LASER BEAM CRITICAL BEHAVIOUR AND PHASE CONJUGATION IN THE SEMICONDUCTORS, RESONANT MEDIA AND ELECTROOPTIC CRYSTALS N. Kukhtarev, A. Borshch, M. Brodin, V. Volkov and T. Semenets J. Phys. Colloques, 44 C2 (1983) C2-5-C2-14 DOI: 10.1051/jphyscol:1983202