off the object and measure how long it takes the light to travel back to a detector.
The technique, called time-of-flight (ToF) navigation systems for autonomous vehicles, and other applications, but many current systems have a relatively short range and struggle to image objects that do not reflect laser light.
Researchers have tackled these limitations and reported their findings in the journal Optics Express.
The research team, led by Gerald Buller, professor at Heriot-Watt University in Edinburgh, Scotland, describes a ToF imaging system that can gather high-resolution, 3-D information about objects that are typically very difficult to image, from up to a kilometre away.
The new system works by sweeping a low-power infrared laser beam rapidly over an object. It 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 ability of the new system to image objects like items of clothing that do not easily reflect laser pulses makes it useful in a wider variety of field situations, said Aongus McCarthy, the first author of the study.
"Our approach gives a low-power route to the depth imaging of ordinary, small targets at very long range," McCarthy said.
"Whilst 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," he said.
The primary use of the system is likely to be scanning static, human-made targets, such as vehicles. With some modifications to the image-processing software, it could also determine their speed and direction.
One of the key characteristics of the system is the long wavelength of laser light the researchers chose. The light has a wavelength of 1,560 nanometres, meaning it is longer, or "redder," than visible light.
This long-wavelength light travels more easily through the atmosphere, is not drowned out by sunlight, and is safe for eyes at low power.
Ultimately, McCarthy says, it could scan and image objects located as far as 10 kilometres away.