Priming the Pump: Recent Design Breakthrough Can Spur Advances in Solar-Driven Lasers

Lasers are an endless source of interest for scientists and engineers alike. This is because the advent of advanced lasers has led to the development of advanced devices and helped us in understanding the workings of the world. They also have countless practical applications, such as in optical disks, remote sensing, cutting, calibration, positioning—you name it. But, since the generation of laser beams requires energy, it is crucial to find responsible sources energy owing to the current environmental crisis. Some researchers have therefore delved into solar-driven lasers, also called “solar-pumped lasers,” which convert solar energy into laser radiation.

In spite of some progress in this field, all existing solar-pumped laser devices require large lenses or mirrors to concentrate as much sunlight as possible into a small area. In fact, the minimum threshold of solar light intensity that can generate a laser in existing devices is approximately 10,000 times that of natural sunlight. In addition to the sheer bulkiness of the telescope-like lenses needed, complex solar-tracking mechanisms are required for these devices. To make things worse, these lasers cannot use diffuse sunlight, meaning that they would not work on cloudy days at all. These serious limitations have greatly hindered the adoption of solar-pumped lasers.

Fortunately, in an effort to revolutionize this field, a team of scientists from Toyota Motors and Tokai University, Japan, led by Dr Masamori Endo, have recently published a study in Communications Physics on their latest development: a fully planar solar-pumped laser. This solar-pumped laser does not require complex light-concentrating systems and—by virtue of being fully planar and having a thickness of only a few millimeters—can be easily deployed like traditional solar cells.

So, how does this novel design work? It mainly relies on a nearly flat cylindrical chamber called “luminescent solar collector.” The inside of the chamber is highly reflective and contains a solution called “sensitizer.” A coiled kilometer-long laser fiber is submerged in the solution, and the top of the chamber is a dichroic mirror. Solar photons (or light particles), which have a wide range of frequencies, enter the chamber through the dichroic mirror and are absorbed by the sensitizer, which re-emits them with a specific frequency through photoluminescence. These photons are now reflected by the dichroic mirror and are therefore trapped within the chamber. They eventually hit the laser fiber and excite it, collectively producing the required oscillations that generate a laser beam.

This approach, which represents a complete overhaul of existing solar-pumped laser designs, was tested experimentally. Although the first results were unsatisfactory as the output power of the prototype was too low, Dr Endo and his team knew they were onto something exciting. In a subsequent study, published in the Journal of Applied Physics, they tried to improve upon their initial design by replacing their previous sensitizer with cesium lead halide perovskite nanocrystals, which they chose because of their advantageous optical properties. By tailoring the composition of the perovskites, they tuned the energy of the photons emitted via photoluminescence to match the optimal one required to excite the atoms in the laser fiber. This new prototype device yielded better results and provided relevant insight into the physics at work within the planar solar-pumped laser.

Solar-pumped lasers are especially important because they can be used to produce hydrogen, a clean type of fuel that is expected to change the world in the near future. Excited about their present results and future prospects, Dr Endo remarks, “This is a great step toward our goal, realization of a “hydrogen-society.” We continue our efforts to implement our solar-pumped laser as part of a hydrogen-generation platform. We believe that hydrogen is one of the best solutions to the increasing demand for renewable energy.

Dr Endo, a huge fan of hard science fiction, also says that a solar-pumped laser without concentrator optics sounded like a very futuristic concept when he began his research. Now that it is becoming a reality through much effort, various advanced applications are plausible. He concludes, “Direct energy transfers from space to remote areas could be a practical solution for power shortages. Of course, they can also be used as a power supply for outer space exploration.

These findings certainly generate hope that the future of solar-pumped lasers is here!


Authors: Taizo Masuda1, Mitsuhiro Iyoda2, Yuta Yasumatsu2, Stephan Dottermusch3, Ian A. Howard3,4, Bryce S. Richards3,4, Jean-Francois Bisson2,5 and Masamori Endo2

Titles of original papers:
A fully planar solar pumped laser based on a luminescent solar collector
All-inorganic cesium lead halide perovskite nanocrystals for solar-pumped laser application

Communications Physics
Journal of Applied Physics

10.1038/s42005-020-0326-2 – Communications Physics
10.1063/5.0011945 – Journal of Applied Physics

1S-Frontier Division, Toyota Motor Corporation
2Department of Physics, Tokai University
3Institute of Microstructure Technology, Karlsruhe Institute of Technology
4Light Technology Institute, Karlsruhe Institute of Technology
5Département de physique et d’astronomie, Université de Moncton

About Dr Masamori Endo from Tokai University

Dr Masamori Endo received BA and PhD degrees from Keio University, Japan, in 1988 and 1993, respectively. He joined Tokai University as a full-time lecturer in 2000 and now leads his own laboratory in the Department of Physics. His current research interests include diode-pumped alkaline lasers, optical resonators, laser processing, and solar-pumped fiber lasers. Dr Endo is a senior member of the International Society for Optical Engineering, a member of the American Institute of Aeronautics and Astronautics, the Applied Physics Society of Japan, and the Laser Society of Japan. He has 12 books, 70 academic papers, and over 200 conference proceedings to his credit.

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