Generation and applications of cascaded coherent sources of extreme ultraviolet

This dissertation reports the generation and applications of coherent extreme ultraviolet (XUV) sources. By using a long gas cell and multiple colour collinear femtosecond laser fields, we have observed for the first time phase-matched cascaded four-wave mixing processes in the XUV region. We apply these bright light sources in studies of the dynamics of the atomic gases, the extension of the high harmonic generation cutoff region, and the generation of XUV quasi-continuum spectrum. We also investigate the effects of a weak near infrared control field on the propagation of the XUV radiation when two commensurate fundamental lasers are used.