Electron quantum path interferences in strongly laser driven aligned molecules and generation of circularly polarized XUVpulses

The aim of the thesis is to unravel the dynamics of the High Harmonic Generation (HHG) process induced in strongly laser driven aligned molecules and develop a method for the production of circularly polarized ultrashort pulses in the extreme-ultraviolet (XUV) spectral range. Towards these goals we have used the Time Gated Ion Microscopy (IM) technique and a pump-probe arrangement. The former maps the spatial XUV intensity distribution onto a spatial ion distribution (produced in the XUV focal area through a single–XUV– photon ionization process of an atomic gas). The pump–probe arrangement was used to trigger the molecular alignment process and generate the high–harmonics. Initially, in order to calibrate the harmonic generation/detection scheme, we have used only the IM and Argon (Ar) atoms for the generation of high-harmonics. In this experiment we have measured and quantified the influence of spatiotemporal coupling effects in HHG region. After, using N2 molecules and the IM approach in combination with the pump-probe arrangement, we have spatially resolved the interference pattern produced by the spatiotemporal overlap of the harmonics emitted by the short– and long–electron quantum paths, and we have succeeded in measuring in-situ their phase difference and disclose their dependence on molecular alignment. The findings constitute a vital step towards understanding of strong-field molecular physics and the development of a self-referenced attosecond spectroscopy approach. Additionally using the same pump-probe arrangement we demonstrate a method for the generation of circularly polarized XUV radiation using CO2 molecules, a matter which is important for investigating phenomena such as circular dichroism, ultrafast spin dynamics, magnetic microscopy, chirality assignment e.t.c.Στην παρούσα διδακτορική διατριβή, χρησιμοποιώντας την απεικονιστική μέθοδο του μικροσκοπίου ιόντων χρονικής πύλης (Time Gated Ion Microscopy), μελετήθηκε η διαδικασία της παραγωγής των αρμονικών στην περιοχή της παραγωγής τους. Η μελέτη πραγματοποιήθηκε για αρμονικές που παράγονται από την αλληλεπίδραση ισχυρών IR παλμών λέιζερ με άτομα (Ar) και ευθυγραμμισμένα μόρια αζώτου (N2). Η ευθυγράμμιση των μορίων επιτεύχθηκε με την ανάπτυξη μίας διάταξης άντλησης-ανίχνευσης (pump-probe). Η καταγραφή της χωρικής κατανομής της έντασης των αρμονικών στην περιοχή της παραγωγής τους οδήγησε σε σημαντικά συμπεράσματα τόσο για την εξάρτηση της διαδικασίας παραγωγής των αρμονικών από την σχετική θέση του jet παραγωγής και της δέσμης του IR στην περιοχή της παραγωγής των αρμονικών, όσο και για την δυναμική της ευθυγράμμισης των μορίων. Η ίδια διάταξη χρησιμοποιήθηκε για την παραγωγή XUV ακτινοβολίας με υψηλό βαθμό ελλειπτικότητας από ευθυγραμμισμένα μόρια διοξειδίου του άνθρακα (CO2)

Generation of Attosecond Light Pulses from Gas and Solid State Media

Real-time observation of ultrafast dynamics in the microcosm is a fundamental approach for understanding the internal evolution of physical, chemical and biological systems. Tools for tracing such dynamics are flashes of light with duration comparable to or shorter than the characteristic evolution times of the system under investigation. While femtosecond (fs) pulses are successfully used to investigate vibrational dynamics in molecular systems, real time observation of electron motion in all states of matter requires temporal resolution in the attosecond (1 attosecond (asec) = 10−18 s) time scale. During the last decades, continuous efforts in ultra-short pulse engineering led to the development of table-top sources which can produce asec pulses. These pulses have been synthesized by using broadband coherent radiation in the extreme ultraviolet (XUV) spectral region generated by the interaction of matter with intense fs pulses. Here, we will review asec pulses generated by the interaction of gas phase media and solid surfaces with intense fs IR laser fields. After a brief overview of the fundamental process underlying the XUV emission form these media, we will review the current technology, specifications and the ongoing developments of such asec sources