Development of a collimated keV X-ray beam for probing of dense plasmas

Abstract : Experimental findings of a fully optical, keV x-ray source of 1-2° divergence and broadband spectrum (>5 keV bandwidth) are presented. The radiation results from the highly relativistic interaction of a 30 TW(1 J, 30 fs) laser pulse thru a 3 mm length span of He gas (ne = 1 x 10^19 electrons/cm^3). Quantitative measurements from the filtered back-illuminated CCD give 105 photons/eV, and the knife-edge technique measures the source diameter of 10 μm. These source characteristics, the measured beam of relativistic electrons, and PIC simulation indicate the radiation results from forceful transverse oscillations of the laser-accelerated electrons in response to the ionic channel formed by the laser pulse. The source brightness (10^7 photons/eV/mm^2m^2/shot and ultrafast duration (≤30 fs) make it applicable to both backlighting and x-ray science applications.