Making the invisible visible

Since February 2017, the ESA mission NELIOTA has been monitoring the moon with a telescope to record meteorite and asteroid impacts. 58 Near-Earth Objects (NEOs) hit the surface within 813 days. Researchers at the National Observatory of Athens recorded them with two 5.5 megapixel sCMOS cameras from Oxford Instruments subsidiary Andor. They provide 30 very high resolution images per second, which have nanosecond-exact timestamps. The cameras also film on two different photometric bands, which also enables the researchers to determine the temperature of the weak flashes resulting from the impacts.

sCMOS (PDF, 8,44 MB) (scientific complementary metal-oxide-semiconductor) sensor technology provides especially high resolutions, high detective quantum efficiency, frame rates, and is impressive due to its dynamic range. NELIOTA is breaking new ground with its use in astronomy. In the past, astronomers used CCD cameras for exploration and documentation—for example, to discover earth-like planets.

By contrast, sCMOS sensor systems are well established in microscopy: sCMOS cameras from PCO, XIMEA or from Teledyne Photometrics are currently used in many different processes of bright-field and fluorescence microscopy, single molecule localization, high-throughput screening, and many more scientific imaging applications.

Quantum dot technology supplements InGaAs sensors

For imaging in the infrared spectrum (SWIR), indium gallium arsenide (InGaAs) sensors are the means of choice. But here, too, the less expensive CMOS technology is gaining ground. U.S. producer SWIR Vision Systems combines CMOS pixels with crystalline colloidal quantum dots (CQD) in its new Acuros™ cameras. The company deposits CQD semiconductor crystals directly on to the surface of silicon CMOS circuitry—which, according to SWIR Vision, creates a monolithic photodetector structure that is significantly cheaper than InGaAs sensor technology. SWIR Vision offers CQD cameras with up to 2.1 megapixels. In combination with modern GigE or USB3 interfaces, they enable frame rates of up to 380 fps (10 bit / 640x510 px) in the spectral band from 400 to 1,700 nm. According to LASER 2000, which markets the Acuros™ cameras, they are enormously popular in the market.

SWIR imaging in the wavelength range from 900 to 1,700 nm makes the invisible visible for the human eye. For instance, silicon is transparent in the range from 1,150 nm, which the semiconductor industry makes use of in the inspection of wafers, microchips, and solar panels. Colored plastic bottles and plastic films are also transparent in the SWIR spectrum—and provide a view of food that has already been packaged. And there are dozens of other applications in which SWIR imaging with cameras from manufacturers such as Raptor Photonics, ARTRAY and Emberion OY, Hamamatsu and Xenics are now commonplace. System integrators like Acal BFi, Stemmer, and Polytec provide suitable overall solutions.

Interfaces for more bandwidth

It’s not only the choice of imaging sensors that is on the increase. Increasingly higher resolutions are driving development of new data transmission standards with gigabyte bandwidths. High-speed cameras record production processes in detail and the vision of complete quality monitoring is gradually becoming reality. Camera manufacturers keep achieving new superlatives. For example, SVS-Vistek reported the “fastest 31 megapixel camera with Sony’s IMX342 sensor in the market” and has already announced a CMOS area scan camera with an incredible resolution of 151 megapixeln for extremely accurate inspections of wafers, solar panels, and displays. Fourfold CoaXpress or new 10GigE interfaces provide the necessary bandwidth. If you combine four CoaXPress interfaces each with 6.25 Gbit/s, the transfer rate adds up to 25 Gbit/s.

An alternative is transfer with the new 10 Gigabit Ethernet (10 GigE) standards, which provide less bandwidth but ensure stable data rates even over transmission routes of 100 meters. An advantage that Swiss company Photonfocus also makes use of in its new MV4 platform for industrial imaging. Optronis also provides another superlative for machine vision applications. With four CoaXPress 2.0 interfaces, its high-speed cameras in the CamPerform-Cyclone series enable data rates of 50 Gbit/s. The cameras record 2,158 images per second, each with 2 megapixel resolution. At 5 megapixels, they can still take 705 pictures per second. In Industry 4.0 processes, resolutions such as this provide full transparency even at high band speeds—and make the supposedly invisible visible.

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