By taking the integrated intensity profiles in a number of cuts, the original beam profile can be reconstructed using algorithms developed for tomography.
Measuring the far-field beam profile directly is often impossible in a laboratory because of the long path length required.
A low M only implies that the second moment of the beam profile expands slowly.
A second pair of (spherical) lenses image this square beam profile inside the laser crystal.
The latter statements also hold true for a Gaussian beam profile, as a numerical integration shows.
This needs to be considered if a good beam profile is to be achieved in laser applications.
Line-collimation instruments confine the beam only in one dimension so that the beam profile is a long but narrow line.
Pumping with a single lamp tends to focus most of the energy on one side, worsening the beam profile.
Other common beam profiles are the C-channel, the hollow structural section beam, the pipe, and the angle.
Out of plane resonators lead to rotation of the beam profile and more stability.