Dawei Liang

Universidade NOVA de Lisboa | NOVA · Department of Physics

Fiber-optic solar energy transmission and concentration provide a flexible way of handling concentrated solar energy. The high flux solar energy transmission by a flexible fiber-optic bundle and the research on the associated compound parabolic concentrator will largely expand the existing field of applications of solar energy concentrators. We rep...

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 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 t...

We report here a significant progress in solar laser slope efficiency by end-side-pumping a 4.5 mm diameter, 35 mm length Cr:Nd:YAG ceramic rod with a 1.0 m 2 effective collection area heliostat-parabolic mirror solar energy concentration system. A novel fused silica liquid light guide lens with unique water cooling approach was used to efficiently...

We report here, to the best of our knowledge, the most efficient simultaneous emissions of three continuous-wave 1064 nm solar laser beams. A fused silica aspheric lens was used to couple the concentrated solar radiation from the focal zone of a 0.4 m 2 effective collection area primary parabolic mirror into three 2.5 mm diameter, 25 mm length 0.1a...

The recent progress in solar-pumped laser with Fresnel lens and Cr:Nd:YAG ceramic medium has revitalized solar laser researches, revealing a promising future for renewable reduction of magnesium from magnesium oxide. Here we show a big advance in solar laser collection efficiency by utilizing an economical Fresnel lens and a most widely used Nd:YAG...

One of the major goals of solar-pumped lasers is to improve TEM00-mode collection and conversion efficiencies. Several studies have explored multi-rod designs with the aim of enhancing laser output and thermal management by distributing the absorbed solar energy across multiple rods. In this work, a concept was introduced comprising four Fresnel l...

A multirod Ce:Nd:YAG solar laser approach, using a Fresnel lens as primary concentrator, is here proposed with the aim of considerably increasing the efficiency of solar-pumped lasers. Fresnel lens is cost-effective, rendering solar lasers to be more economically competitive. Collected and concentrated solar pumping radiation by the Fresnel lens wa...

In this paper, we report a numerical study of high power Nd:YAG solar laser approach pumped through off-axis parabolic concentrators. Six off-axis parabolic mirrors with 15 m² total collection area were used to collect and focus the solar energy towards six 2V-shaped pump cavities, within which a 120 mm length, 7.5 mm diameter Nd:YAG laser crystal...

TEM00-mode operation is a requirement in many laser-based applications due to the small divergence and high-power density of the emitted laser beam. A solar laser scheme was designed and numerically studied with the goal of increasing the solar-to-laser power conversion efficiency in TEM00-mode operation. Collection and primary concentration of sun...

We present here a compact end-side pumped solar laser concept designed to enhance efficiency in both multimode and TEM00-mode operations. The primary concentrator, a 1.0 m diameter off-axis parabolic mirror, efficiently collects and focuses solar rays into the laser head, which consists of a large fused-silica aspheric lens secondary concentrator,...

A solar-pumped laser with bulk active medium generally requires a considerable amount of concentrated solar power for initiating laser emission. In previous work, 54.9 W threshold incoming solar power was found for a Ce:Nd:YAG solar laser by a 0.075 m2 effective area parabolic mirror. In the present work, a 0.0615 m2 area Fresnel lens was used to c...

Progress in solar-pumped lasers within the framework of SFERA Programs

Improving the TEM00-mode laser efficiency is one of the main goals in solar laser research, motivated by the significant importance these high-quality beams hold for fields such as materials processing. A seven-rod concept was designed to enhance the TEM00-mode solar laser efficiency through the adoption of Ce:Nd:YAG active media. Collection and co...

The pursuit of high-power solar laser systems with high efficiency and capacity for large tracking error compensation is determinant for the applicability of this renewable technology. A side-pumped dual-rod Ce:Nd:YAG solar laser was developed and tested at the focus of a 2 m diameter parabolic concentrator. Maximum continuous-wave total solar lase...

Laser beams with doughnut-shaped profile have garnered much attention for their contribution in trapping nanoparticles and improving the scanning speed during laser-based 3D metal print-ing. For this reason, the production of a doughnut-shaped solar laser beam by using end-side-pumping a Ce:Nd:YAG rod with a small reflective parabolic collector, wa...

Conventional solar-pumped lasers rely on expensive and highly accurate solar tracking systems, which present a significant economic barrier to both solar laser research and practical applications. To address this challenge, an end-side-pumped four-rod solar laser head was designed and built for testing at PROMES-CNRS. Solar radiation was collected...

The utilization of TEM00 mode laser beams is critical in precise material processing, optical communication, and high-resolution imaging. While TEM00 mode solar laser beams have been achieved, the need for a highly accurate and continuously operating solar tracking system presents significant challenges. A solar laser pumping approach is here propo...

Classical solar-pumped lasers often demand a significant amount of concentrated solar power for laser emission, which is only attainable under clear sky condition, limiting their applicability. In this research, we report the first solar laser emission at very low threshold solar power under cloudy sky condition by end-side-pumping a 2.5 mm diamete...

A compact side-pumped solar laser design using a Ce:Nd:YAG laser medium is here proposed to improve the TEM00-mode solar laser output performance, more specifically the beam brightness. The solar laser performance of Ce:Nd:YAG laser head was numerically studied by both ZEMAX® and LASCADTM software. Maximum multimode laser power of 99.5 W was comput...

Significant numerical improvements in Fresnel lens Nd:YAG solar laser collection efficiency, laser quality factors and tracking error compensation capacity by two Fresnel lenses as primary solar concentrators are reported here. A Nd:YAG four-rod side-pumping configuration was investigated. The four-rod side-pumping scheme consisted of two large asp...

Low-cost, lightweight, and easily available Fresnel lenses are a more alluring choice for solar laser power production, when compared to the costly and complex heliostat-parabolic mirror systems. Therefore, a seven-rod solar laser head was designed and numerically studied to en-hance the efficiency in TEM00-mode laser power production, employing si...

A multirod solar laser approach is here proposed to attain uniform and stable multibeam emis-sion under non-continuous solar tracking. A Fresnel lens was used as the primary concentrator. The laser head was composed of a second-stage aspherical lens with light-guide homogenizer, and a third-stage conical pump cavity with six Nd:YAG rods. The solar...

Properties of laser radiation and photons are firstly introduced. Planck´s law, Stefan-Boltzmann’s law and Wien´s law are then presented. Spontaneous emission, stimulated absorption, stimulated emission, Einstein coefficients are explained, leading to the definition of important parameters such as laser gain and stimulated emission cross section. U...

This textbook is a comprehensive review of many different areas in solar-pumped lasers design and characterization. It enables readers to develop their skills in general solid-state laser design and solar collector design and provides numerous solved exercises at the end of each chapter to further this development. This book begins by introducing...

In this chapter, the numerical tools for solid-state laser design are introduced. Non-sequential Zemax® ray-tracing analysis is first explained for the optimization of solid-state laser design parameters. Laser cavity analysis and design (LASCAD™) software is also addressed for the evaluation of the laser output performance. An example of numerical...

Milestone multimode solar-pumped laser designs and their laser output performances are introduced in this chapter. Since the knowledge of imaging, and non-imaging primary, secondary and tertiary concentrators are vital for successful solar laser designs, Zemax@ and LASCAD™ numerical analysis examples are provided in order to ensure student’s clear...

A solar laser pumping approach to achieve both simultaneous and stable multi-beam solar laser operation under solar tracking error condition is proposed here. By using a heliostat, solar radiation was firstly redirected to a parabolic mirror, secondarily concentrated by an aspheric lens, and finally absorbed by four Nd:YAG rods within a pump cavity...

Solar laser technology typically requires a highly accurate solar tracking system that operates continuously, which increases energy consumption and reduces the system’s lifetime. We propose a multi-rod solar laser pumping approach to enhance solar laser stability under non-continuous solar tracking conditions. Using a heliostat, solar radiation is...

. In this paper, a four-rod/four-TEM00-mode beam off-axis parabolic mirror solar pumping concept is proposed. Four off-axis parabolic mirrors with 10 m² total collection area were used as the primary solar concentrators to pump four 3.1 mm diameter, 84 mm length Nd:YAG rods within four 2V-shaped pump cavities through four secondary fused-silica asp...

Challenge and research trends of primary and secondary solar concentrators are key issues for advanced solar energy research. The main purpose of the book is therefore to present some of the most recent developments related to solar concentrators. This book is designed to provide the readers a better understanding of solar concentrators and their i...

It is reported here a large improvement in numerically calculated TEM00-mode side-pumped solar laser efficiency, and brightness figure-of-merit by pumping two thin Nd:YAG laser rods simultaneously with a ring-array solar energy primary concentrator. Two side-pumping configurations were investigated. A single-rod configuration was used to pump a typ...

A seven-rod solar laser head was conceptualized and numerically studied to improve the tracking error compensation capacity and power stability in end-side-pumping schemes. It was composed of a first-stage heliostat-parabolic mirror system, a second-stage fused silica aspheric lens and a third-stage conical pumping cavity, within which seven Nd:YAG...

A multirod solar laser station for the megawatt solar furnace in Odeillo, France, was conceptualized and numerically studied to improve the solar-to-laser power conversion efficiency. 18 heliostats from the 63-heliostat field were selected, obtaining 347 kW of solar power at its focus. There, a two-dimensional compound parabolic concentrator furthe...

We report a significant numerical improvement in multi-rod laser efficiency, with an enhanced solar tracking error compensation capacity for a heliostat-parabolic system. The solar laser head was composed of a fused silica conical lens and a single conical pump cavity ensuring multiple passes through four 4.55 mm diameter, 15 mm length Nd:YAG rods....

We present here the first experimental results of tracking error compensation capacity of a solar-pumped laser, with a largely enhanced tracking error tolerance achieved by pumping two laser rods simultaneously. A large aspherical fused silica lens, with an input face of 46 mm radius of curvature and 84 mm diameter, provided an efficient focusing o...

The efficiency potential of a small-size solar-pumped laser is studied here. The solar laser head was composed of a fused silica aspheric lens and a conical pump cavity, which coupled and redistributed the concentrated solar radiation from the focal zone of a parabolic mirror with an effective collection area of 0.293 m 2 to end-side pump a Ce(0.1...

We report here a significant enhancement in side-pumped solar laser collection efficiency and solar-to-laser conversion efficiency by a ring-array primary concentrator. A single and a dual-rod side-pumping configuration were numerically investigated. In the former, a thick laser rod was pumped with the full collection area of the ring-array solar c...

The solar laser power scaling potential of side-pumped Ce:Nd:YAG solar laser through a rectangular fused silica light guide was investigated by using a 2 m diameter parabolic con-centrator. The laser head was formed by the light guide and a V-shaped pump cavity to effi-ciently couple and redistribute the concentrated solar radiation from the parabo...

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 h...

A novel three-dimensional elliptical shape Fresnel lens (ESFL) analytical model is presented to evaluate and maximize the solar energy concentration of Fresnel-lens-based solar concentrators. AutoCAD, Zemax and Ansys software were used for the ESFL design, performance evaluation and temperature calculation, respectively. Contrary to the previous mo...

A seven-rod/seven-TEM00 mode beam Fresnel lens solar laser pumping approach is here proposed. The Fresnel lens with 4.0 m2 collection area was used as the primary solar concentrator to pump seven 2.5 mm diameter, 15 mm length Nd:YAG rods within a conical pump cavity through a secondary fused silica aspheric concentrator. Within the pump cavity, sol...

Aside from the industry-standard Gaussian intensity profile, top hat and non-conventional laser beam shapes, such as doughnut-shaped profile, are ever more required. The top hat laser beam profile is well-known for uniformly irradiate the target material, significantly reducing the heat affected zones, typical of Gaussian laser irradiation, whereas...

An alternative multirod solar laser end-side-pumping concept, based on the megawatt solar furnace in France, is proposed to significantly improve the TEM00-mode solar laser output power level and its beam brightness through a novel zigzag beam merging technique. A solar flux homogenizer was used to deliver nearly the same pump power to multiple cor...

Lamp-pumped laser systems have been widely applied in research and industry. However, one of the major bottleneck issues in lamp-pumped laser development resides in its low electrical input-to-TEM00 mode laser conversion efficiency. Here is proposed a four-lamp/four-rod pumping concept to substantially increase electrical power to TEM00 mode laser...

Laser side-pumping approach is an extremely attractive configuration for many laser applications. Through this approach, the laser beam can be generated in the lowest possible spatial modes, with the highest beam brightness and quality. In this study, a significant improvement in the solar laser output power and collection efficiency of a side-pump...

The maximum achievable solar concentration of a single reflective primary parabolic mirror is limited by its physical aspect ratio. The maximum concentration of a single refractive Fresnel lens is also largely limited by its chromatic aberration. To resolve these shortcomings, a ring-array concentrator (RAC) analytical model with variable aspect ra...

In this paper, we report a numerical study of a side-pumped Nd:YAG solar laser through a Ring-Array Concentrator system. This study consists in optimizing a 1.5 m diameter RAC system, a 3V-shaped pump cavity within which a 4 mm diameter, 30 mm length Nd:YAG single-crystal laser rod was mounted and a laser resonator parameters by using ZEMAX © and L...

An 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 a...

A significant advancement in the Ce:Nd:YAG solar laser performance using a side-pumping configuration is reported here. A solar laser head was composed of a double-stage semispherical lens and a trapezoidal-shaped pumping cavity, which coupled and redistributed the concentrated solar radiation from the focal zone of a parabolic mirror into a laser...

A compact side-pumped solar laser design is proposed to improve the TEM00-mode solar laser output performance substantially. A double-stage secondary concentrator was composed of a rectangular hollow pipe and a 2V-shaped dry pump cavity, which couples and redistributes the concentrated solar radiation from the focal zone of a 2 m diameter parabolic...

Low lamp input-to-TEM00 mode laser output conversion efficiency and strong thermal lensing effects are bottleneck issues in commercially available single-rod/single-beam lamp-pumped lasers. A six-rod/six-beam concept is here proposed to substantially enhance lamp input-to-TEM00 mode laser output conversion efficiency. A 4 kW single thick arc lamp w...

A conversão directa de radiação solar em radiação laser tem ganho uma importância cada vez maior ao longo dos anos. Os lasers bombeados por luz solar fornecem soluções eficazes e ecológicas para a produção de radiação laser, tornando-se numa opção viável em locais com elevada irradiância solar e com poucas fontes de energia disponíveis. Um dos prin...

In present-day single-rod/single-beam solar laser systems, the thermal lens effect is a serious issue which limits its ability for a scale-up to higher powers and improved beam quality. Aiming at resolving this shortcoming, the concept of a seven-rod/seven-beam solar pumping scheme is proposed. This scheme was composed of a first stage heliostat-pa...

A multirod solar side-pumping concept is proposed to study the feasibility of multirod/multibeam laser systems in large-sized solar furnaces. This scheme was based on the one-megawatt solar furnace (MWSF) in Odeillo, France, which collected and concentrated solar rays into an input face of a solar homogenizer placed at the focal zone. At its output...

We report here a significant numerical improvement in side-pumped solar laser collection efficiency and solar-to-laser conversion efficiency, with an enhanced tracking error compensation capacity. Two side-pumped configurations, a single-rod and a dual-rod scheme were studied. The former pumped a thick laser rod with the full collection area of a p...

We report here, to the best of our knowledge, the first simultaneous emission of three continuous-wave solar laser beams by end-side-pumping three 3.0 mm diameter, 25 mm length Nd:YAG single-crystal rods within a single conical pump cavity. An aspheric fused silica lens was used to couple the concentrated solar radiation from the focal zone of a pa...

The first emission of a Ce:Nd:YAG solar-pumped laser is reported here, to the best of our knowledge. A solar laser head was composed of a fused silica liquid light guide lens and a conical pump cavity, which coupled and redistributed the concentrated solar radiation from the focal zone of a parabolic mirror into a Ce:Nd:YAG laser rod. The laser out...

A single ring-array concentrator solar furnace unit was firstly modeled analytically, and then optimized numerically by ZEMAX ® and ANSYS ® software, reaching a temperature of 3778 K, nearly equivalent to that of a medium size solar furnace with 3.14 m 2 collection area. A novel three-dimensional ring array concentrator solar furnace was subsequent...

We present here a tracking error compensation concept in solar-pumped lasers, by pumping two thin laser rods simultaneously, each rod by a half of solar collector area instead of the mostly used scheme with one thick rod pumped by a full solar collector area. A semicylindrical fused silica lens allowed an efficient focusing of the concentrated sola...

To compare the penetration effect of both 1064 nm solar laser and concentrated solar radiations on biological tissue, ex vivo experiments were performed on chicken breast samples with similar incident doses. A 1064 nm Nd:YAG solar laser and a simple solar concentrator were firstly developed, both capable of emitting 10 W light power. Two square cro...

We propose here a novel concept to a large improvement in TEM 00 -mode side-pumped solar laser collection, conversion efficiencies, and brightness figure of merit by pumping two thin laser rods simultaneously, each rod being pumped by half of the solar collector area instead of today’s one thick rod scheme pumped by the full solar collector area. A...

The authors report here a significant progress in side-pumped solar laser slope efficiency by pumping a 3.0 mm diameter, 30 mm length Nd:YAG single-crystal laser rod through a heliostat-parabolic mirror solar energy collection and concentration system with 0.9 m 2 effective collection area. A large fused silica aspheric lens allowed an efficient fo...

In this paper, a doughnut-shaped solar laser beam from a Nd:YAG rod pumped through a heliostat-parabolic mirror system is reported. A solar laser head was composed of a fused silica liquid light guide lens and a conical pump cavity, within which a 4 mm diameter, 35 mm length Nd:YAG single-crystal rod was efficiently end-side-pumped. Multimode solar...

A four-rod solar pumping concept is here proposed for the significant improvement in TEM00-mode solar laser performance. A quadrangular pyramidal reflector was used to separate the focused solar rays from a 2.0 m diameter parabolic mirror into four focal spots. Four laser heads, each one consisted of a double-stage biconical lens/conical pump cavit...

We demonstrated a solar-pumped laser with a heliostat-parabolic mirror system. A designed conical pump cavity with a water-filled quartz tube lens was used to couple efficiently the concentrated solar radiation from the focal zone of the primary concentrator into a 5.5-mm-diameter, 95-mm-length grooved Nd:YAG crystal rod within a gold-plated conica...

A non-Gaussian beam profile such as a doughnut-shaped beam enables novel fundamental insights in light-matter interactions and different approaches to modifying materials through laser-based processing. We report here, to the best of our knowledge, the first emission of a doughnut-shaped solar laser beam from a side-pumped grooved Nd:YAG laser rod...

We report here a compact pumping scheme for achieving large improvement in collection and conversion efficiency of a Nd:YAG solar-pumped laser by an innovative ring-array solar concentrator. An aspheric fused silica lens was used to further concentrate the solar radiation from the focal region of the 1.5 m diameter ring-array concentrator to a 5.0...

To improve TEM00-mode solar-pumped laser output power stability, a monolithic fused silica twisted light guide was firstly produced and then combined with both a 2D-CPC (Compound Parabolic Concentrator) and a 2V-shaped cavity to achieve uniform pumping along a 3 mm diameter, 50 mm length, 1.0 at.% Nd3+: YAG rod through an heliostat-parabolic mirror...

To improve the output beam stability of a TEM00-mode solar-pumped laser, a twisted fused silica light-guide was used to achieve uniform pumping along a 3 mm diameter and 50 mm length Nd:YAG rod. The concentrated solar power at the focal spot of a primary parabolic mirror with 1.18 m2 effective collection area was efficiently coupled to the entranc...

1064 nm solar laser achieves record power output and efficiency With applications in remote sensing from space, wireless power laser beaming, asteroid deflection, and fuel-free photonic thrusters, lasers that emit energy directly through the conversion of sunlight-called solar-pumped lasers (http://www.laserfocusworld.com/articles/print/volume-49/i...