Tabletop coherent XUV radiation sources.

摘要

Recent advances in short-pulse, high intensity laser systems have enabled the development of new, high repetition rate, tabletop-scale coherent extreme ultraviolet (XUV) radiation sources. Such sources, based on either XUV lasing transitions in a highly charged ion or on the generation of high-order harmonics of the driving laser wavelength, have potential application in such diverse areas of research as atomic physics, surface science, and molecular biology.; This dissertation documents two linked research efforts into laser-based XUV generation methods. The first was an investigation into the erratic output fluctuations that plagued the operation of the 41.8 nm XUV laser in Xe IX since its initial demonstration at Stanford in 1994. We report the fluctuations to result from the presence of a small prepulse in the output of the femtosecond-pulse high-intensity Ti:Sapphire driving laser used in our experiments. The detrimental effect of the prepulse on the gain of the Xe IX laser is experimentally demonstrated, and the mechanism of this effect is discussed in terms of a simple hydrodynamic model of a “pre-plasma” formed by the prepulse in the Xe IX laser gain region. We also experimentally demonstrate the benefit of an simple electro-optic switch as a means of reducing the prepulse to a level at which no pre-plasma is formed.; The second investigation was an outgrowth of an effort to obtain saturated output from the Xe IX laser by extending its gain length through waveguiding of the Ti:Sapphire driving laser. Ultimately, waveguide damage due to the high intensity driving laser pulses necessary for Xe IX formation precluded this application of waveguiding. However, the relatively lower driving laser intensities required for high-order harmonic generation enabled the use of the same waveguiding techniques to phasematch the high-order harmonic output. Following the initial demonstration of waveguide phasematching by Rundquist, et al., we report phasematching of the 25th harmonic of the 800 nm incident laser light under the new condition of multimode excitation of the waveguide. From these experiments we obtained confirmation of the original phasematching results along with previously unobserved phasematching effects associated with the multimode excitation. We use a simple model of mode interference to simulate the interactions within the waveguide and obtain a calculated XUV output which agrees well with our experimental observations.