Photoinduced electronic structure and nonlinear susceptibilities in Y-Ba-Cu-O ceramics

Photoinduced second harmonic generation in Y-Ba-Cu-O ceramics was investiga ted. An analysis of the observed effect was performed based on quantum chem ical modeling taking account of electron-phonon anharmonic interactions. Us ing band energy structure, calculations we have revealed a correlation betw een photoinduced electron charge density redistribution within the Cu-O oct ahedra of the Y-Ba-Cu-O ceramic and appropriate second-order nonlinear opti cal susceptibilities. Other structural fragments play only a minor role in the observed photostructural changes. The possibility of using the photoind uced optical second harmonic generation for detection of superconducting ph ase transition is demonstrated. (C) 2001 Elsevier Science Ltd. All rights r eserved.