Tube and mirror adjustments interact with one another, so you will probably find it necessary to repeat the sequences several times, first walking the mirrors, then moving the tube, then walking the mirrors again, .  . . After several iterations you will reach a point where the last possible milliwatt has been coaxed from the laser.

Some laser models (ie: Coherent ) have a movable aperture. In cases such as these the alignment of the tube to aperture is not as critical. Centering the tube on the front and rear optics is sufficient. Once this is achieved these "movable apertures" can be brought into alignment usually by a set of positioning screws located by the aperture assembly. A common "low power" situation is when the laser beam is being clipped by the aperture, not allowing full use of the plasma tube bore.

This sequence insures that the beam will travel directly through the center of the aperture, which is mounted between the plasma tube and the output coupler. It is different from the factory alignment procedure, which requires special fixtures and tools that keep the beam in the center of the high reflector as well. Since it does not insure precise centering on the high reflector, the interchangeability of single-line prisms may suffer. You may also notice a slight overall power loss.

Clean the plasma tube windows; an acetone wipe which should be sufficient (see "Cleaning Plasma Tube Windows" for details).

Because thermal effects in intracavity spaces affect the beam, this final cavity alignment sequence should be done with the cavity in its operating condition. Before you install the cavity seals, however, check the position of the beam as it enters the high reflector mirror mount. It should be as close to the center of the opening as possible. Verify that the purge system is turned on.