Flexible membrane lasers, less than a thousandth of a millimetre thick, which work as free-standing films and can stick to different materials including banknotes and contact lenses, are reported in a study published in Nature Communications this week. The authors also show that the characteristics of the laser light can serve as a unique identifier, which could be used as a security tag.

To add lasers to the collection of functional flexible optoelectronic devices, Malte Gather and colleagues developed a method to lift organic membrane lasers off a supporting substrate, allowing their transfer to various surfaces. They also demonstrated that the devices were flexible and mechanically robust, even when attached to another object, and that their optical properties did not change over the course of several months, even when they were not stored under ideal conditions.

The authors were able to stick these ultrathin lasers onto banknotes and contact lenses, where they suggest the devices could be used as flexible and wearable security tags. This is possible because by varying the materials and adjusting the grating structures of the laser, the emission can be designed to show a specific series of sharp lines on a flat background - the ones and zeros of a digital barcode.