Ablation of insulators under the action of short pulses of X-ray plasma lasers and free-electron lasers

An experimental and theoretical study has been carried out of the ablation of a solid insulator with a wide band gap (LiF) under the action of ultrashort laser pulses of the UV range, obtained in a free-electron laser (pulse width τ L =0.3ps, photon energy ħω L =20.2eV), and the soft X-ray region, obtained in a silver-plasma laser (τ L =7ps, ħω L =89.3eV). A comparison is made of the results obtained on the two laser systems. It is shown that the ablation threshold is about the same for both lasers. A theory is presented that explains the weak growth of the ablation mass with increasing surface energy density of the laser radiation (the fluence) in the case of X-ray lasers as a result of the transition from spallation close to the ablation threshold to evaporative ablation at high fluence values.