<title>Generation of intense ultrashort x-ray pulses</title>

Abstract

Modeling of x-ray emission from targets heated by an ultrashort-pulse high-intensity optical laser is discussed. One application, using the emitted x rays, is pumping inner-shell photo-ionized x-ray lasers. Short wavelength lasing ({lambda} {le} 15 {Angstrom}) requires fast rise-time 1--3 key x rays to ionize inner K-shell electrons. It has been shown that structured targets, consisting of grooves on a solid material or a composite of clusters, have high absorption. We model grooved targets as an ensemble of exploding foils finding that the rise time of x rays is rapid enough for pumping inner-shell x-ray lasers. We show that simple atomic models can overestimate the energy in x-ray emission bands. High-Z materials are found to have the highest conversion efficiency but mid-Z materials can be used to provide a band of emission at a particular energy. We show that the pondermotive inhibition of expansion has only a small effect on the x-ray emission. The emission of a Au plasma is found to be appropriate for pumping inner-shell lasing at 14.6 {Angstrom} in Ne. The required optical laser intensity is of order 10{sup 17} W/cm{sup 2} using a 100 fsec FWHM duration pulse. To produce a laser with a gain-length product of order 10 requires 5--15 J of optical energy.