Green light (2$\omega$) has the potential to drive ignition target for laserfusion with significantly more energy than blue light (3$\omega$) and arelatively higher damage threshold for the optic components in the final opticassembly, but it has issues of a relatively low laser to x-ray conversionefficiency and a hard x-ray spectrum as compared to 3$\omega$. In this paper,we propose to drive a foam hohlraum wall with an ignition laser pulse by takinga 4$\omega$ laser at the pre-pulse and a 2$\omega$ laser at the main-pulse,called as 4$\omega$ - 2$\omega$ ignition pulse. This novel design has thefollowing advantages: (1) benefiting from 2$\omega$ of its relatively highenergy output and low damage threshold during main-pulse, (2) benefiting fromfoam in its relatively high laser to x-ray conversion efficiency and relativelylow M-band fraction in re-emission, (3) benefiting from 4$\omega$ of its lowLPI during pre-pulse. From our 1D simulations with Au material, the laser tox-ray conversion in a foam driven by 4$\omega$ - 2$\omega$ pulse has anincrease of $28\%$ as compared to a solid target driven by 3$\omega$ with thesame pulse shape. The relatively thin optical depth of foam is one of the mainreasons for the increase of laser to x-ray conversion efficiency inside a foamtarget.
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