Lasers zoom in on 3D precision

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A team of Scotland-based physicists has developed laser technology to the extent that high-resolution, 3D images, precise to the millimetre, can be taken from up to a kilometre away.

The research team from Heriot-Watt University revealed its findings in today’s Optical Society of America’s (OSA) open-access journal Optics Express.

To obtain 3D information, such as the distance to a far-away object, scientists can bounce a laser beam off the object and measure how long it takes the light to travel back to a detector. The technique, called time-of-flight (ToF), is already used in machine vision, navigation systems for autonomous vehicles and other applications, but many current ToF systems have a relatively short range and struggle to image certain objects.

Led by Professor Gerald Buller, the research team at Heriot-Watt University has developed a system that captures laser pulses from ‘uncooperative’ objects that do not easily reflect laser pulses, such as fabric, making it useful in a wide variety of field situations.

The system works by sweeping a low-power infrared laser beam rapidly over an object. It then records, pixel-by-pixel, the round-trip flight time of the photons in the beam as they bounce off the object and arrive back at the source. The system can resolve depth on the millimetre scale over long distances using a detector that can ‘count’ individual photons.

The primary use of the system is likely to be scanning static, human-made objects, such as vehicles. With some modifications to the image-processing software, it could also determine their speed and direction.

Dr Aongus McCarthy, Research Fellow at Heriot-Watt University, said: 'Our approach gives a low-power route to the depth imaging of ordinary, small targets at very long range.

'While it is possible that other depth-ranging techniques will match or out-perform some characteristics of these measurements, this single-photon counting approach gives a unique trade-off between depth resolution, range, data-acquisition time and laser-power levels.'