-Collective effects in High density regime.

· Laser ablation in solid targets

o Cluster formation

o Mass analysis of yields

· Multiphoton ionization in gas jet

o Collective effects in high density regime

o Ion acceleration

-Anomalous Saturation of Ion yields vs Laser Intensity due to electron-ion trapping at various gas density in Ar.

Curves correspond to different gas densities given in millibar.

-In the absence of electron-ion interactions, curves should be parallel and linearly dependent on the gas density as it occurs at a signal <=1 mV.

-The electron-ion trapping, which depends on the absolute charge density produced by laser, screens the external electric field and prevent ions from collection. It leads to an “apparent” saturation of the signal that does not corresponds to the saturation of ionization.

-Mutual interactions among ion clouds.

³⁶Ar and ⁴⁰Ar

§ Due to interaction by repulsive electrostatic forces the cloud containing a lighter isotope accelerates (-134 ns), while the cloud with the heavier isotope slows

(+198 ns).

§ By increasing the ion density the difference in the time of arrival increases due to the growing mutual repulsion between clouds but the ion signals do not overlap.

§ This effect can be exploited to enhance the isotope separation in high gas density regime.

REFERENCES