Investigation of the transverse structure of the radiation field of an injection laser using an external dispersive resonator

A method involving spectral selection of transverse modes with the aid of an external dispersive resonator was proposed and used to analyze the transverse structure of the radiation field of an injection laser. The spectral selection made it possible to excite consecutively several transverse modes. The efficiency and lasing threshold increased on increase in the index of the excited transverse mode. When the output flux density on the mirror of a diode was less than 0.6 mW/μm, free lasing was characterized by a superposition of these modes. A further increase in the power deformed the profiles of each of the modes and the structure of the field under free-running conditions was determined by an optical nonlinearity.