OUTPUT  CHARACTERISTICS

     In an argon laser (the most popular ion laser), the powerful blue line at 488 nm appears first as current through the discharge is gradually increased, followed by other visible lines. Ultimately, the output power available on the 514-nm green line exceeds that of the blue line, despite the fact that the blue line has the highest gain in this system (almost an order of magnitude greater than any other transition). The quantum processes governing a multiline laser are anything but straightforward.

     When operated at high power levels, argon lasers tend to operate in multiple transverse modes. In many cases the TEM₀₁ donut mode is favored (probably because the bore is relatively small and hence cannot support particularly high orders). With the aperture installed, the laser can easily be made to oscillate strictly in TEM₀₀ mode, giving excellent beam quality. Also, most ion lasers (those with Brewster windows) have highly polarized outputs. Given the high operating temperatures of an ion laser plasma, the spectral width of these lasers is relatively large compared with that of other types. As we calculated earlier, argon lasers frequently exhibit a width of 5 GHz. This, of course, can be reduced through the use of intracavity etalons, allowing single-mode operation with an extremely narrow linewidth of only 1 to 2 MHz.