Drones in the sky with diamonds
Electric drones are severely restricted by their battery life. Using lab-grown diamonds to recharge them in flight will enable them to stay in the air.
Drones have a bright future ahead of them. Of the various types of aircraft, multicopters — helicopters with multiple rotors — offer huge potential due to the manoeuvrability of their numerous propellers. These unmanned aerial vehicles can fly in all directions and at any time. These features mean that the devices are ideally designed for use in disaster areas, buildings, farmland, offshore facilities such as oil rigs and wind farms, and as delivery vehicles.
The only hurdle to their widespread use is flight time. This type of drone runs exclusively on a battery-powered electrical system. Their current maximum flight time in good weather conditions is only about 20 minutes. That significantly reduces the uses to which they may be put.
Using light as an energy source
Until now, the solutions tested to extend the flight time of electric drones have been relatively inconclusive. For example, hooking drones up to an electrical cable considerably reduces manoeuvrability and range. Adding batteries does not help, as the added weight increases energy use and therefore reduces flight time. So why not use solar power? This option is currently complex, as the surface area required by solar panels is too large for drones to be able to fly. However, the idea has led to another original solution: using a laser as an energy source to power the drone continuously or to recharge its batteries while in the air.
That is achieved by equipping the drone with a photodiode — basically a solar cell that only works on a single wavelength — that converts light into electricity. A laser is then pointed at the photodiode using a remote guidance system. For the system to work, the laser beam must have three essential properties: it must be of impeccable quality — i.e. its light rays must remain as parallel as possible to avoid losing energy through divergence, it must be high-power and it must not be harmful to human health. However, no laser on the market currently offers all these qualities.
Diamonds at the laser core
The Swiss company LakeDiamond, founded on the EPFL campus, produces special lasers by drawing on the expertise gained by its 25 employees over 20 years in academic research. Since being established in 2015, the company has specialised in producing ultra-pure lab-grown diamonds for advanced non-military applications, including lasers. It is this purity that gives diamonds their thermal conductivity and transparency, two essential properties for lasers designed to power drones, or VECSELs (Vertical-External-Cavity Surface-Emitting Lasers). “VECSELs work without diamonds, but lose a lot of power,” states Nicolas Malpiece, Power Beaming Project Leader at LakeDiamond.
Incorporating diamonds into the laser’s core enables the heat emitted by the light wave to dissipate. This process significantly improves the quality and power of the beam. The devices can also be built more compactly by using diamonds. “If the light source is compact, several devices can be aligned to form a laser array, which produces power proportionate to the number of light sources,” adds Mr Malpiece. He expects a turnkey solution to be available on the market within the next two years.
The Swiss start-up not only develops lasers containing diamonds but also the system that integrates them. In terms of safety, LakeDiamond also stands out from its competitors by working in “eye-safe” wavelengths within the infra-red spectrum. Between 1,400 and 1,600nm, light is absorbed by the cornea, which protects the retina. Another application for diamond lasers is the space industry. As these wavelengths are not absorbed by the Earth’s atmosphere, lasers and diamonds can be used in space.
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