Erzeugung von Harmonischen durch Reflexion hochintensiver Laserpulse an einem ueberdichten Plasma

Abstract

The quest for a coherent source of extreme ultraviolet (XUV) and soft X-ray radiation has been underway for several years. In addition to basic physics research, such a source could lead to a variety of applications in X-ray microscopy and holography, biology and lithography. For high incident laser intensities frequency upconversion due to nonlinear processes in gaseous media is limited by ionisation defocussing and phase matching. With the advent of table-top terawatt laser systems a new route can be considered, the reflection of superintense laser pulses from an overdense plasma. In this case harmonic generation is expected to become more efficient with increasing laser intensity since the nonlinearity originates from relativistic effects. Up to now only one experiment using a CO_2 laser has been successful generating harmonics up to 46"t"h order and thus approaching the ultraviolet region. In this thesis harmonics of a high power, femtosecond Ti:sapphire laser were generated for the first time from an overdense plasma. The highest order obtained was 7"t"h in case of irradiation with the laser fundamental frequency, while the shortest wavelength at 99 nm was realized by the 4"t"h harmonic of frequency doubled irradiation. From the experimental results the physical mechanism could be inferred which is the reflection of ultraintense laser pulses off a steep plasma density gradient91 refs.Available from TIB Hannover: RN 5339(213) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman