The design of efficient solar cells, which harness energy to generate electricity or produce hydrogen by splitting water, has received much attention around the world. Another way to harness the abundant and free solar energy is to use it as a pumping source for lasers. High-power lasers are intended for several applications, including deep-space communication, atmospheric sensing, high-temperature material processing, and hydrogen production. But, they are often expensive and suffer from performance degradation due to the effects of thermal stress.
In a recent study published in the SPIE Journal of Photonics for Energy, Algerian and Portuguese researchers report a new solar-powered laser design that successfully solves these problems. This laser has improved laser conversion efficiency compared to those pumped with conventional sources (such as flash lamps and LEDs).
“The approach we took in this study allowed us to develop a powerful solar-powered laser operating in TEM00 mode, the fundamental or lowest-order mode,” says Associate Professor Dawei Liang of Universidade Nova from Lisboa in Portugal, the corresponding author of the study. “Each of these modes (our laser supports several fundamental modes) can be precisely controlled with minimal heat input into the pump cavity. This allows us to tailor the energy applied to the specific needs of an application,” he adds.
Researchers performed numerical simulations to optimize the design parameters of a solar Nd:YAG laser beam in TEM00 mode. Additionally, they used four laser bars inside four 2V-shaped pump cavities and pumped them with sunlight using four large off-axis parabolic mirrors with a total collection area of 10 m2.
“Our design’s laser head also includes four secondary aspherical fused silica concentrators and four rectangular fused silica light guides. This ensures an even distribution of the pump power drawn into each rod and helps prevent heat damage. resulting from thermal lensing and heat stresses that occur in conventional single-rod solar lasers,” says Liang.
This resulted in improved performance of the solar laser. Numerical calculations estimated a total laser power of 155.29 watts in TEM00 mode. This resulted in a two-fold improvement in collection efficiency and a 1.24-fold improvement in conversion efficiency over those recorded for earlier designs with a similar setup.
One of the main potential applications for this design is for solar power generation in space. It involves collecting solar energy in outer space, converting it into a laser beam, and sending it to Earth where it can be used to generate electricity using solar cells. Since this process is not influenced by the Earth’s atmosphere, it is more stable and requires smaller transmitting and receiving equipment than needed for microwave power transmission.
Liang notes that while a photovoltaic-powered diode-pumped laser still has higher solar-to-laser conversion efficiency than a solar-powered laser, it is much less suitable for long-term space applications. This is because a diode pumped laser has a limited lifetime of the diode pump source and a more complex laser system. A solar-powered laser enjoys much greater system simplicity and benefits from an almost eternal, free pumping source.
Overall, this study illuminates a way to take solar-powered lasers to new heights, with a clear blueprint for high-efficiency, space-ready solar-powered lasers.
Research report:Efficient solar laser in TEM00 mode using four Nd:YAG rods / four off-axis parabolic mirrors pumping approach
SPIE – International Society for Optics and Photonics
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