Seven-rod pumping concept for simultaneous emission of seven TEM00-mode solar laser beams

Abstract

In present-day single-rod/single-beam solar laser systems, the thermal lens effect is a serious issue that 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-parabolic mirror system and a single large laser head. The large laser head consisted of seven fused silica compound parabolic concentrators, which transmitted and focused the concentrated solar radiation to each single-laser rod of small diameter, within a conical cavity, which enabled multiple passages of the pump rays. Consequently, each laser rod was pumped by only one-seventh of the total concentrated solar power, ensuring a significant reduction of the thermal induced effects in the laser rods. 13.3 W∕m 2 TEM 00 -mode solar laser collection efficiency was numerically achieved, representing an enhancement of 1.68 times over the experimental record from a single-rod prototype. 1.80 times improvement in solar-to-TEM 00 -mode laser power conversion efficiency was also registered in relation to the previous experimental record.

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

“…Moreover, the previous four-rod scheme was much more complex, using a quadrangular pyramidal reflector to redirect the focused solar rays towards four laser heads, in comparison to the much simpler single laser head design adopted in the present work. Similar assumptions can be made on the seven-rod scheme proposed by Almeida et al in 2020 [ 33 ]. In this case, the concentrated solar radiation was focused into a single laser head but each one of the seven Nd:YAG rods was pumped within an individual conical cavity, not taking advantage of the shared absorption between rods in the same cavity, and consequently leading to a reduced efficiency.…”

“…Similar to our previous solar laser schemes [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 31 , 32 , 33 , 34 , 35 , 36 ], all the above-mentioned design parameters of the four-rod scheme were firstly optimized by non-sequential ray-tracing ZEMAX ® software to achieve the maximum absorbed pump power for each laser rod, while ensuring an efficient redistribution of pump light to each one. The direct standard solar spectrum for one-and-a-half air mass (AM1.5 D) was used as the reference data for consulting the spectral irradiance (W m −2 nm −1 ) at each wavelength of the solar spectrum [ 50 ].…”

“…Nevertheless, laser output power and its beam quality are strongly influenced by the thermal lensing and thermal stress problems of the single-laser source. To avoid these limitations, solar laser systems based on a multi-rod/multi-beam concept from a single solar laser head have been studied [ 31 , 32 , 33 , 34 , 35 , 36 ]. This is significant for solar laser research, since solar pump rays not completely absorbed by one of the rods can be further absorbed by other rods, leading to more passages through the active media.…”

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

“…It has proven its effectiveness in applications such as welding, brazing, surface texturing [28], microstructuring [29], laser ablation, drilling, and cutting [30,31], achieving more positive outcomes compared to that with the conventional single laser beam. In similar fashion, researchers have been proposing concepts based on the distribution of concentrated radiation among multiple rods [32][33][34][35][36][37][38][39] to abate the thermal stress effects. Through numerical work, multirod laser stations have shown great potential to be used in megawatt solar furnaces (MWSF) [32,36,38].…”

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

“…Even though the reduction of its diameter makes it more thermally resistant, it can severely limit the laser power production. In order to overcome this issue, solar pumping concepts using multiple rods have been proposed, promoting the distribution of concentrated radiation amongst them [22][23][24][25][26][27]. In 2008, a five-rod scheme with a side-pumping configuration was designed for the One-Megawatt solar furnace of Materials Science Institute of Uzbek Academy of Sciences, predicting a laser power production of 1.5 kW and a solar-to-laser power conversion efficiency of 1.3% [22].…”