Solar-pumped Radiation-balanced Laser

Abstract

Solar-pumped lasers, predominantly based on neodymium gain media, offer a promising route to renewable laser-energy conversion and space-based photonics; however, their performance has been constrained by thermal loading and limited power scalability. Here, we propose and numerically investigate a solar-pumped ytterbium thin-disk gain medium in combination with a dome concentrator that enables multipass solar pumping and enhanced absorption. The design yields comparably low lasing thresholds for neodymium- and ytterbium-doped media, while ytterbium provides superior power scalability, enabling up to threefold higher output power. We further identify ytterbium-doped medium combined with a spherical concentrator as a viable solar-pumped, radiation-balanced configuration, achieving self-cooled lasing at solar pump intensities of 28.5 kW cm-2 within the 1020-1033 nm window of the solar spectrum. The spherical concentrator increases the averaged fluence of the solar pump while permitting anti-Stokes fluorescence to escape efficiently. These results establish multi-pass, solar-pumped thin-disk ytterbium lasers as a compact, scalable, and sustainable platform for high-performance solar-pumped lasers

Figures (6)

• Figure 1: Comparison of $\text{Nd}^{3+}$ and $\text{Yb}^{3+}$ gain media in a thin-disk geometry. a) Schematic of a single-pass solar-pumped thin-disk laser. b) The output power versus gain medium thickness of the single-pass pumped laser cavity for a 1.1%-doped Nd:YAG and various doping concentrations from 1.1% to 10% for Yb:YAG thin-disk. c) Schematic of a six-pass solar-pumped thin-disk laser. d) The output power versus thickness of a six-pass solar-pumped laser with a 1.1%-doped Nd:YAG and various doping concentrations from 1.1% to 10% for Yb:YAG. The unfiltered solar irradiance of 1367Wm for Nd:YAG and the filtered solar irradiance of 85.8Wm for Yb:YAG are considered for both schemes.
• Figure 2: Dome solar-pumped thin-disk laser. a) Schematic of a dome solar-pumped thin-disk laser. b) The thickness of the crystal versus the output power of the laser for various solar incident angles. The calculation is performed for 1,1%-doped Yb:YAG gain medium. c) The output power of the dome concentrator concept versus the thickness of the gain medium. It is assumed that the solar beam enters the dome at an oblique angle of 75°. d) Temperature distribution on the thin-disk for a 10% Yb-doped gain medium at a thickness of 40µm and solar pump incident angle of 75°.
• Figure 3: Required properties of $\text{Yb}^{3+}$ ions for radiation balanced lasing. a) Absorption and emission cross section of $\mathrm{Yb}^{3+}$. The blue shaded area shows the filtered spectral bandwidth in the solar spectrum from 1020nm to 1033nm to pump the Yb:YAG gain medium for radiation-balanced operation. b) Energy level diagram of the Yb:YAG gain medium in the radiation balance regime. The blue arrows show the pump spectrum, the red arrow is the lasing wavelength, and the green arrows ($\nu_f$) refer to the anti-Stokes emission.
• Figure 4: Required solar spectrum and solar intensity for radiation balanced lasing. a) Wavelength-dependent required intensity to saturate the atomic transition in Yb:YAG gain medium. b) The minimum pump ($i^{\min}_P$) and lasing ($i^{\min}_L$)intensities required to achieve RBL for various pump wavelengths. c) Thermal power density map for pump wavelength $\lambda_P = 1030\nm$ and lasing wavelength $\lambda_L = 1050\nm$. The Red curve represents the exact condition for RBL, and the blue curve illustrates the relationship between normalized pumping and lasing intensities. For this simulation, the crystal length of 1mm with a doping concentration of 5%5440021 and cavity loss of 0.5% is assumed. d) RBL range is defined for solar spectral bandwidth of 1020n m to 1033n m. The blue curve indicates the threshold pump intensity. The orange curve shows the maximum allowed pump intensity for operation in RBL.
• Figure 5: Concept of a solar-pumped Yb:YAG laser including a sphere concentrator operating in the radiation-balanced regime. A spherical concentrator collects and refocuses sunlight onto the gain medium to increase pump fluence, while also enabling efficient extraction of anti-Stokes fluorescence (ASF) in all directions to support radiative cooling. The inner surface of the concentrator is coated for high reflectivity within the 1020nm--1033nm spectral band required for RBL operation, excluding the area for solar input.