Generation of multiply charged tin and carbon ions in low intensity Coulomb explosion of tetramethyl tin clusters: Role of screening effects

• Charge state of atomic ions increases with laser wavelength.
• Screening effects result in lowering of ionization energy of cluster constituents.
• Extent of lowering of I.E. is dependent on charge state and atomic number of ion.
• Optimum number of charge centres in clusters is essential for efficient interaction.

Present work reports multiple ionization and subsequent Coulomb explosion of tetramethyl tin clusters induced by gigawatt intensity laser pulses. The time-of-flight mass spectra and charge density measurements revealed that the efficiency of laser–cluster interaction depends on ionization wavelength. Extent of energy absorbed from optical pulses by the cluster medium was found to increase with laser wavelength. Experimental results obtained in the present study have been rationalized on the basis of three stage cluster ionization model, i.e. multiphoton ionization ignited – inverse bremsstrahlung heating (IBS) – electron ionization. In addition to the experiments, theoretical calculations have been performed to account for screening effects in clusters. Our calculations suggest that the charged particles, generated upon initial multiphoton ionization of cluster constituents, significantly lower the Coulombic barrier of atoms/molecules that are present in its vicinity. This, in turn, decreases the ionization energy of cluster constituents, during subsequent steps of ionization, ultimately increasing the ionization level of clusters via the process of enhanced ionization due to ion shielding. Thus, above calculations predict dominant role of screening effects in evolution of higher charge state atomic ions during laser–cluster interaction.

Figure optionsDownload high-quality image (199 K)Download as PowerPoint slide