Enhanced explosion of atomic clusters irradiated by a sequence of two high-intensity laser pulses

Experiment and numerical simulations have shown that the heating of atomic clusters can be enhanced by using a correctly timed sequence of two high-intensity pulses of different frequencies. We have measured ion energies from Xe clusters irradiated with two high-intensity femtosecond laser pulses, one at the laser fundamental frequency (780 nm) and one at its second harmonic (390 nm), focused to an intensity of ~10¹⁵ W cm^-2. The ion energies are found to depend on the relative delay of the two pulses but not on their relative polarizations. For the optimum value of the delay between the two laser pulses, the maximum ion energy is doubled from 100 to 200 keV. The laser energy required to obtain a given ion energy is significantly less when the cluster is irradiated with two pulses of different frequencies than a single laser pulse.