Design and optical characterization of a large continuous phase plate for Laser Integration Line and Laser Megajoule facilities

For development of the French Laser Integration Line and the Laser Megajoule, we describe the design and the control of a first 383 mm x 398 mm continuous phase-plate prototype. Extensively used in laser fusion facilities for beam smoothing, this optical component was manufactured by deep etching onto a fused-silica substrate, which led to a phase plate engraved directly onto fused silica, with which good optical performance could be achieved. We demonstrate good agreement between the desired simulated component and the manufactured component in terms of focal spot shape. This demonstration was performed by both interferometric and photometric measurements.