Energy redistribution between layers in multi-layered target heated by x-ray pulse

Multi-layered systems with alternated layers of different materials (laminates) with thickness of the order of tens nanometers are widely used in modern technologies, e.g., as x-ray mirrors. It is important to study effect of the x-ray free electron lasers on such targets. Highenergy photons penetrate deeply into material with an attenuation depth much larger than the thickness of a single layer of a laminate. Modern hard x-rays lasers may be focused to tiny focal spots in the direction approaching diffraction limit: record today is ≈ 50 nm; ∼ 1 μm diameters are now rather easily achieved. These lasers may be used for machining of laminates. We show that thermal evolution of illuminated laminates depends on not only photon absorption in the individual materials, but also on fast redistribution of absorbed energy within a nonequilibrium stage connected with electron–ion relaxation (two-temperature stage) between hot electrons heated by absorption and much colder ions. Because of the high heat conductivity of metal layers, especially at the two-temperature stage, energy redistribution must be considered with taking into account the energy transfer from electrons to ions with different electron–ion coupling parameters α for different metals. Thus, a higher energy can be localized in a material with higher α rather than in a material with higher photon absorption coefficient. (paper)