Leonardo DRS is the industry leader for cooled and uncooled infrared sensors.

An FPA works by capturing photons falling on its detector elements. Key elements of its operation include:

1. Photon Detection: Photons from a scene are focused onto the FPA by the optical system. FPAs require collimating optics to focus the incoming energy on the plane of the detector.
2. Photoelectric Effect: Once focused on the array of diodes, the FPA becomes a photon counter.Each detector element (pixel) within the FPA absorbs these photons, causing the photoelectric effect, where photons are converted into electrons. For every photon of incident energy, the diode registers a discrete current change
3. Signal Generation: The number of electrons produced is proportional to the intensity of the incident light. These electrons are collected and generate a voltage or current signal.
4. Signal Processing: The signal is then read out from each pixel, processed, and converted into a digital form to create an image. This typically involves amplification, noise reduction, and digitization.

FPAs are typically constructed using semiconductor materials such as Mercury Cadmium Telluride (MCT) or Indium Antimonide (InSb), known for their sensitivity to infrared energy. The basic components include:

1. Detector Material: Semiconductor materials that are sensitive to the particular wavelength of interest.
2. Readout Integrated Circuit (ROIC): This is bonded to the detector array and is responsible for reading and processing the signals from each pixel.
3. Interconnects: Bonding techniques connect the detector array to the ROIC.
4. Packaging: The FPA is housed in a protective package that ensures proper thermal and mechanical stability. Because all objects radiate infrared energy, the target/scene energy must be isolated from the thermal noise associated with the packaging itself. For the detector material to begin registering usable photon information, it must be cryogenically cooled with a cooler. A Sterling cycle cryogenic cooler operates with AC power being used to alternate the polarity of the coil/pistons inside the compressor. When the coil polarity matches the magnet core polarity, the piston is forced away from the compressor center. Likewise, when the polarities are opposite the coils are forced to the center, increasing pressure. By alternating high and low pressure pulses the temperature heat removal occurs. A vacuum Dewar is used to accommodate the low operating temperature by insulating the FPA from the surrounding environment. Thermal “noise” is significantly reduced by use of coldshielding and absorptive coatings. The evacuated Dewar must operate at cryogenic temperatures. Otherwise, the water vapor present in air would form ice in the Dewar and obscure the infrared energy.
5. Optical Elements: Lenses or mirrors focus the incoming light onto the FPA, collimating the energy. The focal length of the optics is designed to be at the imaging plane of the FPA. The Dewar window and aperture define the f/n and spectral content.

Cooled infrared systems use a cryogenic cooler to reduce the temperature of the Focal Plane Array (FPA) comprised of Mercury Cadmium Telluride material. This cooling minimizes thermal noise, which allows for higher sensitivity and improved image quality. These systems typically offer superior performance in terms of resolution, detection range, and sensitivity. They are capable of detecting very small temperature differences and are ideal for long-range detection and high-precision applications such as military and aerospace.

Cooled systems are more expensive and complex due to the need for cryogenic cooling. The cooling systems add bulk and weight, and the maintenance requirements are higher compared to uncooled systems

Uncooled infrared systems operate at ambient temperatures. Instead of an FPA, the detector is a Vanadium Oxide (VOx) microbolometer that detects infrared radiation based on changes in resistance, voltage, or current as targets are heated by the incident infrared radiation. While uncooled systems have lower sensitivity and resolution compared to cooled systems, they can be very effective for mid-range and shorter-range detection. Uncooled systems are widely used in commercial, industrial, automotive, security, and military applications where size, weight, power consumption, and cost (SWaP-C) are more critical than the highest possible performance. Uncooled systems are generally less expensive, smaller, and lighter. They have fewer maintenance requirements and shorter start-up times, making them more user-friendly for a broad range of applications

Mid-Wave Infrared Advantages Include:

• Long detection ranges which can exceed 15 miles depending on the system.
• Provides better performance in environments with low to moderate humidity and temperature variations.
• Generally offers higher resolution and higher sensitivity – “seeing” very small differences in temperature in a target scene.
• Effective for imaging and detecting heat sources in a variety of atmospheric conditions. Compared to LWIR, MWIR is less affected by absorption and scattering of CO2 and water vapor in the atmosphere.
• Broad dynamic range and short integration times make MWIR well suited for tracking fast-moving targets and targets with wide temperature ranges

MWIR sensors typically require cryogenic cooling for optimal performance, making these systems more complex and expensive.

Long-Wave Infrared Advantages Include:

• Does not require cryogenic cooling, reducing system complexity and cost
• Can see through obscurants like smoke and fog
• Less complex and easier to use for general-purpose thermal imaging

LWIR systems generally have lower resolution compared to MWIR systems and can be limited in detecting and resolving finer details at longer distances.

Another significant advantage of MCT is its high quantum efficiency, which enhances the sensor’s sensitivity and ability to detect even low levels of infrared radiation. This high sensitivity is complemented by the material’s tunable bandgap. By varying the composition of mercury and cadmium, the spectral response of MCT can be customized to specific applications, allowing for tailored solutions that meet precise operational requirements.

MCT sensors are also known for their fast response times, making them perfectly suited for high-speed infrared imaging where real-time processing is critical. The high signal-to-noise ratio of MCT sensors ensures clear and accurate infrared imaging, even in low-light conditions, which is critical for many advanced imaging tasks. Additionally, MCT’s temperature sensitivity makes it ideal for temperature mapping and thermal imaging applications, providing reliable and accurate temperature readings.

The material properties of MCT also allow for the development of detectors with small pixel sizes, enhancing the spatial resolution for detailed imaging. This feature is particularly beneficial in applications requiring high-resolution images. The versatility of MCT extends to its usage in a variety of fields including military, industrial, environmental, and medical imaging, owing to its adaptability and robust performance.

Furthermore, MCT sensors demonstrate a long operational lifespan, making them a cost-effective and reliable choice for long-term where replacement or maintenance may be costly or difficult. Their integration capability is another highlight, as MCT sensors can be incorporated into complex systems, providing comprehensive solutions for advanced infrared imaging technologies.

Overall, Mercury Cadmium Telluride (MCT) offers distinct advantages for cooled infrared sensors. Its broad spectral response, high quantum efficiency, tunable bandgap, and fast response time make it an ideal material for a wide range of infrared applications, ensuring clear, accurate, and reliable imaging in even the most challenging environments.