Nature 564, 91–94 (2018)

Inhomogeneous gas jets rather than solids may provide an answer to the tricky question of how to make refractive optical elements that operate in the extreme-ultraviolet (XUV) region. Unlike the visible and infrared regions where glass and plastic elements can be used to manipulate light beams, in the EUV region the strong absorption of most materials prevents this from being feasible. Now, a team of scientists from the Max-Born-Institut in Berlin, Germany have shown that helium and argon gas jets with a graded density profile can be used to make prisms and lenses for XUV light. The precise value of the deflection angle of a gas prism or the focal length of a gas lens can be controlled by the pressure of the gas jet, with increasing pressure yielding a stronger element, and the team demonstrates focal spots as small as a few tens of micrometres. Furthermore, as the gas is constantly replenished these XUV elements are immune to laser-induced damage.