Far-Field Spot Reshaping with Phase-Front Optics for Plasma Experiments

Today, in the high-intensity lasers used for plasma experiments, it is essential to have a controlled envelope for optical absorption in the target designs. Since the 1980s, distributed phase plates (DPP’s) have been widely used as far-field spot-shape control. This poster will describe the DPP design method with examples presented for the Helmholtz International Beamline for Extreme Fields Diode Pumped Optical Laser for Experiments (DiPOLE) 100X. The DiPOLE system plans an upgrade for controlled spot-shape illumination to achieve optimal high-intensity conditions for a variety of experiments at various target sizes. The objective of this project is to create three DPP’s crafted to shape 500-mm, 250-mm, and 100‑mm spots, respectively. Zhizhoo’ was the primary design tool. The contoured-glass DPP design tool Zhizhoo’ adapts to any coherent optical beamline to craft the quasi-random near-field phase optic capable of custom tailoring the prescribed spot-shape envelope on a target in the far field. Zhizhoo’ employs an advanced, adaptive Fourier-transform-based feedback loop with phase unwrapping to craft DPP’s. The DPP controls the distribution of speckle in the far field via phase-front control of the near field, which conforms to any requisite envelope of the laser facility. Detailed design elements such as spatial-frequency controls of the DPP phase object will be discussed and how they affect the design process. As a finished product, less than 1% error along the uniform profile was observed for the DiPOLE DPP designs. As a result of the high efficiency of these designs, DiPOLE will be able to conduct high-energy-density experiments with increased laser performance.