A new design for a laser that is powered by sunlight has been unveiled by researchers in Algeria and Portugal.  The solar laser, which has yet to be built in the lab, is predicted to operate at a higher efficiency than existing systems and could have numerous applications – including a space-borne system for harvesting solar energy for use on Earth.

The use of sunlight as a pumping source for producing laser light has been widely explored since the 1960s. Current technologies can be used to produce cost-effective laser systems with high power and brightness.

Numerous advances in solar lasers have been made over the past decade – but existing designs can be limited by their use of a single large laser rod. This rod is the gain material that produces laser light through the energy it acquires from the pump source. Single-rod solar systems tend to be expensive and suffer from uneven temperature distributions within the rod, which diminishes the quality of the beam it produces.

Numerical simulations

This latest work was done by Rabeh Boutaka at the Centre for the Development of Advanced Technologies in Algiers, Dawei Liang at NOVA University Lisbon and Abdelhamid Kellou at the University of Science and Technology Houari Boumediene. The trio did numerical simulations to help them design a more optimal solar laser set-up. Their proposed system would operate in the TEM₀₀ optical mode: the fundamental, lowest-order laser mode, where the intensity of light surrounding the centre of the beam follows a simple Gaussian distribution. The team’s design collects sunlight using four parabolic mirrors with a total area of 10 m².

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Once this light has been harvested, it is directed to a laser head, where it is distributed evenly between four fused-silica concentrators and light guides. Finally, the light is used to simultaneously pump four small-diameter laser rods – with the set-up ensuring that pump power is distributed evenly between the rods. As a result, the design avoids the limitations presented by thermal lensing – an unwanted effect whereby temperature irregularities in an optical material affects the paths taken by light.

Altogether, Boutaka’s team calculated that their alterations doubled the light collection efficiency of solar lasers operating in the TEM₀₀ mode, resulting in 1.24 times the sunlight-to-laser conversion efficiency of previous designs. The researchers envisage numerous potential applications for their design: including better methods for monitoring the Earth’s surface and atmosphere using satellites; along with the removal of space debris, and deep-space communications.

Perhaps the most fascinating application is the development of new forms of solar energy production. Here, Boutaka and colleagues propose that solar lasers could operate in space, where sunlight is around twice as strong as it is on Earth. Laser beams could be fired back to Earth, and collected by concentrated solar cells – in a process that is more efficient than ground-based solar energy collection.

The research is described in the Journal of Photonics for Energy.