Cooperative effects in sonoluminescence

Atomic emission lines arising from caviation of sodium chloride and potassi um chloride aqueous solutions have been studied over a range of acoustic po wers and concentrations. Experimental observations of singular threshold be havior in multibubble, sonoluminescence are presented. It is shown that thr eshold type dependencies of peak width and intensity of the emission lines are consistent with the concept of the cooperative, many-body character of sonoluminescence. Our results strongly suggest that sonoluminescence may ha ve been the first experimentally observed collective optical emission effec t, almost three decades prior to the first realization of an optical laser. (C) 2001 Elsevier Science B.V. All rights reserved.