Cooperative emission of dye molecules at high dephasing rates

The dependence of the emission of a concentrated (～10¹⁹ cm^?3 solution of Rhodamine C on the power density Φ of exciting laser radiation was studied. The emission intensity for the power density of exciting radiation above ～10²⁵ cm^?2 s^?1 was found to have a nearly quadratic dependence on the power density Φ, and this emission was interpreted as the cooperative spontaneous emission of a Dicke type. For Φ?10²⁵ cm^?2 s^?1, the emission intensity increased with increasing Φ according to the exponential law. This emission was interpreted as the amplified spontaneous emission. The spectra of cooperative emission depended on the pump radiation power only weakly. The absence of lasing in dye solutions at high concentrations, which is a well-known phenomenon, was shown to be caused by the development of the cooperative spontaneous emission and not by the concentration quenching, and the former process is more rapid than the latter.