Soap bubbles are mostly known for their attention-grabbing effect on small children, but Slovenian researchers from the Jožef Stefan Institute (IJS) have now shown that these also have the property of generating colour-tunable laser light.

So far it has been known that the allure of soap bubbles comes in large part from their interaction with light - as bubbles dance through the air, they sparkle like glitter, shifting hues as they move.

This phenomenon, known as iridescence, comes from the interference of light waves within a bubble's soapy shell.

Research has also shown that laser light can propagate within a bubble's shell, and this led Matjaž Humar and Zala Korenjak of the country's prime scientific institute to wonder whether a bubble could be used to create laser light.

They indeed demonstrated that a dye dissolved in the soap solution that creates a bubble can amplify light circulating in the spherical shell and produce laser light, the IJS said.

The researchers from the institute's department for condensed matter physics have thus created a laser that could act as a sensitive sensor for measuring atmospheric pressure or detecting changes in the electric field.

The research, published in the scientific journal Physical Review X, has shown that while the idea works, soap bubble lasers are not practical, as water constantly evaporates from the bubbles, changing their shape and size.

For a more stable laser, Humar and Korenjak turned to smectic liquid-crystal bubbles, whose shells had identical thickness and were exceptionally stable.

The bubbles were attached to the end of a capillary or were freely floating in a container filled with carbon dioxide, and the spectrum of laser light emitted by the bubbles consisted of hundreds of evenly distributed sharp points.

Based on the spectrum of the emitted laser light and its change over time, the researchers were able to detect changes in the size of a bubble that measure only ten nanometres, or 10,000 times less than the thickness of a human hair.

This remarkable precision enabled the use of smectic liquid-crystal bubbles as one of the most sensitive electric field and pressure sensors developed so far, the IJS said.

The bubble as a unique system could also be used as an extremely sensitive microphone, a magnetic field sensor or as a platform for studying interesting processes in thin layers, it added.