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Mathematical Description of Plasmonic Enhancements in High Harmonic Generation

Students from Newham Collegiate Sixth Form, Dr Abbie Bray and Dr Cornelia Hofmann

In this work, we study High Harmonic Generation, a process by which an electron is ejected from its parent ion by a strong laser field in the infrared (IR) range, accelerating under the influence of the same field, and in a third and final step recombining again. Since the electron gains a lot of energy in this process, when it recombines it releases a high-energy XUV photon. Thus, this process converts IR laser pulses in to ultrashort XUV pulses. We have used maths to investigate what happens when an additional nanostructure modifies the shape and strength of the incoming laser field, thereby altering the path that the electrons take, changing their energy at recombination, and changing there combination probability in the first place. For this purpose, we have compared data resulting from two different mathematical descriptions of the spatial dependence in the laser field, one based on a linear approximation which is commonly used for similar studies, and one aiming to describe the physical characteristic of the field more accurately. We have found significant differences between the two models, suggesting that there are limitations to the linear approximation

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