Creation of highly charged gold ion beam through collisional ionizations in a dense gold plasma driven by a femtosecond petawatt laser

Numerical investigations of the ionization mechanisms in the high-temperature high-density gold plasma formed by a high-contrast high-intensity laser pulse interacting with gold foil are performed to investigate high-efficiency gold ion acceleration with few petawatt (PW)-level laser systems, aiming at producing <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mo>≳</a:mo><a:mn>10</a:mn></a:mrow></a:math> MeV/u gold beams required to serve as an alternative to the front end of a conventional heavy-ion accelerator complex such as an ion source, linac, and drift tube linac. Short-pulse high-intensity laser pulses with a peak intensity of a few times <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:msup><b:mn>10</b:mn><b:mn>22</b:mn></b:msup><b:mspace width="4pt"/><b:msup><b:mi>Wcm</b:mi><b:mrow><b:mo>−</b:mo><b:mn>2</b:mn></b:mrow></b:msup></b:mrow></b:math>, which is not strong enough to expel Au L-shell electrons by laser field ionization, are shown to sufficiently resistively heat up the target bulk temperature so that collisional ionization by electrons in the plasma can expel L-shell electrons. The resultant highly charged Au ions (<d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:mo>∼</d:mo><d:mo>+</d:mo><d:mn>72</d:mn><d:mo>±</d:mo><d:mn>4</d:mn></d:mrow></d:math>) are exposed to the sheath field and accelerated to higher energies of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mo>∼</e:mo><e:mn>20</e:mn></e:mrow></e:math> MeV/u.