Femtosecond laser micromachining of glass chips for high-order harmonic generation

Since the first observation of High-order Harmonic Generation (HHG) in gas twenty years ago, the combination of intense research together with technological developments, has led to impressive progress in the field of extreme ultraviolet spectroscopy and attosecond science. Beam lines based on HHG extend over several meters and are based on instrumentation that requires careful alignment and even active stabilization systems. Therefore, a miniaturization of HHG beams will reduce the cost of these light sources and pave the way to their application in numerous new fields. Femtosecond laser micromachining followed by chemical etching (FLICE) has already demonstrated its high potential in the fabrication of fused silica lab-on-a-chip devices; it can directly produce microfluidic networks in a 3D geometry directly buried in the glass substrate. Until now, they have been extensively used for the manipulation of fluids but they are perfectly suitable for the manipulation of gas as well. In this work, we will demonstrate HHG in a gas filled microchannel network fabricated by the FLICE technique. The device structure will be based on hollow waveguides: several inlets will deliver the gas into a central hollow waveguide where the ultrafast laser will be coupled and HHG will take place. The high versatility of the FLICE technique will allow us to fabricate devices with modulated gas concentration and waveguide profile to achieve quasi-phase-matching conditions. Moreover, we will also demonstrate an integrated filtering chip that will allow to geometrically separate the main laser radiation from the XUV generated beam.