Ultra-fast camera

Celestial images from the Very Large Telescope array are set to be given a boost, claim the developers of OCam: the world’s fastest high-precision faint-light camera.


Celestial images from the Very Large Telescope (VLT) array are set to be given a boost, claim the developers of OCam: the world’s fastest high-precision faint-light camera.

OCam will be part of the SPHERE second-generation VLT instrument. Due to be installed in 2011, SPHERE will take images of giant exoplanets orbiting near stars.

The device works alongside adaptive optics instruments to tackle the blurring effect caused by atmospheric turbulence. This is a problem common to all large ground-based telescopes and is overcome using techniques that offer real-time corrections taken from a high-speed camera.

The new generation of telescopic equipment requires these images to be taken at a rate of more than 1,000 times a second. With significant input from Chelmsford-based e2v, OCam is claimed to be the first faint-light camera able to do this and was last year granted production approval by the European Southern Observatory (ESO). However, its five-year development has come with a number of technical challenges.

Philippe Balard, a software engineer at Laboratoire d’Astrophysique de Marseille, explained: ‘This is a camera that outputs something like 200Mbps of images, which five years ago really wasn’t something you could handle easily. The fact that the camera has eight outputs also meant it was difficult to reconstruct the mass of data.

‘The camera took us two years of extra development and many people didn’t expect it to work. The biggest challenges were on the electronics side because the chip in itself was a nightmare to drive at that speed. It really hadn’t been done before, but now we have something that can work in almost any application where you need to see the object very fast in minimal light,’ he added.

OCam solves the problem of atmospheric turbulence using a high-precision CCD220 detector developed by e2v. This sensor combines speed and sensitivity to provide the OCam with a readout noise (the imperfect electrical charges that cause blurring) that is 10 times smaller than the detectors currently used on the VLT.

Dr Paul Jorden, technical specialist at e2v, said: ‘The sensor we’ve developed has a 240 x 240 pixel format and, as well as being sensitive, runs at more than 1,000 frames per second. It’s a combination of all these performance factors brought together in one device that makes it unique and we believe this detector is a world first in terms of performance.’

‘An important part of the technology that e2v has is a so-called back-thinning of the silicon sensor, which is a technique that gives a very high spectral response. We integrated this with L3 vision technology, which is a process inside the silicon sensor that allows the charge to be multiplied. This generates a charge even when you detect a very small amount of light producing a much larger signal that makes it even more sensitive,’ he added.

Plans are now under way to develop the adaptive optics detectors required for the ESO’s planned 42m European Extremely Large Telescope (E-ELT) project.

Leading the team that built the camera, Jean-Luc Gach believes there are wider applications for the technology. ‘As well as running this on the VLT, we plan to have a technology-transfer agreement with an industry partner because there might be other applications [for instance, in the medical field] where the device will be beneficial’, he said.

Balard added: ‘Since a camera that has this capability hasn’t been invented before, you don’t really know what it’s going to be used for. We expect someone will come up with something we didn’t think of. For instance, we had some guys working on thermal engines that are very interested in the camera as it would allow them to film the combustion in an engine.’

Ellie Zolfagharifard