Challenge and Research Trends of Solar Concentrators

Primary and secondary solar concentrators are of vital importance for advanced solar energy and solar laser researches. Some of the most recent developments in primary and secondary solar concentrators were firstly presented. A novel three-dimensional elliptical-shaped Fresnel lens analytical model was put forward to maximize the solar concentration ratio of Fresnel-lens-based solar concentrators. By combining a Fresnel lens with a modified parabolic mirror, significant improvement in solar laser efficiency was numerically calculated. A fixed fiber light guide system using concave outlet concentrators was proposed. The absence of a solar tracking structure highlights this research. By shaping a luminescent solar concentrators in the form of an elliptic array, its emission losses was drastically reduced. Simple conical secondary concentrator was effective for thermal applications. New progresses in solar-pumped lasers by NOVA University of Lisbon were presented. By adopting a rectangular fused silica light guide, 40 W maximum solar laser power was emitted from a single Ce:Nd:YAG rod. An aspheric fused silica secondary concentrator and a small diameter Ce:Nd:YAG rod were essential for attaining 4.5 % record solar-to-laser power conversion efficiency. A novel solar concentrator design for the efficient production of doughnut-shaped and top-hat solar laser beams were also reported. More importantly, a novel solar concentrator approach for the emission of 5 kW-class TEM00 mode solar laser beams from one megawatt solar furnace was put forward at the end of this book, revealing promising future for solar-pumped lasers

Advances in solar-pumped laser efficiency and brightness

Advances in both solar-pumped laser efficiency and brightness are herein presented. Several solar laser prototypes with both end-side-pumping and side-pumping configurations were studied and developed to efficiently pump small diameter Nd:YAG laser rods, leading to substantial increase in solar laser collection efficiency and brightness, which have gained international recognitions. All the design parameters were optimized in ZEMAX© non-sequential ray-tracing software. LASCAD© laser cavity analysis software was then used to optimize the laser resonator parameters. Based on the numerically optimization of the solar laser system, the solar laser prototypes were designed and built in Lisbon. Solar energy collection and concentration were achieved through the PROMES-CNRS heliostat-parabolic system, NOVA Fresnel lens system, and the recently new NOVA heliostat-parabolic system. Measurements of the solar input / laser output performance, beam quality M2 factors, and laser beam profiles for both multimode and fundamental mode regime were performed and compared with that of the numerical results. 13.9 W/m2 solar laser collection efficiency was achieved in 2013, through PROMES heliostatparabolic mirror system, by end-side-pumping a 5 mm diameter, 25 mm length Nd:YAG laser rod. This result was further increased to 21.1 W/m2, in 2015, within the same solar facility. In 2016, 25 W/m2 collection efficiency was reported, by end-side-pumping a thinner laser rod through NOVA heliostat-parabolic mirror system. In addition to the enhancement of solar laser collection efficiency, the thermal performance of end-side-pumped solar laser was also substantially improved. In 2017, record solar laser collection efficiency of 31.5 W/m2 was reported by end-sidepumping a 4 mm diameter, 35 mm length Nd:YAG laser rod in PROMES-CNRS heliostatparabolic mirror system. Also, record slope efficiency of 8.9% was achieved. A substantial progress in solar laser beam brightness with Fresnel lens was reported in 2013, through the first TEM00-mode solar laser. 1.9 W solar laser brightness was registered, being 6.6 times more than the previous record. The adoption of an asymmetric laser resonator, for maximum extraction of TEM00-mode solar laser, was also essential for improving significantly the solar laser brightness. By side-pumping a 3 mm diameter, 30 mm length Nd:YAG rod with a double-stage rectangular light guide / 2D-CPC concentrator, 4.0 W solar laser brightness was reported in 2015, doubling the previous record with Fresnel lens. TEM00-mode solar laser collection efficiency of 4.0 W/m2 was obtained by side-pumping a Nd:YAG grooved rod in 2016. Most recently, by endside-pumping a 4 mm diameter, 35 mm length, Nd:YAG rod, the TEM00 mode solar laser collection efficiency was almost doubled, reaching 7.9 W/m2. Record-high solar laser brightness of 6.5 W was also achieved. Advances in solar laser beam stability were also achieved by developing sculptured twisted light guides for efficient uniform redistribution of pump light into a thin and long laser rod. In addition to this, we were also able to demonstrate the first emission of doughnut shaped solar laser beam, which may widen the applications areas of solar-pumped lasers. The research efforts performed during this work for enhancing both solar laser efficiency and beam brightness are explained. Experimental results are discussed and future suggestions are proposed

40 W Continuous Wave Ce:Nd:YAG Solar Laser through a Fused Silica Light Guide

Funding Information: Funding: This research was financially supported by Science and Technology Foundation of Portuguese Ministry of Science, Technology and Higher Education (FCT-MCTES) in the framework of the strategic project UIDB/00068/2020 and the exploratory research project EXPL/FIS-OTI/0332/2021. The solar laser research was also supported by the Solar Facilities for European Research Area–Third Phase (SFERA III), Grant Agreement No. 823802. Funding Information: Acknowledgments: The authors express their gratitude for the FCT-MCTES fellowship grants CEECIND/03081/2017, PD/BD/142827/2018, PD/BD/128267/2016, 2021.06172.BD, SFRH/BD/ 145322/2019 and SFRH/BPD/125116/2016. Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.The solar laser power scaling potential of a side-pumped Ce:Nd:YAG solar laser through a rectangular fused silica light guide was investigated by using a 2 m diameter parabolic concentrator. The laser head was formed by the light guide and a V-shaped pump cavity to efficiently couple and redistribute the concentrated solar radiation from the parabolic mirror to a 4 mm diameter, 35 mm length Ce(0.1 at.%):Nd(1.1 at.%):YAG laser rod. The rectangular light guide ensured a homogeneous distribution of the solar radiation along the laser rod, allowing it to withstand highly concentrated solar energy. With the full collection area of the parabolic mirror, the maximum continuous wave (cw) solar laser power of 40 W was measured. This, to the best of our knowledge, corresponds to the highest cw laser power obtained from a Ce:Nd:YAG medium pumped by solar radiation, representing an enhancement of two times over that of the previous side-pumped Ce:Nd:YAG solar laser and 1.19 times over the highest Cr:Nd:YAG solar laser power with a rectangular light-guide. This research proved that, with an appropriate pumping configuration, the Ce:Nd:YAG medium is very promising for scaling solar laser output power to a higher level.publishersversionpublishe

Solar Concentrators and Solar-pumped Lasers

Innovative substitutions for Fresnel lenses concentrators by Elliptical shaped Fresnel lens (ESFL) and parabolic concentrators by ring array concentrator (RAC) models are presented, as well as, advances of solar-pumped lasers of Ce:Nd:YAG operation during a clean and clouded weather. The design of the ESFL and RAC were modelled into Zemax® non-sequential ray-tracing soft-ware from well-defined mathematical equations. Most of the key parameters were analysed and the resulting outputs were compared and documented in publications. The design parameters for solar-pumped lasers were optimized using Zemax®, and then the LAS-CAD™ laser cavity system software was used to further optimize the laser resonator parameters. A solar laser prototype was built with an active medium of Ce:Nd:YAG and tested using a heliostat-parabolic mirror system at both NOVA University of Lisbon and Procédés, Matériaux et Énergie Solaire - Centre National de la Recherche Scientifique (PROMES-CNRS) in Odeillo-Font Romeu, France. The ESFL offers a 4.58 W/mm2 increase in solar flux concentration compared to a Fresnel lens, which only achieves 2.66 W/mm2 at the same size and focal distance. A 3.14 m2 RAC with a focal length of 300 mm can capture over 18 W/m2. The first recorded Ce:Nd:YAG solar laser operating with a small collection area of 0.293 m2 at the NOVA facility, produced a multimode output power of 11.2 W, resulting in a solar-to-laser power conversion efficiency of 3.37%, with a minimum threshold pump power of 66 W. The MSSF parabolic mirror from PROMES-CNRS achieved a lower threshold pump power of 32.4 W using a smaller col-lection area of 0.075 m2, and during cloudy weather, a threshold pump power was further reduced to 29.2 W. Furthermore, cloud interference improved the solar-to-laser conversion efficiency to 6.32%, nearly tripling the 2.32% efficiency on a clear sky, while the solar laser conversion efficiency of 21.47 W/m2 was nearly twice the value of 12.62 W/m2 on a clear sky. The research efforts performed during this work are explained. Experimental results are dis-cussed, and future suggestions are proposed.Inovações para substituições de concentradores de lentes de Fresnel por lentes de Fresnel elípticas (ESFL) e concentradores parabólicos por modelos de concentradores de matriz de anéis (RAC) são apresentados, bem como avanços de lasers solares de Ce:Nd:YAG operando no limiar mais baixo e durante o clima nublado. O projeto do ESFL e do RAC foi modelado incorporando as equações recém-deduzidas no software de rastreamento de raios não sequencial Zemax®. A maioria dos principais parâ-metros foi analisada e as saídas resultantes foram comparadas e documentadas em publicações. Em relação aos lasers solares bombeados, todos os parâmetros de projeto foram otimizados e adaptados no Zemax® e o software de sistema de cavidade a laser LASCAD™ foi usado para otimizar os parâmetros do ressonador a laser. O protótipo de laser solar com o meio ativo de Ce:Nd:YAG foi construído e testado na instalação helióstato-parabólica na Universidade Nova de Lisboa e no forno solar de tamanho médio (MSSF) no Procédés, Matériaux et Énergie Solaire - Centre National de la Recherche Scientifique (PROMES-CNRS) em Odeillo-Font Romeu, França. O ESFL oferece um aumento de 4,58 W/mm2 na concentração de fluxo solar em comparação com uma lente de Fresnel, que alcança apenas 2,66 W/mm2 no mesmo tamanho e distância focal. Um RAC de 3,14 m2 com uma distância focal de 300 mm pode capturar mais de 18 W/m2. O primeiro laser solar Ce:Nd:YAG registrado, operando com uma pequena área de coleta de 0,293 m2 na instalação da NOVA, produziu uma potência de saída multimodo de 11,2 W, resultando em uma eficiência de con-versão de energia solar para laser de 3,37%, com uma potência mínima de bombeamento de 66 W. O espelho parabólico MSSF do PROMES-CNRS alcançou uma potência de bombeamento de limiar mais baixa de 32,4 W usando uma área de coleta de 0,075 m2 e, durante o tempo nublado, uma potência de bombeamento de limiar de 29,2 W foi registada. Além disso, a interferência das nuvens melhorou a eficiência de conversão de energia solar para laser em 6,32%, quase triplicando a eficiência de 2,32% em um céu claro, enquanto a eficiência de conversão de energia do laser solar de 21,47 W/m2 foi quase o dobro do valor de 12,62 W/m2 em um céu claro

Uniform and Non-Uniform Pumping Effect on Ce:Nd:YAG Side-Pumped Solar Laser Output Performance

Funding: This research was funded by Science and Technology Foundation of Portuguese Ministry of Science, Technology and Higher Education and the exploratory research project EXPL/FIS-OTI/0332/2021. This research was also funded by the Solar Facilities for European Research Area—Third Phase (SFERA III), Grant Agreement No. 823802. Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.The Ce:Nd:YAG is a recent active medium in solar-pumped lasers with great potential. This study focuses on the influence of two secondary concentrators: a fused silica aspherical lens and a rectangular fused silica light guide; and consequent pump light distribution on the output performance of a Ce:Nd:YAG side-pumped solar laser. The solar laser head with the aspherical lens concentrated the incident pump light on the central region of the rod, producing the highest continuous-wave 1064 nm solar laser power of 19.6 W from the Ce:Nd:YAG medium. However, the non-uniformity of the absorbed pump profile produced by the aspherical lens led to the rod fracture because of the high thermal load, limiting the maximum laser power. Nevertheless, the solar laser head with the light guide uniformly spread the pump light along the laser rod, minimizing the thermal load issues and producing a maximum laser power of 17.4 W. Despite the slight decrease in laser power, the use of the light guide avoided the laser rod fracture, demonstrating its potential to scale to higher laser power. Therefore, the pumping distribution on the rod may play a fundamental role for Ce:Nd:YAG solar laser systems design.publishersversionpublishe

Solar-pumped laser technology

In this dissertation are reported technological advancements in solar-pumped lasers and solar energy collection and concentration systems. New insights to improve the overall efficiency and the tracking error stability of solar lasers are presented, demonstrating new possibilities towards a sustainable energy generation and a low carbon industry as a solution for new segments of technology innovation. Significant progresses in solar laser efficiency and tracking error stability were obtained with numerical analysis. ZEMAX© non-sequential ray-tracing and LASCAD© resonant cavity analysis were used to optimize the optical designs and the laser cavity parameters. 38.2 W/m2 multimode solar laser in end-side-pumping configuration was achieved by using a ring-array concentrator (RAC). Dual-rod side-pumping scheme increased the multimode collection efficiency and the solar-to-laser power conversion efficiency to 24.18 W/m2 and 2.88%, respectively. Through the RAC primary concentrator and the dual-rod scheme, 29.06 W/m2 in multimode collection efficiency and 3.06% solar-to-laser power conversion efficiency were obtained. Also, TEM00-mode solar laser was improved with the novel three-folding-mirror laser beam merging technique, reaching 16.10 W/m2 of collection efficiency. Finally, a Nd:YAG dual-rod solar laser prototype was designed and built based on the numerical calculations. Experimental advancements were achieved regarding the solar tracking stability of the solar laser emission, reducing the eventual costs of future solar laser systems. The improvement in solar tracking error width at 10% laser power loss was 3.5 times and 1.5 times in its vertical and horizontal solar laser setups, respectively. Compared with the most efficient experimental single-rod solar laser, tracking error enhancement attained with the dual-rod in its vertical and horizontal setups was 23.3 and 10.0 times, respectively. The solar laser beam merging technique is also presented. The research work performed along this thesis and its results are discussed and future perspectives are finally proposed.Nesta dissertação são reportados os avanços tecnológicos em lasers de bombeamento solar e coleção e concentração de energia solar. Novos conhecimentos para melhorar a eficiência geral e a estabilidade de seguimento solar de lasers solares são apresentados, demonstrando novas possibilidades em direção à uma geração de energia sustentável e a uma industria de baixo carbono como uma solução para novos segmentos de inovação tecnológica. Progressos significantes em eficiência de laser solar e estabilidade de seguimento solar foram obtidos com análise numérica. ZEMAX© em modo não-sequencial para o traçado de raios e LASCAD© para análise da cavidade ressonante foram usados para otimizar o design ótico e os parâmetros da cavidade ressonante. 38.2 W/m2 de laser solar multimodo com configuração de bombeamento longitudinal-lateral foi conseguido utilizando um concentrador de anéis (CA). O esquema de dois-cristais com bombeamento lateral aumentou a eficiência de coleção e a eficiência de conversão de potência solar-para-laser multimodo para 24.18 W/m2 e 2.88%, respectivamente. Através do CA como concentrador primário e do esquema de dois-cristais, 29.06 W/m2 em eficiência de coleção em multimodo e 3.06% de eficiência de conversão de potência solar-para-laser foram obtidos. Também o laser solar em modo fundamental foi melhorado com a nova técnica de fusão de feixes laser com três-espelhos, atingindo 16.10 W/m2 de eficiência de coleção. Finalmente, um protótipo de laser solar Nd:YAG de dois-cristais foi desenhado e construído baseado nas simulações numéricas. Avanços experimentais foram atingidos em relação à estabilidade de seguimento solar da emissão de laser solar, reduzindo os eventuais custos de futuros sistemas de laser solar. O melhoramento na largura de erro de seguimento solar a 10% de perda de potência laser foi 3.5 vezes e 1.5 vezes nos seus esquemas vertical e horizontal, respectivamente. Comparado com o mais eficiente laser solar experimental de um cristal, a melhoria conseguida no erro de seguimento com o dois-cristais nos seus esquemas vertical e horizontal foi de 23.3 e 10.0 vezes, respectivamente. A técnica de fusão de feixes laser com três espelhos também é apresentada. O trabalho de pesquisa feito ao longo desta tese e os seus resultados são discutidos e futuras perspectivas são finalmente propostas

Research on solar pumped liquid lasers

A solar pumped liquid laser that can be scaled up to high power (10 mW CW) for space applications was developed. Liquid lasers have the advantage over gases in that they provide much higher lasant densities and thus high-power densities. Liquids also have advantages over solids in that they have much higher damage thresholds and are much cheaper to produce for large scale applications. Among the liquid laser media that are potential candidates for solar pumping, the POC13: Nd sup 3+:ZrC14 liquid was chosen for its high intrinsic efficiency and its relatively good stability against decomposition due to protic contamination. The development of a manufacturing procedure and performance testing of the laser, liquid and the development of an inexpensive large solar concentrator to pump the laser are examined

Quasi-Gaussian Multibeam Solar Laser Station for a Megawatt Solar Furnace

CEECIND/03081/2017An alternative multirod solar side-pumping concept for the production of multiple quasi-Gaussian beams is proposed. This scheme was based on the One-Megawatt solar furnace in Odeillo, France, which collected and concentrated the solar light into a multilayered pyramidal pumping cavity placed at the focal zone. Each layer was comprised of a square array of four laser heads, each composed of a biconic surface that reflected the solar rays towards a Nd:YAG rod fixed inside a fused silica flow tube. A pyramidal reflector was placed inside the pumping cavity to close it and maximize the harness of solar energy. Compared to the previous multibeam solar laser station design for the same solar furnace, considerable alleviation of thermal lensing effects was achieved with the present approach, allowing the improvement of the laser beam quality factors and, consequently, the possibility of a 32-laser-beam generation, each with a quasi-Gaussian profile. For this case, 9.44 kW total laser power was calculated. Additionally, 20.01 kW total multimode laser power was numerically determined, which corresponds to a 10.93 W/m2 collection efficiency and a 2.0% solar-to-laser power conversion efficiency.publishersversionpublishe

High-efficiency solar laser pumping by a ring-array concentrator

Aiming to significantly improve solar laser efficiency, in this thesis, a 20 mm length 5.5 mm diameter Nd:YAG single-crystal rod can be efficiently pumped by highly concentrated solar radiation through a modified ring-array concentrator. Composed of six coaxial parabolic reflective rings and a small diameter Fresnel lens, the 1500 mm diameter modified ring-array concentrator can tightly focus incoming solar radiation into a 5.0 mm full width at half maximum focal spot. An innovative aspherical fused silica concentrator allows further pump light concentration into the Nd:YAG rod at the focal zone. A simple but effective water-cooling scheme within the aspherical concentrator constitutes another highlight of this assembly. Strong dependency of solar laser power on the rim angle of the ring-array concentrator was found through ZEMAX™ and LASCADTM analyses. A continuous-wave solar laser power of 67.8 W at 1064 nm and 38.4 W/m2 collection efficiency was numerically calculated, being 1.22 times more than the previous record. Also, 1.29, 1.03 and 1.85 times improvements in conversion, slope efficiencies and brightness figure of merit, respectively, were numerically achieved. The tracking error influence on solar laser output power was numerically calculated. A simple 1:7 scale model of the ring-array concentrator was also built to verify how the primary focusing performs in direct sunlight

Studies of new media radiation induced laser

Various lasants were investigated especially, 2-iodohepafluoropropane (i-C3F7I) for the direct solar pumped lasers. Optical pumping of iodine laser was achieved using a small flashlamp. Using i-C3F7I as a laser gain medium, threshold inversion density, small signal gain, and laser performance at the elevated temperature were measured. The experimental results and analysis are presented. The iodine laser kinetics of the C3F7I and IBr system were numerically simulated. The concept of a direct solar-pumped laser amplifier using (i-C3F7I) as the laser material was evaluated and several kinetic coefficients for i-C3F7I laser system were reexamined. The results are discussed