Stefanos Chatziathanasiou's research while affiliated with Foundation for Research and Technology - Hellas and other places

... This also shows that appropriate time and space resolved characterization and monitoring of such gas valves is an important aspect for its application and reproducible performance is easily achieved by properly managing the synchronization of gas jet with respect to the arrival time of the laser. The results are also important to a diverse field of studies which can benefit from high repetition rate gas jets, where the signature effects of the phenomena, have sensitive dependence upon the precise gas density profile such as molecular or atomic quantum path interferometry [68,69], ion spectroscopy from dilute plasma [70,71] spatio-temporal [72] and equivalently spatio-spectral [48,73] control of attosecond pulses, and in designing of gas based extreme-ultraviolet re-fractive optics [47], to name a few. ...

... agreement between experiments and numerical predictions is very good, indicating that the divergence increases with rising harmonic order for both gas targets under the present experimental conditions. Similar studies [34][35][36][37] investigating the spatial characteristics of high-order harmonic beams have reported the dependence of the XUV divergence (and focusing properties) on the longitudinal position of the generating medium and on the harmonic order. Such dependencies can be ascribed to the wavefront curvature of the IR-generating beam and that induced by the intensity-dependent dipole phase. ...

... In the HHG process, a fundamental frequency laser is converted into bursts of high-energy photons. Thus the obtained harmonics enable the generation of coherent extreme ultraviolet or soft X-ray light sources [11][12][13]. HHG is typically activated in atomic or molecular gases. ...

... In order to overcome these limitations, several approaches were suggested, including (i) the resonant enhancement of elliptically polarized harmonics [13,14], (ii) conversion of linearly polarized harmonics to elliptically polarized ones via phase-shifting optics [15,16], (iii) HHG from molecules, which often show a higher efficiency compared with atoms, especially for pump lasers with elliptical polarization [17,18], and can lead to efficient generation of elliptically polarized harmonics in the case of aligned molecules [19,20], as well as the use of (iv) cross-linearly-polarized two-color laser fields [21,22], and (v) bielliptic [23] or bicircular [24] fields, which have led to the demonstration of the first bright tabletop soft X-ray source for magnetic circular dichroism measurements [25]. However, neither of them allows for the generation of sub-femtosecond XUV pulses with sufficiently high energy, high ellipticity and a well defined polarization state common for the harmonics of different orders. ...