An Intense Attosecond Light Source - from Generation to Application
Sammanfattning: Short and intense XUV pulses are important tools to study ultrafast dynamics and non-linear processes in matter. These pulses can be generated by free electron lasers (FELs) or by high-order harmonic generation (HHG), which are two complementary techniques. The advantage of HHG is the possibility to generate pulses with durations on the attosecond timescale, but the low conversion efficiency of the process makes it difficult to achieve pulses sufficiently intense for non-linear ionization. In HHG an infrared (IR) laser pulse is focused into a gas and new, higher frequencies in the extreme ultraviolet (XUV) regime are generated. To achieve intense XUV light, many photons must be generated and subsequently focused tightly in the experiment. This thesis describes the build-up of the Intense XUV Beamline in Lund and development of spectrometers used to study the charged fragments resulting from the non-linear ionization. An energetic and low repetition rate laser is used, and by focusing the pulse using a long focal length lens, the optimum intensity for HHG can be achieved in a large volume of gas. The XUV beam is tightly focused in the experiment using a short focal length mirror. Due to the low repetition rate in the experiment, a spectrometer that can record many events per shot was designed and constructed. The spectrometer is a double sided velocity map imaging spectrometer (DVMIS) that can record electrons and ions simultaneously. By using covariance techniques, correlations between fragments can be retrieved. The XUV pulses generated in the beamline are sufficiently intense to induce non-linear effects in matter and have been used to study two-photon double ionization of neon.
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