High-order harmonic generation using quantum dots

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Femtosecond laser pulses enable the production of coherent XUV radiation via the process of high harmonic generation. While in continuous gas targets this is an established process, we want to investigate spatially structured plasmas and quantum dots as target materials at laser repetition rates of 1 kHz. The spatially structured target allows to increase the interaction length between the target material and the fundamental driving radiation. Usually this leads to an increased phase mismatch and eventually destructive interference between the fundamental and the generated XUV radiation. The spatial structuring allows in principle to suppress the harmonic generation with the opposite phase and via quasi-phase matching an increased XUV photon yield is expected. Parameters influencing the harmonic phase evolution in and between the individual plasmas will be studied. Further, the response of the individual emitters might be increased. A promising approach in achieving this is to switch from single atoms or ions to clusters of atoms as conversion media. Their increased extend is thought to increase the recombination probability of the returning electron which emits the harmonic field. Very small clusters - quantum dots - with a diameter of a few nm are expected to give best results, because in addition they show sharp electronic resonances. At the end a combination of both approaches, quantum dots in structured plasmas, will be studied.