Strong field laser photoionization of β-estradiol in the 1013-1015 W/cm2 intensity range at wavelengths between 1200 and 2000 nm was examined for both evaporated gas phase molecules and neutral species sputtered from a solid surface under bombardment with 20 keV C60+ ions. It is shown that the ionization efficiency is saturated at laser intensities of the order of 1013 W/cm2, while laser-induced photofragmentation is found to strongly increase between 1013 and 1014 W/cm2 and stay constant at higher intensities. These findings suggest a strategy to improve the postionization efficiency by defocusing the laser beam in order to sample a larger fraction of the sputtered plume, while at the same time optimizing the conditions for intact photoionization of the sputtered molecules. The results reveal a substantial enhancement of the signal of intact postionized molecular ions to a level an order of magnitude above that of the corresponding secondary ions. They also provide an experimental estimate of ∼2.5 × 10-2 as an upper bound for the ion fraction (secondary ion formation probability) of the sputtered molecules. (Figure Presented).
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films