Solar-pumped tem00 mode nd:yag laser

These research projects were funded by the Science and Technology Foundation of Portuguese Ministry of Science (PTDC/FIS/103599/2008 and PTDC/FIS/122420/2010), Technology and Higher Education (FCT-MCTES).Here we show a significant advance in solar-pumped laser beam brightness by utilizing a 1.0 m diameter Fresnel lens and a 3 mm diameter Nd:YAG single-crystal rod. The incoming solar radiation is firstly focused by the Fresnel lens on a solar tracker. A large aspheric lens and a 2D-CPC concentrator are then combined to further compress the concentrated solar radiation along the thin laser rod within a V-shaped pumping cavity. 2.3 W cw TEM00 (M2 ? 1.1) solar laser power is finally produced, attaining 1.9 W laser beam brightness figure of merit, which is 6.6 times higher than the previous record. For multimode operation, 8.1 W cw laser power is produced, corresponding to 143% enhancement in collection efficiency.authorsversionpublishe

Highly efficient solar-pumped Nd:YAG laser

This research project is funded by the Science and Technology Foundation of Portuguese Ministry of Science, (PTDC/FIS/103599/2008) Technology and Higher Education (FCT-MCTES).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 single-crystal rod. The incoming solar radiation from the sun is focused by a 0.9 m diameter Fresnel lens. A dielectric totally internally reflecting secondary concentrator is employed to couple the concentrated solar radiation from the focal zone to a 4 mm diameter Nd:YAG rod within a conical pumping cavity. 12.3 W cw laser power is produced, corresponding to 19.3 W/m2 collection efficiency, which is 2.9 times larger than the previous results with Nd:YAG single-crystal medium. Record-high slope efficiency of 3.9% is also registered. Laser beam quality is considerably improved by pumping a 3 mm diameter Nd:YAG rod.publishersversionpublishe

High-power high-brightness solar laser approach for renewable Mg recovery from MgO

Hydrogen and heat energy from the reaction of magnesium with water can be used for engines and fuel cells. However, at least 4000 K is necessary for magnesium oxide reduction. Ultra high brightness solar-pumped lasers become essential to make this renewable process technology efficient and economically competitive. 2.3 mg/kJ solar laser - induced magnesium production efficiency has been achieved by T. Yabe et al., in 2012, by focusing a 53 W solar laser beam on a mixture of MgO with Si as reducing agent. This result is however far from the 12.1 mg/kJ attained with 2 kW/mm2 CO2 laser beam. To improve substantially the solar laser - induced Mg production efficiency, a simple high-power, high brightness Nd:YAG solar laser pumping approach is proposed. The solar radiation is both collected and concentrated by four Fresnel lenses, and redirected towards a Nd:YAG laser head by four plane folding mirrors. A fused-silica secondary concentrator is used to compress the highly concentrated solar radiation to a laser rod. Optimum pumping conditions and laser resonator parameters are found through ZEMAXpublishersversionpublishe

Design of high-brightness TEM00-mode solar-pumped laser for renewable material processing

The conversion of sunlight into laser light by direct solar pumping is of ever-increasing importance because broadband, temporally constant, sunlight is converted into laser light, which can be a source of narrowband, collimated, rapidly pulsed, radiation with the possibility of obtaining extremely high brightness and intensity. Nonlinear processes, such as harmonic generation, might be used to obtain broad wavelength coverage, including the ultraviolet wavelengths, where the solar flux is very weak. The direct excitation of large lasers by sunlight offers the prospect of a drastic reduction in the cost of coherent optical radiation for high average power materials processing. This renewable laser has a large potential for many applications such as high-temperature materials processing, renewable magnesium-hydrogen energy cycle and so on. We propose here a scalable TEM00 mode solar laser pumping scheme, which is composed of four firststage 1.13 m diameter Fresnel lenses with its respective folding mirrors mounted on a two-axis automatic solar tracker. Concentrated solar power at the four focal spots of these Fresnel lenses are focused individually along a common 3.5 mm diameter, 70 mm length Nd:YAG rod via four pairs of second-stage fused-silica spherical lenses and third-stage 2D-CPCs (Compound Parabolic Concentrator), sitting just above the laser rod which is also double-pass pumped by four V-shaped pumping cavities. Distilled water cools both the rod and the concentrators. 15.4 W TEM00 solar laser power is numerically calculated, corresponding to 6.7 times enhancement in laser beam brightness.publishersversionpublishe

Multi-Fresnel lenses pumping approach for improving high-power Nd:YAG solar laser beam quality

These research projects (PTDC/FIS/103599/2008 and PTDC/FIS/122420/2010) were funded by the Science and Technology Foundation of Portuguese Ministry of Science, Technology and Higher Education (FCT-MCTES).To significantly improve the present-day high-power solar laser beam quality, a three-stage multi- Fresnel lenses approach is proposed for side-pumping either a Nd:YAG single-crystal or a core-doped Sm3+ Nd:YAG ceramic rod. Optimum pumping and laser beam parameters are found through ZEMAX and LASCAD numerical analysis. The proposed scheme offers a uniform absorption profile along the rod. 167 W laser power can be achieved, corresponding to 29.3 W/m2 collection efficiency. High brightness figure of merit of 8.34 W is expected for the core-doped rod within a convex-concave resonator, which is 1300 times higher than that of the most-recent high-power solar laser.authorsversionpublishe

Characterization of loop seal in a complex circulating fluidized bed system

Loop seal is widely used in circulating fluidized bed systems to transport solids from high pressure reactor to low pressure reactor. It also found applications in complex systems with multiple reactors. The functions of the loop seal include circulating solids between reactors with desired solids flow rate, preventing gas leak from either reactor, and providing pressure balance for the proper operation of the system. The proper design and sizing of the loop seal are necessary so that the operation of loop seal is not to disturb the desired, independent operation of the reactors. Despite its extensive applications, the systematic, experimental studies that characterize the loop seal operation in the complex reactor systems are limited. Among the available studies, the particles used are mainly Geldart group A and group B particles. Little is conducted on experiments with Geldart Group D particles. This paper examines the operation of solids through a loop seal in a complex circulating fluidized bed system using Geldart group D particles. The circulating fluidized bed has two reactors whose operational conditions are controlled independently, with a loop seal placed between them. Besides the loop seal and the two reactors, the CFB system also includes a riser, a cyclone, a solids receiver, and standpipes. The solids inlet in the supply chamber of the loop seal is connected to the bottom of the standpipe, while the solids outlet in the return chamber is connected to the solids inlet of a dense phase fluidized bed reactor. A gas outlet with a valve and a gas flowmeter is designed to be located at the top of the return chamber to control the gas flow rate flowing into the fluidized bed reactor downstream the loop seal. The rectangular supply chamber has a dimension of 25 mm x 75 mm x 150 mm and the square return chamber is 75 mm × 75 mm × 300 mm. The pressure profile of the system is recorded using differential pressure gauges and pressure gauges are installed throughout the system. The solids circulation rate of the system is measured using a solids bypassing system connected between the bottom of the system and the top of the standpipe. Effects of operating parameters, such as supply chamber gas flow rate, return chamber fluidization velocity, and gas flow rate from the gas outlet of return chamber, on the operation of the circulating fluidized bed system, including the solids circulation rate and the system pressure balance are also analyzed and discussed

Hydrodynamics of chemical looping combustion systems: Effects of reactor design parameters

Chemical looping combustion (CLC) has been considered a transformational technology for the carbon dioxide (CO2) capture in power plants. Extensive research has been conducted on the selection and preparation of oxygen carrier (OC) materials, their production and characterization, CLC process development, and reactor system demonstrations from bench to pilot scales. Different configurations of CLC system have been proposed and tested, such as interconnected circulating fluidized bed (CFB) reactor systems, CFB with counter-current moving bed reactor systems, and fixed bed reactor systems. Despite considerable research efforts on the development of CLC systems, the analysis of the effects of hydrodynamic characteristics of OC particles, such as particle size, density and support content, on the design and operation of the CLC system is still lacking. Further, major operational parameters that continue to be in need of exploration include the control of the solids circulation rate of the system, pressure balance and profile of the system, and the gas sealing from the interconnected reactors. This study examines the inter-relationships between the hydrodynamics and kinetics characteristics of the OC particles and the operating conditions of the reactors, along with the reaction and heat management of the system. The design principle that is applied to sizing the reactor system is developed. Parametric effects on the system performance due to the variation of particle parameters, reactor size, system pressure, and operating conditions are simulated and analyzed

Comparative study of Cr:Nd:YAG and Nd:YAG solar laser performances

To improve the efficiency of Nd3+-doped YAG solar laser, cross-pumped Cr3+ and Nd3+ co-doped YAG ceramic material has attracted more attentions in recent years. The sensitizer Cr3+ ions have broad absorption bands in the visible region. Despite the interests in Cr:Nd:YAG ceramic medium, researchers have achieved significant laser efficiencies with different Nd:YAG single-crystal rods. While it is clear about the effectiveness of Nd:YAG single-crystal rods for solar laser operation, there still exist some concerns about the advantages of Cr:Nd:YAG ceramics in solar-pumped lasers. A 0.9 m diameter Fresnel lens is used as an economical solar collector. A 4 mm diameter, 25 mm length 1.0 at% Nd:YAG single-crystal rod and a 0.1 at% Cr: 1.0 at% Nd:YAG ceramic rod are pumped alternatively within a conical cavity through a secondary concentrator. With the Nd:YAG rod, the maximum laser power is 12.3 W, corresponding to 19.3 W/m2 collection efficiency. With the Cr:Nd:YAG ceramic rod, the maximum laser power is 13.5 W, corresponding to 21.2 W/m2 collection efficiency. This result is, to the best of our knowledge, the highest collection efficiency achieved with Cr:Nd:YAG ceramic medium. There is also a 109% increase in slope efficiency. In summary, we have experimentally observed a moderate, but not significant, advantage of Cr:Nd:YAG ceramics over Nd:YAG single-crystal medium in both solar laser conversion and slope efficiency.authorsversionpublishe

Core-doped Nd:YAG disk solar laser uniformly pumped by six Fresnel lenses

A novel solar laser uniformly pumped by six Fresnel lenses is proposed here. The incident solar radiation is firstly collected and concentrated by six 0.8 m diameter Fresnel lenses and then reflected by other six plane mirrors to a central focal zone, where a laser head is mounted. About 2.5 kW solar power with 3.5 W/mm2 peak solar flux can be achieved in the focal zone. The laser head is composed of a fused silica six-sphere type secondary concentrator that further compresses the concentrated solar power from the six Fresnel lenses-plane mirrors to a core-doped YAG Nd3+:YAG ceramic disk. Optimum pumping parameters and solar laser output powers are found through ZEMAX non-sequential ray-tracing and LASCAD laser cavity analysis, respectively. The laser resonant cavity is formed by a PR 1064 nm output coupler and a HR 1064 nm plane reflector. An 8 mm diameter central hole is drilled through the six-sphere type concentrator to allow the extraction of laser power from the disk. Since only 16 % of the useful solar power is absorbed by the Nd:YAG medium, for 950 W/m2 of terrestrial solar irradiation, the effective solar pump power of 456 W is assumed in ray-tracing analysis. 72.2 W of multimode laser power is predicted for an 8 mm diameter gain medium embedded within a conical undoped YAG cladding, reaching the collection efficiency of 24.1 W/m2. M2 = 16.6 is numerically calculated, corresponding to the brightness figure of merit of 0.26 W. A near uniform absorbed pump profile is achieved.authorsversionpublishe