This spectral region is divided into five intervals:
Near-infrared radiation (NIR) – 0.75-1.4 µm wavelength band
Short-wavelength infrared radiation (SWIR) – 1.4-3 µm wavelength band
Mid-wavelength infrared radiation – 3-8 µm (MWIR) wavelength band
Long-wavelength infrared radiation – 8-15 (LWIR) µm wavelength band
Far-infrared radiation (FIR) – 15-1000 µm wavelength band
Original image owned by PROTHERM.
IR-radiation has a number of features that make it useful in solving specific problems. The main one is that objects with temperature above absolute zero emit IR-radiation. The intensity and spectrum (spectral concentration of a radiance) of the radiation emitted depend on the object temperature. Thermal imaging optics include optical devices that can collect and analyze object emitted IR-radiation (usually MWIR and LWIR). One such widespread device is the thermal imager.
Thermal imaging systems show the distribution of the imaged object temperature. In case of monochromatic thermal imagers, areas of a body or scene with higher temperature are brighter while cold areas are darker. In case of colored thermal imager, hot areas are red and cold areas are blue.
VIS camera works with radiation reflected from object
IR camera works with radiation emitted from object
Thermal imagers are used in many areas of science and technology such as space astrophysics, heating engineering, weather forecasting, military science, and more. Primarily, thermal imagers aid in:
Detection of the heated object on the thermal background. For example, it aids in searching for distressed people in an ocean or any other unreachable place
Exploring thermal distribution. For example, it can be used for weather exploration from space.
Read more about the optical materials appropriate for thermal and IR imaging in this link and find further details on the distinctive design features of the design of infrared optical systems in the second link.