Thermal imaging cameras convert thermal (heat) energy to visible light for analysing an object. The image produced is known as a thermogram and is analysed through thermography. Therefore, thermal imaging cameras show a picture showing the temperature difference of a surface.
A new interest in Chalcogenide glasses has arisen as a result of an emerging set of potential applications and increased interest in infrared (IR) designs that are smaller, lighter, and do not require rather expensive internal cooling systems.
Typically, the lenses used in thermal imaging are made from expensive single-crystal materials such as Ge and ZnS via the single point diamond turning method.
Chalcogenides are characterised by high refractive index values, transparency in the IR region, and reduced cost because IR lenses can be fabricated by the compression moulding method.
Depending on the composition of the chalcogenide glasses, band-passes ranging from the visible spectrum to 15 μm wavelengths exist, making them suitable for both mid-wave (MW) and long-wave (LW) IR applications with low dn/dT and low dispersion properties.
Based on applications, the IR spectrum has been divided into three regions: short-wave (SW) IR, mid-wave MWIR and long-wave LWIR.
SWIR: This wavelength is not visible to the human eye and tends to produce the clearest images because photons are reflected, absorbed, and scattered by objects, creating the high contrast needed for a strong resolution.
The most commonly used sensors for detecting SWIR are indium gallium arsenide or mercury cadmium telluride. These sensors are expensive, so SWIR applications are typically concentrated in high-value areas, such as anti-counterfeiting, solar cell inspection, process quality control, medical imaging, identifying and sorting, etc.
The Apple Looks Perfectly Red with Visible Imaging. Bruising is evident on the apple with SWIR imaging.
MWIR: Medium-wave infrared thermal cameras, also known as cooled thermal cameras, can detect sudden temperature fluctuations and avoid scattering from atmospheric conditions. They are highly suitable for long-range applications in challenging weather conditions.
However, since they require internal cooling, they are considerably more expensive. But, their superior range and performance allow them to deliver results that uncooled thermal cameras cannot achieve.
A comparison between the Visible, SWIR and MWIR images
LWIR: Long-wave infrared cameras, also known as Uncooled Thermal Cameras, have the broadest range of applications, particularly in the civil security sector. They generally measure the surface temperature profiles of objects with high accuracy making heat radiation visible from greater distances or even in darkness.
Although the image resolution may be quite poor, this does not disqualify them from applications like building inspection, thermal imaging surveillance, personal night vision, search and rescue tools for firefighters, and other low-cost uncooled systems.