New lasers will be able to provide more precise 3D models, which could be used in facial recognition, for example. | Keystone/AP Photo/Marcio Jose Sanchez

In the laboratory, as in the cinema, laser beams appear to be unbroken streams of coloured light. In reality, however, they are composed of a series of impulses emitted in such rapid succession that we are unable to distinguish the intervals. Ultrafast lasers take this principle to the extreme, emitting pulses every billionth of a second. This means they can also be used to measure time intervals, and thereby distances, with great accuracy. A team from ETH Zurich headed by Ursula Keller has pushed the limits of these devices even further – both in terms of size and energy consumption – by optimising the amplification stage. Their laser generates pulses lasting 0.3 billionths of a billionth of a second.

All lasers exploit the same phenomenon: when an atom at an excited energy level receives a photon, it emits a second photon of the same frequency and phase. This creates a chain reaction that produces a photon flux: this is the laser beam. In their amplifier, Keller and her team in Zurich have used a nanostructured semiconductor for the self-generation of quantum dots. It traps the excited electrons, and thereby amplifies photon emission. “With a density of one trillion quantum dots per square millimetre, this material lends itself to the design of high-performance, compact and energy-efficient femtolasers”, says Keller.

Ultrafast lasers have recently begun to appear in consumer devices. In the latest iPhone, they are used for facial recognition: the phone emits a laser beam cloud and analyses the photons reflected by the user’s face and then creates a 3D model. The low power is, however, a limitation, restricting it to use with nearby objects. This is because the number of photons being reflected to the sensor decreases with distance. “Our technology would allow a larger physical environment to be measured in 3D with micrometric accuracy”, she says.