X-Ray Emission from Rare Gas Clusters in Intense Laser Fields

Abstract

Recent experimental observations have demonstrated, that the interaction of intense laser light with rare gas clusters leads to extremely energetic states of matter. For example, Xe(M) and Kr(L) shell transition photons with energies of up to 5 keV have been reported by McPherson et al.¹. Furthermore, highly charged (>30+) xenon ions with startup energies reaching 1 MeV have been observed by Ditmire et al.², using irradiation intensities of 10¹⁶ W/cm². Earlier, Snyder et al.³ were able to resolve xenon charge states as high as q=20 using a reflectron type time of flight mass spectrometer and laser intensities of about 10¹⁵ W/cm². The very effective energy transfer of the laser light into highly ionized atomic states embedded in clusters is currently interpreted as a result of small scale collective effects like coherent electron motion⁴⁵, ionization ignition⁶ or collisional absorption into cluster-sized nano-plasmas^2,7. To shed more light onto the ongoing discussion concerning the primary heating and ionization mechanism, e.g. the absorption of the laser light and the production of highly charged ion states, We present here a quantitative study on the x-ray yield as well as a function of the laser intensity (up to 10¹⁷ W/cm²), the target material (argon, krypton, xenon) and the cluster size (up to 2×10⁶). Our results contain also relevant data for possible future applications of clusters in strong fields as a renewable and very small x-ray source.