In the last decades, rapid development of soft x-ray and XUV lasers opened a relatively new area of the laser-matter interaction. Short-time exposure imprints provide sufficient information about transverse beam profile in HOH’s tight focus whereas long-time exposed PMMA exhibits radiation-initiated surface hardening making the beam profile measurement infeasible. We also report below-threshold multiple-shot desorption of PMMA induced by high-order harmonics (HOH) at 32nm. An intermediate regime of materials removal has been found, confirming model predictions. A model describing non-thermal desorption and ablation has been developed and used to analyze single-shot imprints in PMMA. Irradiated by the focused beam from the Free-electron LASer in Hamburg (FLASH) at 21.7nm, the samples have been investigated by atomic-force microscope (AFM) enabling the visualization of mild surface modifications caused by the desorption. We report the first observation of single-shot soft x-ray laser induced desorption occurring below the ablation threshold in a thin layer of poly (methyl methacrylate) - PMMA.
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