Dynamic Acceleration Effects in Explosions of Laser-Irradiated Heteronuclear Clusters

Intense, femtosecond irradiation of atomic and molecular clusters can initiate Coulomb explosions, generating particle energies sufficient to drive nuclear fusion. Last and Jortner have proposed, based on particle dynamics simulations, that heteronuclear clusters with a mixture of heavy and light ions will not explode by the simple, equilibrium Coulomb model but that dynamic effects can lead to a boosting of energy of the lighter ejected ions [Phys. Rev. Lett. 87, 033401 (2001)]. We present experimental confirmation of this theoretically predicted ion energy enhancement in methane clusters.

Figure 1

Averaged energy spectrum and time of flight trace (inset) from ${\mathrm{CD}}_4$ clusters irradiated at $2.1\times {10}^{17}\mathrm{W}/{\mathrm{cm}}^2$.

Figure 2

Energy spectra from ${\mathrm{CH}}_4$ and ${\mathrm{CD}}_4$ clusters at a laser intensity of (a) $1.2\times {10}^{17}\mathrm{W}/{\mathrm{cm}}^2$ and (b) $3.2\times {10}^{17}\mathrm{W}/{\mathrm{cm}}^2$. Dotted lines indicate $E_{\min }$, above which signals are assumed to be solely due to the light ion species.

Figure 3

Simulated energy distribution for ${\mathrm{H}}^{+}$ (dotted line) and ${\mathrm{D}}^{+}$ (solid line) from the Coulomb explosion of a $({\mathrm{C}}^{4+}A_4{}^{+}{)}_{2109}$ cluster. Inset: Theoretical energy distribution from a homonuclear Coulomb explosion.

Figure 4

Simulated mean and maximum ion energies from the Coulomb explosion of a $({\mathrm{C}}^{4+}A_4{}^{+}{)}_{2109}$ cluster. Circles and triangles denote mean and maximum energies, respectively, from ${\mathrm{CH}}_4$, ${\mathrm{H}}^{+}$ in (a) and ${\mathrm{C}}^{4+}$ in (b). Diamonds and squares show mean and maximum energies, respectively, from ${\mathrm{CD}}_4$, ${\mathrm{D}}^{+}$ in (a) and ${\mathrm{C}}^{4+}$ in (b). The solid symbols represent the equivalent values from the simulations in Ref. 12.