Marija Kotur

Spectral phase measurement of a Fano resonance using tunable attosecond pulses.

Electron dynamics induced by resonant absorption of light is of fundamental importance in nature and has been the subject of countless studies in many scientific areas. Above the ionization threshold of atomic or molecular systems, the presence of discrete states leads to autoionization, which is an interference between two quantum paths: direct ionization and excitation of the discrete state coupled to the continuum. Traditionally studied with synchrotron radiation, the probability for autoionization exhibits a universal Fano intensity profile as a function of excitation energy. However, without additional phase information, the full temporal dynamics cannot be recovered. Here we use tunable attosecond pulses combined with weak infrared radiation in an interferometric setup to measure not only the intensity but also the phase variation of the photoionization amplitude across an autoionization resonance in argon. The phase variation can be used as a fingerprint of the interactions between the discrete state and the ionization continua, indicating a new route towards monitoring electron correlations in time.

Gating attosecond pulses in a noncollinear geometry

The efficient generation of isolated attosecond pulses (IAPs), giving access to ultrafast electron dynamics in various systems, is a key challenge in attosecond science. IAPs can be produced by confining the extreme ultraviolet emission generated by an intense laser pulse to a single field half-cycle or, as shown recently, by employing angular streaking methods. Here, we experimentally demonstrate the angular streaking of attosecond pulse trains in a noncollinear geometry, leading to the emission of angularly separated IAPs. The noncollinear geometry simplifies the separation of the fundamental laser field and the generated pulses, making this scheme promising for intracavity attosecond pulse generation, thus opening new possibilities for high-repetition-rate attosecond sources.

Measurements of relative photoemission time delays in noble gas atoms

We determine relative photoemission time delays between valence electrons in different noble gas atoms (Ar, Ne and He) in an energy range between 31 and 37 eV. The atoms are ionized by an attosecond pulse train synchronized with an infrared laser field and the delays are measured using an interferometric technique. We compare our results with calculations using the random phase approximation with exchange and multi-configurational Hartree-Fock. We also investigate the influence of the different ionization angular channels.

Spatiotemporal characterization of ultrashort laser pulses using spatially resolved Fourier transform spectrometry

We present a method for characterizing ultrashort laser pulses in space and time, based on spatially resolved Fourier transform spectrometry. An unknown pulse is interfered with a delayed, spatially uniform reference on a CCD camera. The reference pulse is created by spatially filtering a portion of the unknown pulse. By scanning the delay between the two pulses, an interferogram is obtained at each pixel, allowing us to determine the spatially resolved phase difference between the unknown pulse and the reference pulse. High-resolution spatiotemporal characterization of an ultrashort pulse is demonstrated, and the sensitivity of the method to spatiotemporal coupling is shown for the case of a pulse with pulse front tilt.

Attosecond pulse walk-off in high-order harmonic generation

We study the influence of the generation conditions on the group delay of attosecond pulses in high-order harmonic generation in gases. The group delay relative to the fundamental field is found to decrease with increasing gas pressure in the generation cell, reflecting a temporal walk-off due to the dispersive properties of the nonlinear medium. This effect is well reproduced using an on-axis phase-matching model of high-order harmonic generation in an absorbing gas.

Spatiotemporal characterization of ultrashort optical vortex pulses

We use a spiral phase plate to generate few-cycle optical vortices from an ultrafast titanium:sapphire oscillator and characterize them in the spatiotemporal domain with a recently introduced technique based on spatially resolved Fourier transform spectrometry. The performance of this simple approach to the generation of optical vortices is analysed from a wavelength-dependent perspective as well as in the spatiotemporal domain, allowing us to characterize ultrashort vortex pulses in space, frequency and time.

Phase Measurement of a Fano Resonance Using Tunable Attosecond Pulses

We study photoionization of argon atoms close to the 3s(2)3p(6) -> 3s(1)3p(6)4p Fano resonance using an attosecond pulse train and a weak infrared probe field. An interferometric technique combined with tunable attosecond pulses allows us to determine the phase of the photoionization amplitude as a function of photon energy. We interpret the experimental results using an analytical two-photon model based on the Fano formalism and obtain quantitative agreement.

FemtoMAX – an X-ray beamline for structural dynamics at the short-pulse facility of MAX IV

The FemtoMAX beamline facilitates studies of the structural dynamics of materials on the femtosecond timescale. The first commissioning results are presented.

Photoionization time delay measurement close to a Fano resonance using tunable attosecond pulses

We investigate the influence of a Fano resonance on the delays for electron emission in two-photon, near-resonant ionization of argon. The delays were measured using an interferometric method that employed an attosecond pulse train.

Stabilized interferometric attosecond timing measurements

We perform interferometric attosecond timing measurements to study XUV photo-ionization in noble gases, to diagnose macroscopic phase-matching conditions in high-order harmonic generation, and to investigate single-photon double-ionization by detecting electron pairs in coincidence.