The conversion of sunlight into laser light by direct solar pumping is of increasing importance because broadband sunlight can be converted into laser light, which is an extraordinarily useful source of narrowband, collimated, either continuous-wave or rapidly pulsed, radiation with the possibility of obtaining extremely high brightness and intensity. Entirely avoiding arc lamps or semiconductor laser arrays along with their associated electrical power generation and power conditioning equipment, direct solar laser pumping might exhibit very promising potential in partially replacing electrically-powered lasers in the future, enabling the most reliable, especially space borne, renewable laser emissions over a multitude of years.
Simplicity, low cost, and easy laser power scalability are the most distinguishing features of solar-pumped lasers. Among the potential space applications of solar lasers are remote sensing from space, wireless space power laser beaming, asteroid deflection, nudge space debris off course, fuel-free photonic thruster etc. Back to Earth, solar laser has also large potentials for many terrestrial applications such as ultra-high temperature materials processing and renewable reduction of Magnesium from Magnesium Oxide. All the above-mentioned applications can only be feasible with significant progress in solar laser efficiencies.
High beam quality, most preferably, TEM00-mode solar laser emission has become a vital issue since it produces the smallest beam divergence, the highest power density and, hence, the highest brightness. All research efforts are, therefore, concentrated on achieving the most efficient solar-powered lasers with the highest efficiency, most preferably with high beam quality.
Previous record-high solar laser was pumped through a large Fresnel lens mounted on a solar tracker. Its solar laser head moved together with whole solar tracking structure, an optical fibre was hence necessary for the transportation of solar laser radiation to a fixed target position. This, in turn, affected negatively the efficiency of whole solar laser system due to optical fibre transmission loss. Therefore, the advantage of having a stationary laser head at the focus of a primary concentrator becomes much more pronounced for many applications such as laser material processing where a vacuum chamber can be easily installed nearby.
We report here significant progresses in both multimode and TEM00–mode solar-pumped laser collection efficiencies by end-side-pumping a 4.0 mm diameter 35.0 mm length Nd: YAG
single-crystal rod with a heliostat-parabolic mirror solar energy concentration system.
An aspheric fused silica lens was used to couple the concentrated solar radiations from the focal zone of a 1.4 m effective diameter parabolic mirror into the laser rod within a conical pumping cavity. 37.2 W continuous-wave multimode 1064nm solar laser power was measured, corresponding to 31.5 W/m2 multimode collection efficiency and 8.9% slope efficiency, corresponding to the highest solar laser efficiency to date. By adopting an asymmetric large-mode laser resonant cavity, 9.3 W
continuous-wave TEM00-mode (M2 ≤ 1.2) 1064nm solar laser power was also measured, resulting in 7.9 W/m2 fundamental mode laser collection efficiency, being 2.6 times higher than the previous record by a Fresnel lens and nearly 2.0 times higher than the previous record by a parabolic mirror.
Stable emission of the most efficient solar laser radiation from a stationary solar laboratory, both in multimode and fundamental mode regimes, could constitute one step further for many interesting applications by solar-powered lasers.
Citation: Dawei Liang1 , Joana Almeida1, Cláudia R. Vistas1, Emmanuel Guillot2 . Solar-pumped Nd:YAG laser with 31.5 W/m2 multimode and 7.9 W/m2 TEM00-mode collection efficiencies. Solar Energy Materials and Solar Cells, Volume 159, January 2017, Pages 435–439.Show Affiliations
- CEFITEC, Departamento de Física, FCT, Universidade NOVA de Lisboa, 2829-516, Campus de aparica, Portugal
- PROMES-CNRS, 7 rue du Four Solaire, 66120 Font Romeu, Odeillo, France