Experimental investigation of the spatial structure of the beam profile of a laser with a Sagnac interferometer

An experimental investigation was made of the spatial structure of the output beam profile of an Nd³⁺:YAG laser with a cavity based on a Sagnac interferometer. In a wide range of pulse repetition frequencies, the output beam profile could be described by a Gaussian curve with a confidence probability of at least 99%. This corresponded to the emission of the TEM₀₀ mode from a stable cavity. The diameter of the radiation spot was inversely proportional to the shift of a thermo-optical lens from the centre of the Sagnac interferometer.