Zigzag Multirod Laser Beam Merging Approach for Brighter TEM00-Mode Solar Laser Emission from a Megawatt Solar Furnace

Abstract

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 core-doped Nd:YAG laser rods within a water-cooled pump cavity through a fused silica window. Compared to the previous multibeam solar laser station concepts for the same solar furnace, the present approach can allow the production of high-power TEM00-mode solar laser beams with high beam brightness. An average of 1.06 W TEM00-mode laser power was numerically extracted from each of 1657 rods, resulting in a total of 1.8 kW. More importantly, by mounting 399 rods at a 30° angle of inclination and employing the beam merging technique, a maximum of 5.2 kW total TEM00-mode laser power was numerically extracted from 37 laser beams, averaging 141 W from each merged beam. The highest solar laser beam brightness figure of merit achieved was 148 W, corresponding to an improvement of 23 times in relation to the previous experimental record.

Multirod approach to enhance solar-to-laser conversion efficiency in the Odeillo solar furnace

“…To circumvent hindrances, such as laser beam distortion and rod fracture, the potential of multirod solar-pumped laser systems has been investigated 24 – 33 In these systems, each rod absorbs a portion of the total concentrated solar radiation, leading to less thermal load and waning effects of thermal lensing and thermal stress problems. With the paramount importance of the multirod scheme scalability in mind, multirod laser stations have been proposed for megawatt solar furnaces (MWSFs), namely the ones being operated in Uzbekistan 24 and in France 29 , 30 , 32 .…”

“… – 33 In these systems, each rod absorbs a portion of the total concentrated solar radiation, leading to less thermal load and waning effects of thermal lensing and thermal stress problems. With the paramount importance of the multirod scheme scalability in mind, multirod laser stations have been proposed for megawatt solar furnaces (MWSFs), namely the ones being operated in Uzbekistan 24 and in France 29 , 30 , 32 . In 2008, a side-pumping scheme with five Nd:YAG rods was designed for the Uzbek MWSF, predicting a 1.50 kW laser power production, which corresponds to a 1.3% solar-to-laser power conversion efficiency 24 .…”

“…By placing a solar flux homogenizer at the focus and adopting an end-side-pumping configuration, rods of smaller volume were utilized to efficiently extract TEM00-mode solar laser beams. Still, with a much more complex system of 1657 rods, the highest total multimode laser power of 15.20 kW was numerically attained with solar-to-laser power conversion and collection efficiencies being only 1.52% and 8.3 W/m2, respectively 32 . In this scheme, core-doped Nd:YAG rods were employed instead of conventional ones, as they had already shown their effectiveness in enhancing the brightness of diode-pumped solid-state lasers 34 , 35 .…”

“…With the paramount importance of the multirod scheme scalability in mind, multirod laser stations have been proposed for megawatt solar furnaces (MWSFs), namely the ones being operated in Uzbekistan 24 and in France. 29,30,32 In 2008, a side-pumping scheme with five Nd:YAG rods was designed for the Uzbek MWSF, predicting a 1.50 kW laser power production, which corresponds to a 1.3% solar-to-laser power conversion efficiency. 24 12 years later, after recreating the entirety of the collection and concentration system of the French MWSF of PROMES-CNRS in Zemax® software, a side-pumping scheme with a solar flux homogenizer and 12 Nd:YAG rods of 10 mm diameter and 516 mm length was studied.…”

“…Still, with a much more complex system of 1657 rods, the highest total multimode laser power of 15.20 kW was numerically attained with solar-to-laser power conversion and collection efficiencies being only 1.52% and 8.3 W∕m 2 , respectively. 32 In this scheme, core-doped Nd:YAG rods were employed instead of conventional ones, as they had already shown their effectiveness in enhancing the brightness of diode-pumped solid-state lasers. 34,35 Core-doped rods possess two components: a core, which is the only part that is laser active, and a cladding surrounding it, which has the same properties as the host material and can either be undoped or doped with a different material that efficiently absorbs light at the signal wavelength.…”