Non-stationary structural changes in HTS composites under the influence of high intensity femtosecond laser pulses

The paper presents the results of experimental study and numerical analysis of defect formation processes in superconducting YBa2Cu3O7-x films on Hastelloy substrate under the influence of ultrashort laser radiation. The aim of the work is to develop a technique for numerical analysis and calibration of modes of exposure to high intensity femtosecond laser pulses to create systems of controlled defects in HTS composites. The processes of defect formation under the influence from 1 (single mode) to 20 (multiple mode) laser pulses on one point with a frequency of 10 Hz and duration of 2 ps were considered. The laser beam focusing radii were 1.5 and 3 μm. The dependences of the defect diameter and depth on the laser radiation energy in a wide range have been studied and the peculiarities of defect formation in the multiple mode have been shown. The physical processes occurring under the influence of laser radiation in different focusing modes are demonstrated. The proposed technique in the future can be extended for application in experiments of electron-probe spectroscopy, which will make it possible to study changes in the state of the electron-phonon subsystem of superconductors up to phase transitions associated with melting of the crystal lattice.