The influence of diffusion upon the amlification of a Gaussian laser beam in a CO2laser amplifier

Gain saturation for filamentary parts of a Gaussian laser beam were measured in a CO2laser amplifier using a pinhole technique. The results show that the detailed growth of a Gaussian beam in the amplifier as well as the overall growth can be described by the well-known homogeneous saturation function. The small-signal gain constant was found to have the same value of 2 dB/m for all radial positions on the beam. The saturation parameter, however, decreased from a maximum Value of 40 W/cm²on the beam axis to 18 W/cm²on the beam wings. The profile of the saturation parameter had an approximately Gaussian shape with a width of 3.9 mm, the same as the width of the laser beam. Diffusion is suggested as the reason for this radial variation of saturation characteristics.