Lasers and measurement

Measurement and analysis have been transformed by the laser. Surveyors use lasers to mark out roads and construction sites, the military use them to determine the position of targets and even NASA has utilised lasers to measure the distance of the moon from the earth

Key facts

Measuring the distance to the Moon

Thanks to special mirrors left behind by Apollo astronauts, the distance from the Earth to the Moon is known with a precision of millimetres!

Laser light fired from the Earth is reflected back by these mirrors (lunar retro-reflectors) and by accurately recording the time the light takes to travel, the distance to the Moon can be determined.

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Do lasers hold the key to unlocking the secrets of the Universe?

The very fabric of space and time continually undergoes subtle ‘ripples’ that carry messages of astronomical events. These include the mergers of massive black holes, neutron stars and even the aftermath of the Big Bang.

The ‘ripples’, or gravitational waves, were predicted almost a century ago by Einstein’s General Theory of Relativity. Detecting and studying them will provide an entirely new way to observe and understand the Universe.

The Laser Interferometer Space Antenna (LISA) experiment aims to do just that. An ESA/NASA joint venture, LISA will consist of three separate, identical spacecraft flying in an equilateral triangle arrangement, with ‘laser arms’ about 5 million kilometres long.

Tiny changes in the relative length of these arms caused by gravity waves will be measured by precisely monitoring the separation between each spacecraft. From studying the shape and timing of these waves, the LISA research team will be able to infer information about the astronomical systems that emitted them, such as their nature and evolution.

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Using lasers to measure gravity

As well as being able to generate extremely high temperatures, lasers can also be used to cool down atoms to temperatures close to absolute zero (-273°C).

When laser cooling is combined with another technique called magneto-optical trapping, it is possible to produce samples of trapped, slow moving, neutral atoms that are close to absolute zero.

Following research carried out by US physicists, scientists at STFC are now working on a device that incorporates a magneto-optical trap into a system capable of measuring gravity to high accuracy. By ‘dropping’ these cold atoms down a vertical vacuum tube, precise gravitational measurements can be made.

Such devices have potential applications in geophysics and in oil exploration.

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Lasers in archaeometry and art

Non-invasive laser diagnostic techniques have been used to identify, date and analyse ancient artefacts, rocks and dinosaur fossils.

Archaeologists have also applied laser-scanning techniques to sites such as Stonehenge (Wiltshire, UK), leading to the discovery of lost ancient art.

In addition, lasers have been employed to scan and survey ancient sites, allowing archaeologists to generate 3D images and visualise their excavations during its various stages. Lasers are also being increasingly used in the examination and conservation of paintings and artwork.

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Science and Technology Facilities Council Switchboard: 01793 442000