Solar Laser Power Research Articles

Lowest threshold solar-pumped Ce:Nd:YAG laser with 2.06% solar-to-TEM00 mode laser conversion efficiency

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 concentrate incoming solar power to a 2 mm diameter, 30 mm length Ce:Nd:YAG rod. 1.81 W continuous-wave 1064 nm solar laser output power was measured, corresponding to 3.15% solar-to-laser conversion efficiency, 4.4% laser slope efficiency, and 29.4 W/m2 collection efficiency. More importantly, threshold incoming solar power as low as 16.5 W was achieved, representing a 3.33 times reduction in threshold solar power, as compared to previous record by the parabolic mirror. By using a 0.0855 m2 area Fresnel lens, 2.83 W solar laser power was also measured, leading to 3.56% solar-to-laser conversion efficiency, 4.9% laser slope efficiency, and 33.1 W/m2 collection efficiency. Low threshold incoming solar power of 22.7W was also obtained, representing a 2.42 times reduction in threshold solar power in relation to the previous record. Notably, 1.41 W TEM00 mode solar laser power was also measured by adopting an asymmetric laser resonant cavity, resulting in 2.06% solar-to-TEM00 mode laser conversion efficiency, which, to the best of our knowledge, is 2.61 times larger than the previous record by Nd:YAG medium.

Solar-pumped dual-rod Ce:Nd:YAG laser with 58W continuous-wave output power and 5.1° tracking error compensation width.

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 laser power of 58 W was measured. To the best of our knowledge, this is the highest laser power from a Ce:NdYAG solar laser. Moreover, wide tracking error compensation width of 5.1° in the azimuthal direction was reached, being 4.25 times higher than the previous measurement without solar tracking assistance.

High Brightness Ce:Nd:YAG Solar Laser Pumping Approach with 22.9 W/m2 TEM00-Mode Collection Efficiency

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 the Ce:Nd:YAG laser head was numerically studied by both ZEMAX® v13 and LASCADTM v1 software. Maximum multimode laser power of 99.5 W was computed for the 4.1 mm diameter, 34 mm length grooved rod, corresponding to a collection efficiency of 33.2 W/m2. To extract TEM00-mode solar laser, symmetric and asymmetric optical resonators were investigated. For the 4.1 mm diameter, 34 mm length grooved rod, maximum TEM00-mode solar laser collection efficiency of 22.9 W/m2 and brightness figure of merit of 62.4 W were computed using the symmetric optical resonator. While, for the asymmetric optical resonator, the maximum fundamental mode solar laser collection efficiency of 16.1 W/m2 and brightness figure of merit of 37.3 W were numerically achieved. The asymmetric resonator offered a TEM00-mode laser power lower than the one obtained using the symmetric resonator; however, a collimated laser beam was extracted from the asymmetric resonator, unlike the divergent TEM00-mode laser beam provided by the symmetric resonator. Nevertheless, using both optical resonators, the TEM00-mode Ce:Nd:YAG solar laser power and beam brightness figure of merit were significantly higher than the numerical values obtained by the previous Nd:YAG solar laser considering the same primary concentrator.

Fresnel Lens Solar-Pumped Laser with Four Rods and Beam Merging Technique for Uniform and Stable Emission under Tracking Error Influence

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 aspherical lenses and four semi-cylindrical pump cavities, where the Nd:YAG laser rods were placed, enabling an efficient solar pumping of the laser crystals. A 104.4 W continuous-wave multimode solar laser power was achieved, corresponding to 29.7 W/m2 collection efficiency, which is 1.68 times that of the most efficient experimental Nd:YAG side-pumped solar laser scheme with heliostat–parabolic mirror systems. End-side-pumped configuration has led to the most efficient multimode solar lasers, but it may cause more prejudicial thermal effects, poor beam quality factors and a lack of access to both rod end-faces to optimize the resonant cavity parameters. In the present work, an eight-folding-mirror laser beam merging technique was applied, aiming to attain one laser emission from the four laser rods that consist of the four-rod side-pumping scheme with a higher brightness figure of merit. A 79.8 W multimode laser output power was achieved with this arrangement, corresponding to 22.7 W/m2. The brightness figure of merit was 0.14 W, being 1.6, 21.9 and 15.7 times that of previous experimental Nd:YAG solar lasers pumped by Fresnel lenses. A significant advance in tracking error tolerance was also numerically attained, leading to a 1.5 times enhancement in tracking error width at 10% laser power loss (TEW10%) compared to previous experimental results.

Seven-Grooved-Rod, Side-Pumping Concept for Highly Efficient TEM00-Mode Solar Laser Emission through Fresnel Lenses

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 enhance the efficiency in TEM00-mode laser power production, employing six Fresnel lenses with 10 m2 total collection area for collection and concentration of sunlight. Six folding mirrors redirected the solar rays towards the laser head, composed of six fused silica aspheric lenses and rectangular compound parabolic concentrators paired together for further concentration, and a cylindrical cavity, in which seven Nd:YAG rods were mounted and side-pumped. With conventional rods, total TEM00-mode laser power reached 139.89 W, which is equivalent to 13.99 W/m2 collection efficiency and 1.47% solar-to-TEM00-mode laser power conversion efficiency. More importantly, by implementing rods with grooved sidewalls, the total laser power was increased to 153.29 W, corresponding to 15.33 W/m2 collection and 1.61% conversion efficiencies. The side-pumping configuration and the good thermal performance may ensure that the seven-grooved-rod system has better scalability than other previously proposed schemes.

Fresnel Lens Solar Pumping for Uniform and Stable Emission of Six Sustainable Laser Beams under Non-Continuous Solar Tracking

A multirod solar laser approach is here proposed to attain uniform and stable multibeam emission 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 a light-guide homogenizer and a third-stage conical pump cavity with six Nd:YAG rods. The solar laser system was optimized through numerical analysis in both Zemax® and LASCAD™ software to obtain six 1064 nm laser beams of similar multimode power. To investigate the effect of the homogenizer on the laser performance, the laser head was compared with a similar one that only used the aspherical lens in the second stage. The approach with the light guide attained a slightly lower efficiency than the one without the light guide; however, the tracking error width at 10% laser power loss was higher and, most importantly, only a 2.17% coefficient of variation of the laser power emitted by the six rods at the tracking error angle of ±0.5° was obtained. This is 4.2 times better than the 52.31% obtained with the laser head without the homogenizer and 76 times better than that of the previous numerical work. The light guide is thus essential to ensure uniform and stable solar laser power extraction from all rods even under non-continuous solar tracking, making this prototype the ideal for multibeam laser applications where uniformity and stability of the laser power are indispensable. This renewable multibeam solar laser may replace the classical lamp- and diode-pumped lasers, therefore ensuring a sustainable laser power production pattern for both space and terrestrial applications.

Solar laser pumping approach for both simultaneous and stable multibeam operation under tracking error condition

A solar laser pumping approach to achieve both simultaneous and stable multibeam solar laser operation under solar tracking error condition is proposed here. By using a heliostat, solar radiation is firstly redirected to a parabolic mirror, secondarily concentrated by an aspheric lens, and finally absorbed by four Nd:YAG rods within a pump cavity using a homogenizer. Zemax® and LASCAD™ analysis demonstrate that four simultaneous and stable 1064-nm continuous-wave solar laser emissions with similar multimode power levels can be achieved even with azimuthal solar tracking errors up to ± 0.5 deg. The variation on the multimode solar laser power of the four rods is significantly reduced from 32.38% and 55.52% without the homogenizer to 0.00% and 0.21% with the homogenizer for ± 0.1 deg and ± 0.2 deg azimuthal solar tracking error, respectively. More importantly, simultaneous and stable TEM00 mode solar laser emissions from the four rods are also numerically attained under solar tracking error condition.

Stable emission of solar laser power under non-continuous solar tracking conditions.

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 redirected toward a first-stage parabolic concentrator. At its focus, an aspheric lens further concentrates the solar rays onto five Nd:YAG rods positioned within an elliptical-shaped pump cavity. Numerical analysis using Zemax and LASCAD software showed that the tracking error width at 10% laser power loss for the five 6.5mm diameter and 15mm length rods was 2.20°, which is 50% higher than that of the solar laser in previous non-continuous solar tracking experiments. 2.0% solar-to-laser conversion efficiency was also attained.

Highly Efficient Four-Rod Pumping Approach for the Most Stable Solar Laser Emission.

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. 0.76° tracking error width at 10% laser power loss, and total multimode laser power variation of 0.05% at ±0.1° solar tracking error and 0.30% at ±0.2° solar tracking error were numerically calculated, being 1.27, 74.80 and 21.63 times, respectively, more than the experimental record in solar tracking error compensation capacity attained with a dual-rod side-pumping horizontal prototype pumped by the same heliostat-parabolic system. Additionally, the end-side-pumping configuration of the four-rod solar laser-enabled 43.7 W total multimode solar laser power, leading to 24.7 W/m2 collection efficiency and 2.6% solar-to-laser power conversion efficiency, being 1.75 and 1.44 times, respectively, more than that experimentally obtained from the dual-rod side-pumping prototype. The significant improvement in solar tracking error compensation capacity with a highly efficient end-side-pumping configuration is meaningful because it reduces the cost of high-precision trackers for solar laser applications.

Most efficient simultaneous solar laser emissions from three Ce:Nd:YAG rods within a single pump cavity

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 0.1 at.% Ce:1.1 at.% Nd:YAG laser rods within a single conical pump cavity. For 356 W incoming solar power, 16.5 W continuous-wave total multimode solar laser power was measured, corresponding to 4.64% solar-to-laser conversion efficiency, 41.25 W/m 2 collection efficiency, and 7.64% slope efficiency, which are 1.24, 1.27, and 1.11 times, respectively, higher than previous records by pumping a single 4.5 mm diameter, 35 mm length 0.1 at.%Cr:1.0 at.%Nd:YAG ceramic laser rod. The three-rod Ce:Nd:YAG solar laser also provided 2.13, 2.25 and 1.50 times enhancements in solar-to-laser conversion efficiency, collection efficiency, and slope efficiency, respectively, as compared to previous records by pumping three 3.0 mm diameter, 25 mm length 1.0 at.% Nd:YAG rods within the same single conical pump cavity. • Most efficient simultaneous emissions of three 1064 nm solar laser beams. • 4.64% solar power-to-laser power conversion efficiency attained. • 41.25 W/m 2 solar laser collection efficiency achieved. • 7.64% solar laser slope efficiency was calculated.

Ce:Nd:YAG Solar Laser with 4.5% Solar-to-Laser Conversion Efficiency

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 m2 to end-side pump a Ce (0.1 at%):Nd (1.1 at%):YAG rod of 2.5 mm diameter and 25 mm length. Optimum solar laser design parameters were found through Zemax© non-sequential ray-tracing and LASCAD™ analysis. The utilization of the Ce:Nd:YAG medium with small diameter pumped by a small-scale solar concentrator was essential to significantly enhance the end-side pump solar laser efficiency and thermal performance. For 249 W incoming solar power at an irradiance of 850 W/m2, 11.2 W multimode solar laser power was measured, corresponding to the record solar-to-laser power conversion efficiency of 4.50%, being, to the best of our knowledge, 1.22 times higher than the previous record. Moreover, the highest solar laser collection efficiency of 38.22 W/m2 and slope efficiency of 6.8% were obtained, which are 1.18 and 1.02 times, respectively, higher than the previous records. The lowest threshold solar power of a Ce:Nd:YAG solar-pumped laser is also reported here.

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

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.

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

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.

Highly Efficient Solar Laser Pumping Using a Solar Concentrator Combining a Fresnel Lens and Modified Parabolic Mirror

Solar-pumped lasers (SPLs) allow direct solar-to-laser power conversion, and hence, provide an opportunity to harness a renewable energy source. Herein, we report significant improvements in end-side-pumped solar laser collection efficiency and beam brightness using a novel 1.5-m-diameter compound solar concentrator combining a Fresnel lens and modified parabolic mirror. A key component of this scheme is the off-axis-focused parabolic mirror. An original dual-parabolic pump cavity is another feature. To determine the dependence of the SPL performance on the distance between the focus and central axis of the modified parabolic mirror, several systems with different distances were optimized using TracePro and ASLD software. It was numerically calculated that end-side pumping a 5-mm-diameter, 22-mm-long Nd:YAG crystal rod would generate 74.6 W of continuous-wave solar laser power at a collection efficiency of 42.2 W/m2, i.e., 1.1 times greater than the previous record value. Considering the laser beam quality, a brightness figure of 0.063 W was obtained, which is higher than that of other multimode SPL designs with end-side pumping. Thus, our SPL concentrator offers the possibility of achieving a beam quality as high as that obtainable via side pumping, alongside highly efficient energy conversion, which is characteristic to end-side pumping.

Improving side-pumped solar lasers using ring-array concentrators

ABSTRACT 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 concentrator. In the latter, two thin laser rods were pumped simultaneously. 49.70 W continuous-wave multimode solar laser power, corresponding to 29.06 W/m2 collection efficiency, and 3.06% solar-to-laser power conversion efficiency were numerically attained for the dual-rod side-pumping scheme, being 1.65 and 1.26 times higher than the previous experimental records with Nd:YAG side-pumping configurations. A three-folding-scheme single laser beam technique is presented, enabling a significant improvement of laser beam quality factors.

Seven-Rod Pumping Approach for the Most Efficient Production of TEM00 Mode Solar Laser Power by a Fresnel Lens

Abstract 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, solar pump rays not completely absorbed by one of the seven rods were furtherly absorbed by other rods, ensuring hence a high absorption efficiency and avoiding the serious thermal lensing and thermal stress issues associated with classical large rod solar lasers. Seven individual plane-concave large-mode resonators were adopted to enable a good overlap between solar pump mode and TEM00 laser oscillating mode. By using both zemax® and lascad® software, the maximum total TEM00 mode solar laser power of 54.65 W was numerically calculated by optimizing the radius parameter of the Fresnel lens, the diameter of the laser rod, and the radius of curvature of the laser resonator output mirror. TEM00 mode solar laser collection efficiency of 13.66 W/m2 and solar power-to-TEM00 mode laser power conversion efficiency of 1.44% were calculated, representing substantial enhancements of 4.66 times and 4.38 times, respectively, as compared with previous experimental records of the TEM00 mode solar laser pumped through a Fresnel lens with 0.785 m2 collection area. The feasibility of TEM00 mode solar laser power delivery by hollow-core photonic crystal fibers was finally studied.

STUDY OF Nd: YAG SOLAR LASER OUTPUT PERFORMANCE IN END PUMPING AND SIDE PUMPING CONFIGURATIONS

Since the report of the first sun-pumped solid-state laser, several pumping schemes have been proposed for enhancing the solar-laser performance. Although the most efficient laser systems have end-pumping approaches, side-pumping configurations are very suitable for reducing the thermal loading problems and consequently producing higher laser beam quality. Here we report a study of the Nd: YAG solar-lasers performance by using either end-pumping or side-pumping techniques. The end-pumping configuration provides simultaneously, in multimode regime, the maximum laser power (120 W continuous wave), the highest collection efficiency (32.1 W/m2), the highest slope efficiency (8.9 %), the lowest threshold pump power (192 W) and in monomode operation the highest fundamental-mode collection efficiency (7.9 W/m2) the highest solar laser brightness (6.5 W). However, the side-pumping approach is very preferred for achieving high laser beam quality in monomode operation (M2 < 1.05). Keywords: Solar irradiance; parabolic mirror; Fresnel lenses; solar-pumped laser; end-pumping configuration; side-pumping method; solar-laser power.

Design of a multibeam solar laser station for a megawatt solar furnace

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 face, 12 laser heads were positioned, each of which was composed of a two-dimensional compound parabolic concentrator that focused the uniform solar radiation from the homogenizer’s output to an Nd:YAG rod mounted inside a fused silica flow tube. Each laser rod was pumped by one-twelfth of the total concentrated solar power transmitted through the homogenizer, ensuring a good thermal performance under highly concentrated solar power. A 22.84-kW total multimode solar laser power, corresponding to 12.48-W / m2 collection efficiency and 2.28% solar-to-laser power conversion efficiency, was numerically determined. The latter represents an enhancement of 1.75 times over the previous numerically calculated value for a multirod/multibeam laser scheme based on another one-MWSF near Tashkent, Uzbekistan.

Theoretical Analysis of Prospects of Organic Photovoltaics as a Multi-Functional Solar Cell and Laser Power Converter for Wireless Power Transfer.

Few reports have researched on utilization of laser power conversion systems for wireless power transfer in aeronautical applications. III-V compound semiconductors are commonly used as photovoltaic (PV) power converters in the previous studies. We propose the prospects of using organic absorbers as PV power converters. For laser power conversion to be applied for portable devices, the PV module should be easily processable, thin, low-weight, and printable on flexible substrates. Organic PVs provide all the above advantages, and thus, could serve as a potential candidate for laser power harvesting applications. Moreover, they can also be made transparent, which could be utilized in power harvesting lamination coatings and windows. We had simulated the possibility of using single-junction and tandem photovoltaic structures for 670 nm and 850 nm laser power harvesting. FDTD simulations were conducted to optimize the PV structure in order to maximize the absorption at the laser wavelengths. A maximum PCE of 16.17% for single-junction PV and 24.85% for tandem PV was theoretically obtained.

Simultaneous solar laser emissions from three Nd:YAG rods within a single pump cavity

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 parabolic mirror with 1.0 m2 effective collection area into the laser rods within the pump cavity. 18.3 W multimode solar laser power was measured, resulting in 5.1% laser slope efficiency. 0.036 W laser beam brightness figure of merit was also achieved for each beam, being 9 times more than that of the most efficient solar laser with 32.5 W/m2 collection efficiency. Since the three laser rods were associated with their own 1064 nm output mirrors, it was possible to adjust individually both solar laser output power levels and beam qualities of the three laser beams by adopting different resonant cavity lengths, enabling potential solar laser applications.