Time-resolved spatial profile of TEA CO2 laser pulses: influence of the gas mixture and intracavity apertures.

The evolution of the intensity profile of transversely excited atmospheric CO2 laser pulses is investigated within the intensity moment formalism. The beam quality factor M2 is used to study the mode evolution. Attention is focused on the influence of both the gas mixture (N2 :CO2 :He) and the diameter of an intracavity diaphragm placed to attenuate higher-order modes. The degree of accuracy that can be attained by approximating the laser field amplitude by means of the lower-order terms of a Hermite-Gauss expansion is also analyzed. In particular, a bound for the truncation error is given in terms of two time-resolved spatial parameters, namely the beam width and the M2 parameter.