Dye-laser threshold in a protein solution

We propose to study the cooperative effects in a system exhibiting a phase transition by measuring the temperature dependence of the threshold pumping power required for laser oscillation from organic dyes in the sample. In the present experiments, we have chosen a protein (lysozyme) as the substance with a phase transition. Comparing measurements of optical absorption, fluorescence and optical rotation spectra, we found two types of temperature-dependent phase transition in lysozyme. The role of the coherent intermolecular interaction is discussed.