Femtosecond laser micromachining of integrated devices for XUV generation.

Extreme ultraviolet radiation (XUV, $10\mbox{--}124 {eV}$) is at the core of the most advanced technologies for the in-depth study of matter, but the need for huge and expensive facilities to generate such high-energies photons limits its availability to few laboratories around the world. We propose a new kind of approach, based on integrated photonic, to generate and manipulate XUV radiation in a few-centimeter platform, consisting of a network of empty channels embedded in a glass sample. To realize this platform, we push beyond the limits of an extremely versatile micromachining technique called Femtosecond Laser Irradiation followed by Chemical Etching, which allows the realization of a 3D hollow core structure inside transparent materials. We demonstrated that these structures can host the interaction between a noble gas and a femtosecond laser beam, triggering high-order harmonic generation which ends up in the delivery of ultrashort XUV pulses, with a conversion efficiency of up to $10^{-5}$ in the $40\mbox{--}50 {eV}$ spectral region. This result represents the basis for the future development of a miniaturized and a highly efficient XUV source.