Multiply Charged Ions Formed by Multiphoton Absorption Processes in the Continuum

Abstract

Singly, doubly, triply, and quadruply charged krypton ions are formed by multiphoton absorption processes in krypton atoms. They are induced by a 50-psec laser pulse at 1.064 \ensuremath{\mu}m in the ${10}^{13}$-${10}^{14}$-W-${\mathrm{cm}}^{\ensuremath{-}2}$ intensity range. The percentage ratio between the numbers of doubly and singly ionized Kr atoms is 10% at 8\ifmmode\times\else\texttimes\fi{}${10}^{13}$ W ${\mathrm{cm}}^{\ensuremath{-}2}$. It is shown that ${\mathrm{Kr}}^{2+}$ ions result from a direct 33-photon absorption process. At 1.5\ifmmode\times\else\texttimes\fi{}${10}^{13}$ W ${\mathrm{cm}}^{\ensuremath{-}2}$, the 33-photon absorption rate is only about 60 times less than the 13-photon absorption rate which gives singly charged ions.