New laser technology which can measure changes in light one millionth of the size of an atom could revolutionise their use in quantum technologies and healthcare.

A team from the University of St Andrews and M Squared Lasers has used the principle of random scattering of light to create a new class of laser wavemeter.

Dr Graham Bruce from the School of Physical and Astronomy explained: “If you take a laser pointer, and shine it through Sellotape or on a rough surface like a painted wall, on closer inspection of the illuminated surface you’ll see that the spot itself looks grainy or speckled, with bright and dark patches.

“This so-called ‘speckle pattern’ is a result of interference between the various parts of the beam which are reflected differently by the rough surface.

“This speckle pattern might seem of little use but in fact the pattern is rich in information about the illuminating laser.

“The pattern produced by the laser through any such scattering medium is in fact very sensitive to a change in the laser’s parameters and this is what we’ve made use of.”

Wavemeter breakthrough

University of St Andrews

Conventional wavemeters analyse changes in the interference pattern produced by delicate assemblies of high-precision optical components.

The cheapest instruments cost hundreds or thousands of pounds, and most in everyday research use cost tens of thousands.

In contrast, the team realised a robust and low-cost device which surpasses the resolution of all commercially-available wavemeters.

They did this by shining laser light inside a 5 cm diameter sphere which had been painted white, and recording images of the light which escapes through a small hole.

The pattern formed by the light is incredibly sensitive to the wavelength of the laser.

The breakthrough, which has been published in the prestigious journal Nature Communications, opens a new route for ultra-high precision measurement of laser wavelength, realising a precision of close to one part in three billion, which is around 10 to 100 times better than current commercial devices.

This precision allowed the team to measure tiny changes in wavelength below 1 femtometre: equivalent to just one millionth of the diameter of a single atom.

They also showed that this sensitive measurement could be used to actively stabilise the wavelength of the laser.

In future, the team hope to demonstrate the use of such approaches for quantum technology applications in space and on Earth, as well as to measure light scattering for biomedical studies in a new, inexpensive way.

Professor Kishan Dholakia from the School of Physical and Astronomy said: “This is an exciting team effort for what we believe is a major breakthrough in the field. It is a testament to strong UK industry–university co-operation and links to future commercial opportunities with quantum technologies and those in healthcare.”