High-order Harmonic Generation

摘要: X-rays were observed for the first time by Wilhelm Conrad Rontgen in 1895 (Rontgen, 1895). During century since that great event benefiting mostly from their spatial resolution capability. However, recently it was possible to take advantage also temporal due novel sources providing ultrashort bursts of shortwavelength radiation (i.e. wavelength λ < 100 nm) and get an inside view physical processes molecules atoms. One possibility how obtain coherent extreme ultraviolet (abbreviated XUV or EUV; spectral range between 10-100 nm), soft X-ray (1-10 and/or (< 1 is high-order harmonic generation (HHG) process. It involves interaction laser light at a given frequency during which being converted into integer multiples fundamental through highly nonlinear with conversion medium (typically noble gas; Brabec & Krausz, 2000). Laser-driven HHG uses acceleration electrons on time-scales are order optical cycle field. Currently this technique gives rise shortest flashes ever generated laboratory typically few hundreds attoseconds (1 as = 10-18 s; Paul et al., 2001; Kienberger 2004; Schultze 2007). When field intensity about 1014 1015 W/cm2 durations