Single-shot, phase-diversity phase retrieval for high-energy beam focal-spot diagnostics

A single-shot, phase-diversity phase-retrieval method is demonstrated for directly characterizing the on-target focal spot at kilojoule energy in the OMEGA 60-beam laser. A 2D holographic grating that introduces diversity focal spots is installed in an existing on-target focal-spot diagnostic to obtain a single-shot diversity focal-spot image. A nonlinear optimization phase-retrieval algorithm with four diversity focal spots is employed to deter-mine modal coefficients for the incident wavefront. The agreement between the measured and calculated focal spots is excellent. This approach can be easily adapted for other high-energy focal-spot diagnostics. (c) 2023 Optica Publishing Group