Dual-beamline electro-optic continuous focal zooming for KrF laser drivers.

Focal zooming is a critical technique for direct-drive inertial confinement fusion (ICF). In this paper, we propose a dual-beamline electro-optic (EO) continuous focal-zooming scheme for KrF laser drivers, capable of delivering nanosecond-scale response and continuously tunable focal-spot diameters over a wide range. In each beamline, wavefront modulation by an EO crystal enables continuous variation of the focal-spot diameter, while switching between the two beamlines extends the overall zooming range beyond the capability of a single element. Numerical simulations demonstrate that the proposed scheme achieves an approximately threefold continuous spot compression while maintaining a well-defined flat-top focal profile and excellent irradiation uniformity within 1% root-mean-square (RMS) nonuniformity. This work provides a viable approach for dynamic irradiation control and enhanced laser-target coupling in high-power KrF laser drivers.