What is the correct size of the pinhole?
You can calculate this (assuming you know all distances and radii in your resonator) using the complex ABCD formalism (see: “Lasers” by Anthony E. Siegman, University Science Books, May 1986, ISBN: 0-935-70211-3); there is a commercial software called PARAXIA, which can help you doing so. But in most cases it is easier simply to try different apertures and to find the best one iteratively. • Where is the best place for it? Again, you can calculate it (this may be necessary when you have a strong thermal lens); typically the best place is a waist of the beam. If you have a flat output coupler or end mirror, you will have a waist on the flat mirror; place the pinhole near this mirror. In other cases simply try different positions (perhaps you can guess the position of a waist).
You can calculate this (assuming you know all distances and radii in your resonator) using the complex ABCD formalism (see: “Lasers” by Anthony E. Siegman, University Science Books, May 1986, ISBN: 0-935-70211-3); there is a commercial software called PARAXIA, which can help you doing so. But in most cases it is easier simply to try different apertures and to find the best one iteratively. • Where is the best place for it? Again, you can calculate it (this may be necessary when you have a strong thermal lens); typically the best place is a waist of the beam. If you have a flat output coupler or end mirror, you will have a waist on the flat mirror; place the pinhole near this mirror. In other cases simply try different positions (perhaps you can guess the position of a waist).
