From numerical calculation,the basic rules of saturated gain coefficient variation with the field distribution along the flow direction in a GDL cavity are presented.In connection with variations of vibrational energy and temperature of all modes,these rules are explained with the physical mechanism of relaxation of the active medium.It is pointed out that,for example,there still-exists considerable vibrational energy which can be used for Gerry’s device with 30 KW monomode output.