A laser that uses glowing green proteins found in jellyfish has been unveiled by researchers in the UK and Germany.
The new device, which falls into the polariton family of lasers, uses less energy than conventional lasers. The work was published in Science Advances.
The word laser was originally an acronym for “light amplification by stimulated emission of radiation” as the most familiar type of lasers, such as those in DVD players or laser pointers, generate light using – you guessed it – stimulated emission of radiation.
They do this by “pumping” atoms with energy which propels electrons into a higher-energy, excited state.
When the electrons relax into their lower energy orbit, they spit out a photon – the wavelength of which depends on the state of the excited electron’s energy.
A pair of mirrors reflect the photons back and forth through the atoms. That can trigger even more electrons to excite and relax, releasing more photons of the same wavelength.
But for the past couple of decades researchers have been experimenting with a different type of laser, one that uses quantum phenomena called polaritons.
Polaritons are quasiparticles – part matter and part light – inside minuscule cavities inside a solid material that can conduct electricity under some circumstances (called a semiconductor).
As polaritons decay, they emit photons as laser light.
These devices use less energy than many conventional lasers, but there’s a catch – the early ones needed to be very cold to work. We’re talking only 10 °C above absolute zero, or around -263 °C.
green fluorescent protein looks like a barrel surrounding a light-emitting molecule.
At this temperature, the polaritons can easily fall into the same energy state and synchronise their light emission. This synchronicity (or coherence) is what makes laser light different from regular light. But at higher temperatures they start to get in each other’s way and don’t produce photons.
In 2014, a team at the University of Michigan unveiled a polariton laser that could work at room temperature. They squashed a thin strip of the semiconductor gallium nitride between stacks of metal oxide mirrors. When they passed voltage through the semiconductor’s microcavities, polaritons were generated and laser light produced.
But this year, doubts arose over some of those claims.
Now, physicists at the University of Würzburg and the University of St Andrews in the UK say a naturally occurring material can do the trick – a protein originally found in jellyfish that fluoresces under certain wavelengths of light.
The protein, called green fluorescent protein or GFP, looks like a barrel surrounding a light-emitting molecule. It’s widely used in biomedical research. The gene that produces GFP can be inserted into living species, such as bacteria, fish and even cats.
In this case, the team enlisted the help of genetically modified E. coli bacteria to manufacture a 500-nanometre-thick film of GFP, which they sandwiched between two mirrors.
And when they shone blue light on the film, it radiated laser light.
The key to GFP is its natural structure. The cylindrical shells keep light-emitting molecules away from each other, even when at room temperature.
And because the new laser doesn’t need a blast of energy to get started, it uses less power.
So the next time you watch a jellyfish lazily drift with an ocean current, think of its proteins – and that one day, they may power the laser with which you entertain your glowing kitten.
Belinda Smith is a science and technology journalist in Melbourne, Australia.
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