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Nature Physics 5, 693–696 (1 September 2009) | doi:10.1038/nphys1341

Turning solid aluminium transparent by intense soft X-ray photoionization

Bob Nagler , Ulf Zastrau , Roland R. F|[auml]|ustlin , Sam M. Vinko , Thomas Whitcher , A. J. Nelson , Ryszard Sobierajski , Jacek Krzywinski , Jaromir Chalupsky , Elsa Abreu , Sa|[scaron]|a Bajt , Thomas Bornath , Tomas Burian , Henry Chapman , Jaroslav Cihelka , Tilo D|[ouml]|ppner , Stefan D|[uuml]|sterer , Thomas Dzelzainis , Marta Fajardo , Eckhart F|[ouml]|rster , Carsten Fortmann , Eric Galtier , Siegfried H. Glenzer , Sebastian G|[ouml]|de , Gianluca Gregori , Vera Hajkova , Phil Heimann , Libor Juha , Marek Jurek , Fida Y. Khattak , Ali Reza Khorsand , Dorota Klinger , Michaela Kozlova , Tim Laarmann , Hae Ja Lee , Richard W. Lee , Karl-Heinz Meiwes-Broer , Pascal Mercere , William J. Murphy , Andreas Przystawik , Ronald Redmer , Heidi Reinholz , David Riley , Gerd R|[ouml]|pke , Frank Rosmej , Karel Saksl , Romain Schott , Robert Thiele , Josef Tiggesb|[auml]|umker , Sven Toleikis , Thomas Tschentscher , Ingo Uschmann , Hubert J. Vollmer , Justin S. Wark , Bob Nagler , Ulf Zastrau , Roland R. F|[auml]|ustlin , Sam M. Vinko , Thomas Whitcher , A. J. Nelson , Ryszard Sobierajski , Jacek Krzywinski , Jaromir Chalupsky , Elsa Abreu , Sa|[scaron]|a Bajt , Thomas Bornath , Tomas Burian , Henry Chapman , Jaroslav Cihelka , Tilo D|[ouml]|ppner , Stefan D|[uuml]|sterer , Thomas Dzelzainis , Marta Fajardo , Eckhart F|[ouml]|rster , Carsten Fortmann , Eric Galtier , Siegfried H. Glenzer , Sebastian G|[ouml]|de , Gianluca Gregori , Vera Hajkova , Phil Heimann , Libor Juha , Marek Jurek , Fida Y. Khattak , Ali Reza Khorsand , Dorota Klinger , Michaela Kozlova , Tim Laarmann , Hae Ja Lee , Richard W. Lee , Karl-Heinz Meiwes-Broer , Pascal Mercere , William J. Murphy , Andreas Przystawik , Ronald Redmer , Heidi Reinholz , David Riley , Gerd R|[ouml]|pke , Frank Rosmej , Karel Saksl , Romain Schott , Robert Thiele , Josef Tiggesb|[auml]|umker , Sven Toleikis , Thomas Tschentscher , Ingo Uschmann , Hubert J. Vollmer & Justin S. Wark

Saturable absorption is a phenomenon readily seen in the optical and infrared wavelengths. It has never been observed in core-electron transitions owing to the short lifetime of the excited states involved and the high intensities of the soft X-rays needed. We report saturable absorption of an L-shell transition in aluminium using record intensities over 1016|[thinsp]|W|[thinsp]|cm|[minus]|2 at a photon energy of 92|[thinsp]|eV. From a consideration of the relevant timescales, we infer that immediately after the X-rays have passed, the sample is in an exotic state where all of the aluminium atoms have an L-shell hole, and the valence band has approximately a 9|[thinsp]|eV temperature, whereas the atoms are still on their crystallographic positions. Subsequently, Auger decay heats the material to the warm dense matter regime, at around 25|[thinsp]|eV temperatures. The method is an ideal candidate to study homogeneous warm dense matter, highly relevant to planetary science, astrophysics and inertial confinement fusion.