Non-thermal desorption/ablation of molecular solids induced by ultra-short soft x-ray pulses

Abstract

Abstract: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. 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. A model describing non-thermal desorption and ablation has been developed and used to analyze single-shot imprints in PMMA. An intermediate regime of materials removal has been found, confirming model predictions. We also report below-threshold multiple-shot desorption of PMMA induced by high-order harmonics (HOH) at 32nm. 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. B. Rus, A. Carillon, P. Dhez, P. Jaeglé, G. Jamelot, A. Klisnick, M. Nantel, and P. Zeitoun, "An efficient, high-brightness soft X-ray laser at 21.2 nm," Phys. Rev. A55, 3858-3873 (1997 S. Heinbuch, M. Grisham, D. Martz, and J. J. Rocca, "Demonstration of a desk-top size high repetition rate soft x-ray laser," Opt. Express 13, 4050-4055 (2005). 10. P. E. Dyer, "Excimer laser polymer ablation: twenty years on," Appl. Phys. A77, 167-173 (2003), and references cited therein. 11. L. V. Zhigilei, B. J. Garrison, "Molecular dynamics simulation study of the fluence dependence of particle yield and plume composition in laser desorption and ablation of organic solids," Appl. Phys. Lett. 74, 1341-1343 (1999)

Saturated ablation in metal hydrides and acceleration of protons and deuterons to keV energies with a soft-x-ray laser

“…Nonthermal melting and ablation occur on timescales faster than conventional melting, an idea supported by earlier damage studies done at FLASH [4]. We define the critical charge density as the point where the density of free carriers (N ) is high enough to destabilize the lattice.…”

“…Breakthrough results have been reported in coherent diffractive imaging [1], femtosecond x-ray holography [2], cluster physics [3], and high-energy density science [4,5]. Parallel developments with table-top x-ray lasers demonstrate new capabilities at a significantly smaller laboratory scale [6][7][8][9].…”

“…The resulting plasma can reach very high temperatures, and in the present experiments 400 eV (4.6 million K) has been reached. The plasma expands over a couple of picoseconds and ends in the vaporization of micron-sized objects [2] or in the ablation of bulk solids (within a few nanoseconds) [4]. Resolidification of the surface layer in solids requires an additional 100 ns [20].…”

Desorption/ablation of lithium fluoride induced by extreme ultraviolet laser radiation

“…Following the analysis of ablation/desorption craters in molecular solids irradiated by the short pulses of XUV free-electron laser [10], it was recognized that desorption is at least one order of magnitude more effi cient for soft X-rays than for UV-Vis laser light. Therefore, the above mentioned Haglund's criterion was reconsidered and phenomenological model describing nonthermal desorption/ablation was proposed in Ref.…”

“…Therefore, the above mentioned Haglund's criterion was reconsidered and phenomenological model describing nonthermal desorption/ablation was proposed in Ref. [10]. The depth of crater in desorption region is defi ned by this model as being linearly proportional to: (i) attenuation length (l att ); (ii) the ratio of incident laser fl uence (F) and the laser ablation threshold fl uence (F th ), and fi nally (iii) effi ciency of desorption ( des ).…”