rus
Solution of many problems of various human activities require special-propose machinery and devices that enhance fundamental sensory organs physical capacities. Design office ViTA’s produced serial and customized short-wave IR cameras belong to this devices.
Теги: detection of laser designators night vision short-wave infrared (swir) light swir-излучение target recognition ночное видение обнаружение лазерных целеуказателей обнаружение целей
Detecting different types of radiation
In everyday life, we encounter electromagnetic radiation in many different forms such as visible light, ultraviolet light, radio waves or X-rays, differing only in their wavelengths. Within the electromagnetic spectrum, infrared radiation is located between visible light and microwaves.
All physical objects constantly emit infrared radiation. Once an object becomes hotter, it emits a more intense radiation at shorter wavelengths. At moderate temperatures (above 25 °C), the intensity of the radiation reaches a level that we can detect as heat.
At temperatures above 800 °C, the intensity is high enough and the wavelength short enough for the radiation to pass the threshold at the red end of the visible light spectrum. Hence, steel glows red upon heating and becomes white the hotter it gets.
This means that IR radiation and likewise heat can be detected and measured with cameras calibrated accordingly.
What is SWIR?
Short-wave infrared (SWIR) light is typically defined as light in the 0.9–1.7µm wavelength range, but can also be classified from 0.7–2.5µm. Since silicon sensors have an upper limit of approximately 1.0µm, SWIR imaging requires unique optical and electronic components capable of performing in the specific SWIR range. Indium gallium arsenide (inGaAs) sensors are the primary sensors used in SWIR imaging, covering the typical SWIR range, but can extend as low as 550nm to as high as 2.5µm.
Unlike Mid-Wave Infrared (MWIR) and Long-Wave Infrared (LWIR) light, which is emitted from the object itself, SWIR is similar to visible light in that photons are reflected or absorbed by an object, providing the strong contrast needed for high resolution imaging. Ambient star light and background radiance (nightglow) are natural emitters of SWIR and provide excellent illumination for outdoor, nighttime imaging.
InGaAs sensors can be made extremely sensitive, literally counting individual photons. Thus, when built as focal plane arrays with thousands or millions of tiny point sensors, or sensor pixels, SWIR cameras will work in very dark conditions. Night vision goggles have been around for several decades and operate by sensing and amplifying reflected visible starlight, or other ambient light, in what are called image intensification (I-Squared) tubes. This technology has worked well for direct view night vision goggles. But when an image needs to be sent to a remote location (an intelligence center, for example), there is no practical method which does not introduce reliability and sensitivity limitations (e. g. I2CCD). Because all of SUI’s SWIR sensors convert light to electrical signals, they are inherently suitable for standard storage or transmission techniques.
But aren’t there other cameras that operate in the shortwave infrared range? Yes, sensors constructed from materials like mercury cadmium telluride (HgCdTe) or indium antimonide (InSb) can be very sensitive in the SWIR band. However, in order to increase their signal-to-noise ratio to usable levels, these cameras must be mechanically cooled, often to extremely low temperatures. In large military aircraft designed for surveillance and reconnaissance, cooling is not a problem since these platforms are designed with plenty of space and power to run mechanical cooling systems. In stark contrast, similar sensitivity can be achieved at room temperatures with a Sensors Unlimited InGaAs camera.
Essentially, InGaAs cameras can be small and use very little power, but give big results. InGaAs found early applications in the telecom industry because it is sensitive to the light used in long distance fiber optics communications, usually around 1550 nm.Sensors Unlimited’s InGaAs diodes and arrays continue to be used in telecom, often in Optical Power Monitors that employ spectrometers operating in the SWIR band. Surprisingly, interesting capabilities have resulted from this combination. By using SWIR illumination like 1.55 micron lasers or LEDs, it is possible to covertly illuminate a scene that can be viewed only with SWIR cameras. So, imagine a military truck able to temporarily illuminate its path when nightglow is not available (for instance, a road under thick tree branches or in a tunnel) in order to safely navigate a route in hostile territory. SUI InGaAs cameras are of great value in such applications. And because such illuminators are eye safe, there are few restrictions on how they are used.
It is essential to use a lens that is designed, optimized, and coated for the SWIR wavelength range. Using a lens designed for the visible spectrum will result in lower resolution images and higher optical aberrations. Since SWIR wavelengths transmit through glass, lenses, and other optical components (optical filters, windows, etc.) designed for SWIR can be manufactured using the same techniques used for visible components, decreasing manufacturing cost and enabling the use of protective windows and filters within a system.
A large number of applications that are difficult or impossible to perform using visible light are possible using SWIR. When imaging in SWIR, water vapor, fog, and certain materials such as silicon are transparent. Additionally, colors that appear almost identical in the visible may be easily differentiated using SWIR.
So, Why SWIR?
High sensitivity
High resolution
Seeing in the light of night glow or night sky radiance
Day-to-night imaging
Covert illumination
Able to see covert lasers and beacons
No cryogenic cooling required
Conventional, low-cost visible spectrum lenses
Small size
Low power
SWIR camera technology
The invisible light
Sensors used in SWIR cameras work similar to silica based CCD or CMOS sensors by converting photons into electrons – so called quantum detectors. But to be able to detect light be- yond the visible spectrum, their photon sensitive area is made of materials such as Indium Gallium Arsenide (InGaAs) or Mercury Cadmium Telluride (MCT – HgCdTe). Thereby, in dependency of the material composition (chemical structure), these sensors are sensitive in different wavelength ranges and might require a strong cooling to achieve a proper SNR ratio (sometimes down to cryogenic temperatures using liquid nitrogen or a small Stirling cycle refrigerator unit).
In contrast to silicium-only based CCD and CMOS sensors, an InGaAs sensor is made of different materials. Combining these materials is a relative complex and time consuming technology, as many manufacturing steps are needed. Additionally, theproduction yield is relatively low. This is mainly caused by difficulties that may occur when connecting the CMOS read-out circuit with the photosensitive part of the sensor. All this makes these sensors types quite expensive.
Two other points may be of interest: Currently, it is impossible to combine the ROIC (read-out circuit) with the photosensitive area with 100% accuracy. Therefore, these sensors have a much higher percentage of defective pixels than CCD or CMOS sensors, which makes a proper image correction in the camera inevitable. Moreover, the thickness of the Indium Phosphide (InP) layer determines the spectral sensitivity range of the sensor. The thinner it is, the more light with higher energy can pass through.
Moisture Detection
Water absorbs strongly at wavelengths of 1450 nm and 1900 nm. By using a corresponding filter or lighting, this feature can be used for various inspection tasks:
Verification of coatings or dryness uniformity in bulk material
Fill level detection through non-transparent containers
Detection of damaged or bruised fruit
Gauging relative water content in plants
Items with higher water distribution will appear darker than drier ones.
The technique described is usable in many industries like:
Food & beverage, agriculture
Mining
Woodworking and lumber
Textile and clothing
Automotive
Short-wave infrared cameras enable various types of new appli- cations or enhance current machine vision systems by imaging beyond the visible spectrum.
As an example, SWIR cameras are often able to "see" through surfaces that are non-transparent to the human eye. This feature helps to visualize underlying features such as fill levels, hidden moisture, or tamper-proof security codes.
In contrast to MWIR cameras, SWIR cameras do not always require sensor cooling. In addition, no special lenses are needed as wavelengths between 900 nm to 2700 nm can pass through glass. All this helps to keep the overall system costs at a moderate level.
Additionally the usage, the use of filters, wavelength disper- sive optics, or monochromatic light sources are convenient to capture a distinct and a measurable contrast of the inspected object.
Defense applications for SWIR InGaAs cameras
Key performance indicators:
SWIR InGaAs imagers are sensitive to nightglow (1 to 1.6 µm)
SWIR InGaAs cameras can be uncooled, small, lightweight and low-power
Covert and eye-safe lasers, e. g., at 1550 nm, can be used to illuminate targets
Unlike LWIR and MWIR imagers, SWIR imagers see reflected light. SWIR InGaAs cameras offer unique capabilities, complementary to LWIR and MWIR cameras.
Detection of laser designators
Many applications exist for lasers on the modern battlefield: range-finding lasers are used to detect the range of an object whereas target designator lasers are used for attack.
The most common military lasers operate around 850 nm, 1060 nm, or 1550 nm. The first two types are visible to night vision goggles; the third one, 1550 nm, is therefore considered covert. SWIR InGaAs cameras are able to see all three at the same time.
Nightvision and target recognition
Thermal imaging cameras, such as LWIR uncooled microbolometer cameras, have excellent detection abilities at night. SWIR InGaAs cameras however, are a good complement to thermal imaging cameras.
While thermal imaging can easily detect the presence of a warm objects, e. g., cars, trucks, people etc.., in a cooler environment, a SWIR camera can be used to identify and recognize those objects.
SWIR nightvision is based on reflection of infrared rays from atmospheric glow or nightglow rather than on thermal radiation. Therefore, SWIR images are close representations of what is seen in the visible spectrum. Compared to thermal imagers, SWIR InGaAs cameras also have a better dynamic range.
Thermal imagers are another class of camera with good detection abilities. Sensors Unlimited often recommends that such imagers are a good compliment to SWIR. While thermal imaging can detect the presence of a warm object against a cool background, a SWIR camera can actually identify what that object is. That’s because thermal imagers do not provide the resolution and dynamic range of imaging possible with an InGaAs SWIR focal plane array. In the military world, the serious problem of determining whether a threatening vehicle is a civilian truck or a military tank is crucial. SWIR can help with this friend-or-foe determination.
CMOS and CCD imagers are excellent devices that continue to evolve to meet military needs. But such sensors are typically just daylight sensors. On the other hand, a single SWIR camera can be used for both day and night imaging.
Obviously, a VISNIR InGaAs camera benefits from its ability to see more wavelengths when there is some visible light present, for example from street lights or urban glow. Additionally, by using SWIR illumination for example 1550 nm LEDs or lasers, a scene can be covertly illuminated, i. e., viewing is only possible with a SWIR camera. Moreover, SWIR lasers are eye-safe, i. e., they can be used to safely illuminate targets and humans.
Laser gated imaging
Laser gated imaging allows for imaging at long distances while reducing the effect of obscurants in the atmosphere. In laser gated imaging, a pulsed laser is used to illuminate the scene while the reflected light is detected by a camera with a short exposure or gating time. The exposure is delayed so imaging occurs at a particular distance, thus the image is only from the reflection of objects at that distance. When using a SWIR InGaAs camera, covert and eye-safe pulsed lasers can be used.
Situational awareness – gunshot detection
Acoustic sensors that "listen" to the shockwave of a bullet are not the only solution for gunshot
detection. Gunshot signature can be identified, located and processed even faster using high-speed SWIR InGaAs cameras, either at night or during daytime. The combustion gases and hot debris projected from the gun upon firing are detectable.
Seeing through haze, smoke and fog
Compared to visible cameras, SWIR InGaAs cameras offer superior performance in imaging through dust, fog, haze or smoke In case of fire, the location of the flames can easily be found.
Spectroscopic Analysis
Unique molecular absorbance of light is not only evident in the MWIR spectrum, but also at shorter wavelengths in the SWIR, NIR, and visible spectrum. Hence, the spectral response can be collected either by acquiring the reflected or transmitted light.
Spectroscopy is non-destructive and requires no sample prepa- ration in general. Therefore, many material attributes can be measured rapidly in-line for qualitative as well as quantitative parameters.
Applications are:
Structural clarification of unknown substances
Categorization of purity of substances by quantitative definition
Probing of bulk material with minimum sample preparation (Chemometrics)
Determination of chemical classification numbers
Quality analysis of agricultural products
Plastics sorting
Semiconductor/Solar Cell Inspection
In the wafer and solar cell production, electroluminescence (light emission as a response to electric current) is used espe- cially in the final production step of quality inspection to detect micro-cracks and printing problems. Whereas, photolumines- cence (light emission as a response to light) can be applied throughout the entire manufacturing process. SWIR cameras are most qualified for these tasks because the light emitted by silicon has a peak at 1150 nm. Moreover, the quantum efficiency of InGaAs sensors is much higher towards NIR-enhanced cooled or uncooled CCD and CMOS cameras that are sensitive up to ~1000 nm.
Additionally, at wavelengths below 1150 nm silicon is non-trans- parent. Thus, SWIR cameras are perfect for analyzing metall- ization and electrical contact errors on the backside of wafers.
Further Applications
Metal and glass industry: Thermal imaging of hot objects (ranging from of 250 °C to 800 °C)
Medical, science, and biology: Laser gauging
Print industry: Banknotes inspection
Art inspection
Vision enhancement
Near/Short wave Infrared Sensors for Optical Coherence Tomography (OCT) High Resolution Imaging in Tissue
Optical Coherence Tomography (OCT), a low-coherence interferometry technique, is well established as a non-invasive clinical tool for high resolution ophthalmic imaging of the retina. By using the 1.05 µm central wavelength, instrumentation companies are now developing systems to image deeper through the retina into the blood vessel layer (called the choroid) to diagnose eye diseases and monitor treatment. Developing clinical applications are in Endoscopy, both in the esophagus or in the arteries, and dentistry.
Image Through Glass
Finally, one major benefit of SWIR imaging that is unmatched by other technologies is the ability to image through glass. Meaning, cameras can use conventional, cost-effective visible camera lenses for all but the most demanding applications. For SWIR cameras, special expensive lensing or environmentally hardened housings are mostly unnecessary – making them available for a wide variety of applications and industries. This ability also allows for the shortwave IR camera to be mounted inside a protective window, providing extra flexibilty when positioning the camera system on a potential platform.
In everyday life, we encounter electromagnetic radiation in many different forms such as visible light, ultraviolet light, radio waves or X-rays, differing only in their wavelengths. Within the electromagnetic spectrum, infrared radiation is located between visible light and microwaves.
All physical objects constantly emit infrared radiation. Once an object becomes hotter, it emits a more intense radiation at shorter wavelengths. At moderate temperatures (above 25 °C), the intensity of the radiation reaches a level that we can detect as heat.
At temperatures above 800 °C, the intensity is high enough and the wavelength short enough for the radiation to pass the threshold at the red end of the visible light spectrum. Hence, steel glows red upon heating and becomes white the hotter it gets.
This means that IR radiation and likewise heat can be detected and measured with cameras calibrated accordingly.
What is SWIR?
Short-wave infrared (SWIR) light is typically defined as light in the 0.9–1.7µm wavelength range, but can also be classified from 0.7–2.5µm. Since silicon sensors have an upper limit of approximately 1.0µm, SWIR imaging requires unique optical and electronic components capable of performing in the specific SWIR range. Indium gallium arsenide (inGaAs) sensors are the primary sensors used in SWIR imaging, covering the typical SWIR range, but can extend as low as 550nm to as high as 2.5µm.
Unlike Mid-Wave Infrared (MWIR) and Long-Wave Infrared (LWIR) light, which is emitted from the object itself, SWIR is similar to visible light in that photons are reflected or absorbed by an object, providing the strong contrast needed for high resolution imaging. Ambient star light and background radiance (nightglow) are natural emitters of SWIR and provide excellent illumination for outdoor, nighttime imaging.
InGaAs sensors can be made extremely sensitive, literally counting individual photons. Thus, when built as focal plane arrays with thousands or millions of tiny point sensors, or sensor pixels, SWIR cameras will work in very dark conditions. Night vision goggles have been around for several decades and operate by sensing and amplifying reflected visible starlight, or other ambient light, in what are called image intensification (I-Squared) tubes. This technology has worked well for direct view night vision goggles. But when an image needs to be sent to a remote location (an intelligence center, for example), there is no practical method which does not introduce reliability and sensitivity limitations (e. g. I2CCD). Because all of SUI’s SWIR sensors convert light to electrical signals, they are inherently suitable for standard storage or transmission techniques.
But aren’t there other cameras that operate in the shortwave infrared range? Yes, sensors constructed from materials like mercury cadmium telluride (HgCdTe) or indium antimonide (InSb) can be very sensitive in the SWIR band. However, in order to increase their signal-to-noise ratio to usable levels, these cameras must be mechanically cooled, often to extremely low temperatures. In large military aircraft designed for surveillance and reconnaissance, cooling is not a problem since these platforms are designed with plenty of space and power to run mechanical cooling systems. In stark contrast, similar sensitivity can be achieved at room temperatures with a Sensors Unlimited InGaAs camera.
Essentially, InGaAs cameras can be small and use very little power, but give big results. InGaAs found early applications in the telecom industry because it is sensitive to the light used in long distance fiber optics communications, usually around 1550 nm.Sensors Unlimited’s InGaAs diodes and arrays continue to be used in telecom, often in Optical Power Monitors that employ spectrometers operating in the SWIR band. Surprisingly, interesting capabilities have resulted from this combination. By using SWIR illumination like 1.55 micron lasers or LEDs, it is possible to covertly illuminate a scene that can be viewed only with SWIR cameras. So, imagine a military truck able to temporarily illuminate its path when nightglow is not available (for instance, a road under thick tree branches or in a tunnel) in order to safely navigate a route in hostile territory. SUI InGaAs cameras are of great value in such applications. And because such illuminators are eye safe, there are few restrictions on how they are used.
It is essential to use a lens that is designed, optimized, and coated for the SWIR wavelength range. Using a lens designed for the visible spectrum will result in lower resolution images and higher optical aberrations. Since SWIR wavelengths transmit through glass, lenses, and other optical components (optical filters, windows, etc.) designed for SWIR can be manufactured using the same techniques used for visible components, decreasing manufacturing cost and enabling the use of protective windows and filters within a system.
A large number of applications that are difficult or impossible to perform using visible light are possible using SWIR. When imaging in SWIR, water vapor, fog, and certain materials such as silicon are transparent. Additionally, colors that appear almost identical in the visible may be easily differentiated using SWIR.
So, Why SWIR?
High sensitivity
High resolution
Seeing in the light of night glow or night sky radiance
Day-to-night imaging
Covert illumination
Able to see covert lasers and beacons
No cryogenic cooling required
Conventional, low-cost visible spectrum lenses
Small size
Low power
SWIR camera technology
The invisible light
Sensors used in SWIR cameras work similar to silica based CCD or CMOS sensors by converting photons into electrons – so called quantum detectors. But to be able to detect light be- yond the visible spectrum, their photon sensitive area is made of materials such as Indium Gallium Arsenide (InGaAs) or Mercury Cadmium Telluride (MCT – HgCdTe). Thereby, in dependency of the material composition (chemical structure), these sensors are sensitive in different wavelength ranges and might require a strong cooling to achieve a proper SNR ratio (sometimes down to cryogenic temperatures using liquid nitrogen or a small Stirling cycle refrigerator unit).
In contrast to silicium-only based CCD and CMOS sensors, an InGaAs sensor is made of different materials. Combining these materials is a relative complex and time consuming technology, as many manufacturing steps are needed. Additionally, theproduction yield is relatively low. This is mainly caused by difficulties that may occur when connecting the CMOS read-out circuit with the photosensitive part of the sensor. All this makes these sensors types quite expensive.
Two other points may be of interest: Currently, it is impossible to combine the ROIC (read-out circuit) with the photosensitive area with 100% accuracy. Therefore, these sensors have a much higher percentage of defective pixels than CCD or CMOS sensors, which makes a proper image correction in the camera inevitable. Moreover, the thickness of the Indium Phosphide (InP) layer determines the spectral sensitivity range of the sensor. The thinner it is, the more light with higher energy can pass through.
Moisture Detection
Water absorbs strongly at wavelengths of 1450 nm and 1900 nm. By using a corresponding filter or lighting, this feature can be used for various inspection tasks:
Verification of coatings or dryness uniformity in bulk material
Fill level detection through non-transparent containers
Detection of damaged or bruised fruit
Gauging relative water content in plants
Items with higher water distribution will appear darker than drier ones.
The technique described is usable in many industries like:
Food & beverage, agriculture
Mining
Woodworking and lumber
Textile and clothing
Automotive
Short-wave infrared cameras enable various types of new appli- cations or enhance current machine vision systems by imaging beyond the visible spectrum.
As an example, SWIR cameras are often able to "see" through surfaces that are non-transparent to the human eye. This feature helps to visualize underlying features such as fill levels, hidden moisture, or tamper-proof security codes.
In contrast to MWIR cameras, SWIR cameras do not always require sensor cooling. In addition, no special lenses are needed as wavelengths between 900 nm to 2700 nm can pass through glass. All this helps to keep the overall system costs at a moderate level.
Additionally the usage, the use of filters, wavelength disper- sive optics, or monochromatic light sources are convenient to capture a distinct and a measurable contrast of the inspected object.
Defense applications for SWIR InGaAs cameras
Key performance indicators:
SWIR InGaAs imagers are sensitive to nightglow (1 to 1.6 µm)
SWIR InGaAs cameras can be uncooled, small, lightweight and low-power
Covert and eye-safe lasers, e. g., at 1550 nm, can be used to illuminate targets
Unlike LWIR and MWIR imagers, SWIR imagers see reflected light. SWIR InGaAs cameras offer unique capabilities, complementary to LWIR and MWIR cameras.
Detection of laser designators
Many applications exist for lasers on the modern battlefield: range-finding lasers are used to detect the range of an object whereas target designator lasers are used for attack.
The most common military lasers operate around 850 nm, 1060 nm, or 1550 nm. The first two types are visible to night vision goggles; the third one, 1550 nm, is therefore considered covert. SWIR InGaAs cameras are able to see all three at the same time.
Nightvision and target recognition
Thermal imaging cameras, such as LWIR uncooled microbolometer cameras, have excellent detection abilities at night. SWIR InGaAs cameras however, are a good complement to thermal imaging cameras.
While thermal imaging can easily detect the presence of a warm objects, e. g., cars, trucks, people etc.., in a cooler environment, a SWIR camera can be used to identify and recognize those objects.
SWIR nightvision is based on reflection of infrared rays from atmospheric glow or nightglow rather than on thermal radiation. Therefore, SWIR images are close representations of what is seen in the visible spectrum. Compared to thermal imagers, SWIR InGaAs cameras also have a better dynamic range.
Thermal imagers are another class of camera with good detection abilities. Sensors Unlimited often recommends that such imagers are a good compliment to SWIR. While thermal imaging can detect the presence of a warm object against a cool background, a SWIR camera can actually identify what that object is. That’s because thermal imagers do not provide the resolution and dynamic range of imaging possible with an InGaAs SWIR focal plane array. In the military world, the serious problem of determining whether a threatening vehicle is a civilian truck or a military tank is crucial. SWIR can help with this friend-or-foe determination.
CMOS and CCD imagers are excellent devices that continue to evolve to meet military needs. But such sensors are typically just daylight sensors. On the other hand, a single SWIR camera can be used for both day and night imaging.
Obviously, a VISNIR InGaAs camera benefits from its ability to see more wavelengths when there is some visible light present, for example from street lights or urban glow. Additionally, by using SWIR illumination for example 1550 nm LEDs or lasers, a scene can be covertly illuminated, i. e., viewing is only possible with a SWIR camera. Moreover, SWIR lasers are eye-safe, i. e., they can be used to safely illuminate targets and humans.
Laser gated imaging
Laser gated imaging allows for imaging at long distances while reducing the effect of obscurants in the atmosphere. In laser gated imaging, a pulsed laser is used to illuminate the scene while the reflected light is detected by a camera with a short exposure or gating time. The exposure is delayed so imaging occurs at a particular distance, thus the image is only from the reflection of objects at that distance. When using a SWIR InGaAs camera, covert and eye-safe pulsed lasers can be used.
Situational awareness – gunshot detection
Acoustic sensors that "listen" to the shockwave of a bullet are not the only solution for gunshot
detection. Gunshot signature can be identified, located and processed even faster using high-speed SWIR InGaAs cameras, either at night or during daytime. The combustion gases and hot debris projected from the gun upon firing are detectable.
Seeing through haze, smoke and fog
Compared to visible cameras, SWIR InGaAs cameras offer superior performance in imaging through dust, fog, haze or smoke In case of fire, the location of the flames can easily be found.
Spectroscopic Analysis
Unique molecular absorbance of light is not only evident in the MWIR spectrum, but also at shorter wavelengths in the SWIR, NIR, and visible spectrum. Hence, the spectral response can be collected either by acquiring the reflected or transmitted light.
Spectroscopy is non-destructive and requires no sample prepa- ration in general. Therefore, many material attributes can be measured rapidly in-line for qualitative as well as quantitative parameters.
Applications are:
Structural clarification of unknown substances
Categorization of purity of substances by quantitative definition
Probing of bulk material with minimum sample preparation (Chemometrics)
Determination of chemical classification numbers
Quality analysis of agricultural products
Plastics sorting
Semiconductor/Solar Cell Inspection
In the wafer and solar cell production, electroluminescence (light emission as a response to electric current) is used espe- cially in the final production step of quality inspection to detect micro-cracks and printing problems. Whereas, photolumines- cence (light emission as a response to light) can be applied throughout the entire manufacturing process. SWIR cameras are most qualified for these tasks because the light emitted by silicon has a peak at 1150 nm. Moreover, the quantum efficiency of InGaAs sensors is much higher towards NIR-enhanced cooled or uncooled CCD and CMOS cameras that are sensitive up to ~1000 nm.
Additionally, at wavelengths below 1150 nm silicon is non-trans- parent. Thus, SWIR cameras are perfect for analyzing metall- ization and electrical contact errors on the backside of wafers.
Further Applications
Metal and glass industry: Thermal imaging of hot objects (ranging from of 250 °C to 800 °C)
Medical, science, and biology: Laser gauging
Print industry: Banknotes inspection
Art inspection
Vision enhancement
Near/Short wave Infrared Sensors for Optical Coherence Tomography (OCT) High Resolution Imaging in Tissue
Optical Coherence Tomography (OCT), a low-coherence interferometry technique, is well established as a non-invasive clinical tool for high resolution ophthalmic imaging of the retina. By using the 1.05 µm central wavelength, instrumentation companies are now developing systems to image deeper through the retina into the blood vessel layer (called the choroid) to diagnose eye diseases and monitor treatment. Developing clinical applications are in Endoscopy, both in the esophagus or in the arteries, and dentistry.
Image Through Glass
Finally, one major benefit of SWIR imaging that is unmatched by other technologies is the ability to image through glass. Meaning, cameras can use conventional, cost-effective visible camera lenses for all but the most demanding applications. For SWIR cameras, special expensive lensing or environmentally hardened housings are mostly unnecessary – making them available for a wide variety of applications and industries. This ability also allows for the shortwave IR camera to be mounted inside a protective window, providing extra flexibilty when positioning the camera system on a potential platform.
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