Quasi-Cassegrain off-axis concentrator using a corrective hyperbolic-freeform secondary mirror for space solar-powered lasers

Solar-powered lasers (SPLs) offer transformative potential for solar energy utilization, relying on the efficient collection and concentration of sunlight. This study investigates advanced optical design configurations of solar concentrators, emphasizing unobscured off-axis freeform optical designs. A 99 mm diameter off-axis parabolic (OAP) mirror is developed as the primary concentrator. Optical simulations demonstrate the OAP mirror’s ability to concentrate solar power to 8.0 W at its focal point. Fabricated using single-point diamond turning, the OAP achieved high optical accuracy. Validated using phase-shift interferometry, showing peak-to-valley surface deviations of 2.64 µm. Surface profile analysis, using Zernike fringe coefficients, provided detailed insights into surface deviations, which are subsequently integrated into the OAP’s optical design. To address the inherent limitations of off-axis concentrator systems, an unobscured confocal off-axis Quasi-Cassegrain configuration is applied. This innovative two-mirror configuration combines the OAP with a freeform corrective mirror compensating the as-manufactured large primary mirror. This adaptive design and manufacturing process greatly reduces the overall manufacturing cost and risk to produce the large primary mirror with tight tolerance. Instead, we introduce a much smaller secondary mirror to correct the residual aberrations. The system achieves 8.9 W of concentrated power, an 11.25% improvement over conventional designs. The proposed two-mirror system demonstrates substantial potential for advancing concentrating technologies, enabling the development of efficient and reliable SPL systems for space applications.