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

Experimental findings of a fully optical, keV x-ray source of 1-2 degrees 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 through a 3 mm length span of He gas (ne = 1*1019 electrons/cm3). Quantitative measurements from the filtered back-illuminated CCD give 105 protons/eV, and the knife-edge technique measures the source diameter of 10 μm. These source characteristics, the measured beam of relativistic electrons, and PIC (particle-in-cell) 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 (107 photons/eV/mm2/mr2/shot and ultra-fast duration (≤ 30 fs) make it applicable to both back-lighting and X-ray science applications. (authors)