Author(s): Roland Hergenröder, Ota Samek, Vanja Hommes

Abstract:

“Laser ablation mass spectrometry (LA-MS) has always been an interesting method for the elemental analysis of solid samples. Chemical analysis with a laser requires small amounts of material. Depending on the analytical detection system, subpicogram quantities may be sufficient. In addition, a focused laser beam permits the spatial characterization of heterogeneity in solid samples typically with micrometer resolution in terms of lateral and depth dimensions. With the advent of high-energy, ultra-short pulse lasers, new possibilities arise. The task of this review is to discuss the principle differences between the ablation process of short (>1 ps) and ultra-short (<1 ps) pulses. Based on the timescales and the energy balance of the process that underlies an ablation event, it will be shown that ultra-short pulses are less thermal and cause less collateral damages than longer pulses. The confinement of the pulse energy to the focal region guarantees a better spatial resolution in all dimensions and improves the analytical figures of merit (e.g., fractionation). Applications that demonstrate these features and that will be presented are in-depth profiling of multi-layer samples and the elemental analysis of biological materials.”

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Author(s): Ota Samek, Vanja Hommes, Roland Hergenröder, Sergei V. Kukhlevsky

Abstract:

“We report on a beam shaping technique for femtosecond laser pulses based on a liquid-crystal display. The system is capable of modifying femtosecond Gaussian beams to a flattop beam. A pattern projected onto liquid-crystal display modifies the incoming Gaussian beam intensity so that flattop intensity profile is obtained. The process is monitored online using a charge-coupled device camera so that the intensity distribution of each pulse is known. An experimental example of the depth profile of a Cr layer on a Si substrate obtained using such a modified beam is presented.”

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