In this talk, I will present our recent developments in the UDynI group (www.udyni.eu).

High Harmonic Generation (HHG), arising from the interaction of intense femtosecond laser pulses with noble gases, led to the realization of table-top sources of coherent Extreme UltraViolet (EUV) and Soft-X Ray radiation. As a result, ultrafast spectroscopy can nowadays be performed with extreme temporal resolutions, down to the attosecond regime, and site and chemical selectivity. These peculiar features grant access to purely electronic dynamics in molecules and solids, initiated by ultrafast laser pulses, and to fundamental light-matter interaction processes. One of the most promising all-optical techniques to perform these experiments is transient absorption in the XUV. However, the full exploitation of ultrafast spectroscopy in this spectral range is somehow hindered, even today, by the technological complexity of the required setups and the low generation efficiency of the HHG sources, particularly when moving toward higher photon energies. We recently demonstrated efficient XUV generation inside a microfluidic device fabricated by femtosecond laser irradiation followed by chemical etching. This microfluidic approach allowed us to control and manipulate the harmonic generation conditions in gas on the micrometer scale with unprecedented flexibility, enabling a high photon flux and phasematching on broadband harmonics up to 200 eV. We further developed this approach, by implementing filters for the separation of the HHG field from the driving field.

Furthermore, HHG has been successfully used as a spectroscopic tool in condensed matter, allowing all-optical band structure reconstruction and Berry phase retrieval, demonstrating the flexibility and potentiality of this technique. In this framework, the polarization state of the harmonic field can be used to access further information about the symmetry of the sample under investigation and the physics involved during the HHG process. We implemented a pump-probe setup for the study of semiconductors and I will show here preliminary results.