Solar-pumped laser is a device that directly converts sunlight into laser light, holding promising applications in fields such as space laser communication, space laser wireless energy transmission, chemical energy cycling, and material processing. The structure of a solar-pumped laser is typically divided into three major components: a sunlight concentration device, a pumping cavity, and a laser gain medium. Existing research has made certain advancements in the design methods for the size and pumping structure of the gain medium in solar-pumped lasers. However, the intrinsic correlation between the size of the laser and its laser output power has not yet been fully explored. When designing lasers for specific output power requirements, reliance is often placed on empirically selected sizes, leading to frequent mismatches between laser size and desired output power. For example, lasers may be excessively bulky without a corresponding increase in output power, or they may have moderate sizes but suffer from inefficient performance. Due to the lack of a systematic theoretical framework to guide the size design of lasers in addressing these issues, a model of a solar-pumped laser incorporating Fresnel lenses and a liquid optical waveguide structure is established based on existing research foundations. This model is used to explore the potential correlation mechanism between laser output power and laser size, providing a scientific basis for designing more efficient and compact solar-pumped lasers.A simulation model for a solar-pumped solid-state laser with a liquid optical waveguide structure, incorporating Fresnel lenses, is constructed, with corresponding materials assigned based on structural characteristics. Simulations are conducted for Fresnel lenses with diameters of 400, 600, 800, 1000, 1200, 1500, 1800 mm by varying their sizes. Optical ray tracing software is utilized to obtain the optimal sizes of the quartz tube and metal conical cavity for each Fresnel lens diameter. Furthermore, the optimal length range of the crystal rod is theoretically calculated using formulas, and the precise optimal length is determined using the laser simulation software ASLD. Finally, based on the obtained optimal sizes of the quartz tube, metal conical cavity, and crystal rod for different Fresnel lens diameters, the theoretical laser output power is calculated using ASLD software.The solar-pumped laser system is simulated using optical tracing software, yielding fitting curves between the optimal dimensions of the quartz tube, the optimal input aperture of the metal conical cavity, and the diameter of the Fresnel lens (Fig.3). Additionally, the optimal length of the crystal rod as a function of the Fresnel lens diameter is determined using the laser simulation software ASLD (Fig.5). Based on the optimal dimensions of each optical component, further simulations are conducted to obtain the fitting curve between the laser output power and the Fresnel lens diameter (Fig.6). The results show that when the relative aperture of the Fresnel lens is 1, the optimal dimensions of the crystal rod, quartz tube, and metal conical cavity increase as the Fresnel lens diameter increases. This indicates that as the diameter of the lens increases, the optical flux incident on the system is enhanced, necessitating adjustments in the dimensions of the optical components to maintain optimal optical performance. Furthermore, by varying the relative aperture of the Fresnel lenses, simulations are conducted to calculate the relationship between laser output power and Fresnel lens diameter. The results indicated that the laser output power increased with the increase in the relative aperture of the Fresnel lenses (Fig.7).A model of a solar-pumped laser based on Fresnel lenses and a liquid optical waveguide structure is constructed to investigate the relationship between the sizes of quartz tubes, metal conical cavities, crystal rods, and Fresnel lenses. Through simulation calculations using various sizes of Fresnel lenses, a fitting curve is obtained that relates output power to the diameter of the Fresnel lens. When the relative aperture of the Fresnel lens is 1, the optimal sizes of the crystal rod, quartz tube, and metal conical cavity increase with the diameter of the Fresnel lens. Based on these optimal sizes, the simulated laser output power increases with the diameter of the Fresnel lens, exhibiting an upward parabolic trend with an open upper end. This paper theoretically establishes the relationship between the size of the Fresnel lens and the output laser power, providing guidance for the design of solar-pumped lasers.