Resonant multiphoton ionization of neon. Experimental determination of the polarizability of the3p′[12]1level

Abstract

Multiphoton ionization of neon in the case of a 16-photon resonance with the $3p^{\prime }{\left[\frac{1}{2}\right]}_1$ intermediate level is studied using a neodymium-glass laser. Experiments show that when the electric field $E$ ranges from 2.2 × ${10}^7$ to 3.5 × ${10}^7$ V/cm, the number of collected charges takes a maximum value at 2.9 × ${10}^7$ V/cm. A theoretical study on the basis of the formalisms due to Keldysh and Zon etal predicts that, when an intermediate resonant level is considered, this maximum can be observed by the use of a laser beam of sufficiently large spectral width. This is the case in our experiment. The number of ionization events decreases when the resonance is destroyed, i.e., when the Stark shift of the level becomes larger than the spectral width of the laser, which, at 16 photons, is of the order of 100 Å. Good agreement between experiment and theory allows us to determine the polarizability of the resonant $3p^{\prime }{\left[\frac{1}{2}\right]}_1$ level of neon which is found to be 21.8 ${\mathrm{\AA }}^3$. We have also determined an experimental cross section of multiphoton ionization of neon at $\lambda =1.06\mathrm{}$ μm.