Study of soft X-ray induced by plasma laser

X-ray radiation is generated by laser induced plasma also at very low laser fluence. In this work the diagnostic of a pulsed X-ray source utilizing as detector a very sensitive fast polarized Faraday cup is described. The plasma was generated by a pulsed KrF excimer laser focused on a pure copper target. The X-ray energy was studied at 30 and 102 mJ laser energy focused by a convergent lens of 15 cm focal length which provided an intensity of 1.3x108 and 4.5x108 Wcm-2, respectively. The maximum X-ray energy was approximately 1 keV for the both laser energies, whereas the energy peak value was of about 140 eV for the lower laser energy and about 160 eV for the higher. This behavior was compared with the calculation of plasma temperature performed by the Faraday cup at long time. The plasma temperature was determined by the best fit of the modified Maxwell-Boltzmann equation which resulted of about 600 kK (57 eV) and 970 kK (84 eV) for the lower and higher applied laser energy. Such a source is useful for studying on living cells and on sequencing of DNA