On obtaining well defined transverse modes and selective line tuning of a long CW CO2laser

It is found that a long conventional CW CO 2 laser cannot be tuned selectively because of the multidirectional modes formed through reflections at grazing angles from the inner walls of the discharge tubes. This problem has been overcome by inserting a number of properly designed mode-selecting apertures right into the discharge tubes and selective tuning over more than 150 rotational lines in both P and R branches of three vibrational bands (9.6, 10.6 and 11.2 mu m) has been achieved. The rotational lines of higher J-values that have a low gain tend to lase in the TEM 10 mode. In the R branch two consecutive lines are observed to lase simultaneously when the angular width of the active medium subtended at the grating allows the existence of two physically tilted beams of different wavelengths dispersed by the grating used. The output power distribution over various lines almost follows that of the gain. The optimum design parameters of a long CW CO 2 laser for tuning are obtained.