Ablation mechanism of silica glass induced by laser plasma soft x-rays

We have investigated ablation of silica glass induced by laser plasma soft X-ray irradiation and demonstrated nano- and micromachining of silica glass using soft X-rays. To clarify the ablation mechanism, we observed ions ejected from the silica surface and found that 0.7% of the emitted species are ions and that a mean velocity is 9.8 x 105 cm/s. The kinetic energies of ions reached 25 eV, which is much higher than thermally evaporated atoms. These results revealed that ions are decomposed to atomic species and small molecules. The electrostatic energy of ions generated on X-ray irradiated silica surface is estimated to be 193 kJ/cm3. The energy density is comparable with the sum of the binding energy of silica glass (76 kJ/cm3) and the total kinetic energies of ablated species (90 kJ/cm3), which possibly results in ablation by the repulsive force. (author)