Control of Coherent Extreme Ultraviolet Light and Light Sources

Abstract: Coherent extreme ultraviolet (XUV) light sources are necessary for the investigation of physical processes in the natural length and time scales of atoms. These experiments require a high degree of control of the coherent XUV light. The optical components and techniques, which are available for visible and infrared light, unfortunately cannot be used for controlling XUV light. In this thesis, novel techniques to control ultraviolet to XUV light are presented. The sources of XUV light discussed in this thesis include: high-order harmonic generation, free electron lasers and nitrogen air lasing. These sources are complementary and are suited for different applications.High-order harmonic generation produces XUV light with a very large spectral bandwidth, which can be compressed to produce the shortest light pulses to date. The yield of XUV light that can be produced through high-order harmonic generation is limited since the conversion efficiency of this process is low. Our experiments therefore aim to develop low-loss techniques for controlling the XUV light. We demonstrate techniques to measure and control the spatial phase of the harmonics using quantum path interference, and to control the XUV light after it is generated using opto-optical modulation.In contrast to high-order harmonic generation, free electron lasers can produce XUV pulses with very high intensities and at tunable wavelengths. Furthermore, there are free electron lasers where the amplitude and phase control of the XUV light, when compared to other sources, is unparalleled. The pulses that are produced with FELs, however, are not sufficiently short to perform attosecond ($1\cdot10^{-18}$s) experiments. In this thesis, we describe a free electron laser experiment, where sub-femtosecond waveform structures are generated in a controlled and reproducible way. The results from this experiment present the possibility to perform attosecond physics using free electron lasers, a field which was previously confined to the high-order harmonic generation community.Finally, experiments with nitrogen air lasing are also presented in this thesis. Unlike the other techniques, nitrogen air lasing does not produce XUV light. Instead, this technique produces coherent ultraviolet light, which is promising for atmospheric remote sensing. Since the mechanism generating the light with this technique is currently not understood, a recollision model, similar to the model describing high-order harmonics generation, is tested.None of the aforementioned sources have the same intensity, coherence or possibility to be controlled as conventional lasers. Instead, these sources excel within their own parameter space. Our experiments aim to push these techniques to cover the gaps where none of these sources currently can be used.