Attosecond XUV-IR pump-probe measurements of small molecules using 3D momentum spectroscopy

The thesis reports on experiments conducted at a beamline combining a high-order harmonic generation-based attosecond pulse source operating at 100 kHz with an electron-ion coincidence detector (Reaction Microscope). The beamline is driven by a noncollinear optical parametric chirped pulse amplification system, in which few-cycle near infrared pulses generated by a titanium sapphire oscillator are amplified using the picosecond laser pulses delivered by a ytterbium-YAG pump laser. The reported beamline is designed for extreme ultraviolet–near infrared pump-probe experiments either with attosecond pulse trains or isolated attosecond pulses. A series of time-resolved measurements with attosecond pulse trains were performed in molecular nitrogen focusing on the predissociative ionic C state. The corresponding ultrafast photoelectron dynamics was accessed with vibrational resolution. The performed investigation revealed a non-trivial energy dependence of extracted photoionization delays with respect to a noble gas reference. The observed effect could be a consequence of the multi-electron character of the photoinduced process under investigation. The reported results are manifesting one more step towards the attosecond spectroscopy of large complex molecules with coincidence detection

Retrieval of attosecond pulse ensembles from streaking experiments using mixed state time-domain ptychography

The electric field of attosecond laser pulses can be retrieved from laser-dressed photoionisation measurements, where electron wavepackets that result from single-photon ionisation by the attosecond pulse in the presence of a dressing field are produced. In case of fluctuating dressing laser and/or attosecond pulses, e.g. due to pulse-to-pulse fluctuations of the carrier envelope phase of the infrared laser pulse, commonly applied retrieval algorithms result in the erroneous extraction of the pulse fields. We present a mixed state time-domain ptychography algorithm for the retrieval of pulse ensembles from attosecond streaking experiments. © 2020 The Author(s). Published by IOP Publishing Ltd

Retrieval of attosecond pulse ensembles from streaking experiments using mixed state time-domain ptychography

The electric field of attosecond laser pulses can be retrieved from laser-dressed photoionisation measurements, where electron wavepackets that result from single-photon ionisation by the attosecond pulse in the presence of a dressing field are produced. In case of fluctuating dressing laser and/or attosecond pulses, e.g. due to pulse-to-pulse fluctuations of the carrier envelope phase of the infrared laser pulse, commonly applied retrieval algorithms result in the erroneous extraction of the pulse fields. We present a mixed state time-domain ptychography algorithm for the retrieval of pulse ensembles from attosecond streaking experiments

Generation and characterisation of few-pulse attosecond pulse trains at 100 kHz repetition rate

The development of attosecond pump-probe experiments at high repetition rate requires the development of novel attosecond sources maintaining a sufficient number of photons per pulse. We use 7 fs, 800 nm pulses from a non-collinear optical parametric chirped pulse amplification laser system to generate few-pulse attosecond pulse trains (APTs) with a flux of >106 photons per shot in the extreme ultraviolet at a repetition rate of 100 kHz. The pulse trains have been fully characterised by recording frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG-CRAB) traces with a velocity map imaging spectrometer. For the pulse retrieval from the FROG-CRAB trace a new ensemble retrieval algorithm has been employed that enables the reconstruction of the shape of the APTs in the presence of carrier envelope phase fluctuations of the few-cycle laser system. © 2020 The Author(s). Published by IOP Publishing Ltd

Generation and characterisation of few-pulse attosecond pulse trains at 100 kHz repetition rate

The development of attosecond pump–probe experiments at high repetition rate requires the development of novel attosecond sources maintaining a sufficient number of photons per pulse. We use 7 fs, 800 nm pulses from a non-collinear optical parametric chirped pulse amplification laser system to generate few-pulse attosecond pulse trains (APTs) with a flux of >106 photons per shot in the extreme ultraviolet at a repetition rate of 100 kHz. The pulse trains have been fully characterised by recording frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG-CRAB) traces with a velocity map imaging spectrometer. For the pulse retrieval from the FROG-CRAB trace a new ensemble retrieval algorithm has been employed that enables the reconstruction of the shape of the APTs in the presence of carrier envelope phase fluctuations of the few-cycle laser system

Generation and characterization of isolated attosecond pulses at 100 kHz repetition rate

The generation of coherent light pulses in the extreme ultraviolet (XUV) spectral region with attosecond pulse durations constitutes the foundation of the field of attosecond science. Twenty years after the first demonstration of isolated attosecond pulses, they continue to be a unique tool enabling the observation and control of electron dynamics in atoms, molecules, and solids. It has long been identified that an increase in the repetition rate of attosecond light sources is necessary for many applications in atomic and molecular physics, surface science, and imaging. Although high harmonic generation (HHG) at repetition rates exceeding 100 kHz, showing a continuum in the cutoff region of the XUV spectrum, was already demonstrated in 2013, the number of photons per pulse was insufficient to perform pulse characterization via attosecond streaking, let alone to perform a pump-probe experiment. Here we report on the generation and full characterization of XUV attosecond pulses via HHG driven by near-single-cycle pulses at a repetition rate of 100 kHz. The high number of 106 XUV photons per pulse on target enables attosecond electron streaking experiments through which the XUV pulses are determined to consist of a dominant single attosecond pulse. These results open the door for attosecond pump-probe spectroscopy studies at a repetition rate 1 or 2 orders of magnitude above current implementations