Ultrafast opto-optical control of extreme ultraviolet light pulses
Sammanfattning: Extreme ultraviolet (XUV) light is a valuable frequency range for ultrafast optics experiments. The short wavelength is a requirement for ultrashort pulses, which are widely used to characterize fast dynamics. Additionally, the high photon energy enables quantum control of high frequency transitions in atoms. These transitions are of interest for ultrafast quantum control as the bandwidth of the control pulses needs to be less than the transition frequency. Presently, however, no good modulators exist for these frequencies, which significantly reduces the possible ultrafast optics experiments or applications in the XUV regime. This thesis addresses this problem and focuses on the control of XUV light in time and space. To enable control of XUV light a method is described which modulates the phase of XUV light emitted from a gas of noble atoms. The atoms are resonantly excited with a coherent XUV pulse generated through high order harmonic generation. After the excitation pulse has passed through the gas, the atoms will emit light in the absence of an external field, known as free induction. The phase of the emitted light is changed by shifting the resonance frequencies through the AC Stark shift with a non-resonant infrared control pulse. This phase-control of the emitting atoms also translates into a control of the phase of the emitted XUV field.With the method described in the previous paragraph, the direction of XUV light emitted from noble gases was controlled, and the temporal dynamics of the emission was studied. The redirection of the XUV emission, through the use of a spatially offset IR pulse, was found to change both with intensity of the control pulse and by changing the spatial offset between the pulses. By varying the delay between the excitation and the control pulse the time of redirection was controlled, which enabled high signal to noise study of the temporal dynamics of the emission. Furthermore, with two control pulses the emission was redirected twice, resulting in an XUV pulse shape with controlled duration emitted with a certain angle. Hopefully the presented work will result in more research into the development of this technique, to fully realize the possibility to shape the amplitude and phase of XUV pulses. Such a development would open the door for ultrafast XUV quantum control.
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