The increasing availability of extremely high power lasers, both in average power up to hundreds of kilowatts and in peak power up to tens of terawatts, is raising the important question of beam manipulation. Conventional lenses—transparent solid dielectric materials—are subject to thermal stresses and laser-driven ionization, both leading to irreversible damage. The work of Johnson et al. presents simulations of a gas-based lens, where a controlled nitrogen flow is injected from the side into a confined structure, causing rapid gas rotation—a flow vortex—leading to a density reduction on axis. This forms a negative lens that would be relatively immune to both thermal and ionization effects, and whose focal length is varied by adjusting the mass flow rate.

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