What is optical confinement? What is it intuitively? How does this 'optical confinement' affect the performance of a laser?
Confinement is a property of a waveguide structure. It describes how large/wide in space the light mode is (or where the light is confined).
It affects laser performance because the active medium may be much thinner that the light mode and since the overlap of light mode and active medium gives the modal gain, having a good confinement (high modal gain) is crucial for good laser performance.
"What is it intuitively?" Here's what I visualize for this. If you had a small pool of water with regular waves in it and a bunch of rubber ducks on it, some ducks would be pushed up and down, others (where all the waves seem to cancel out) appear to sit and do nothing. Confinement is areas where nothing much happens and particles end up there.
Concerning laser performance, a light beam can only achieve confinement if its photons are all in phase. Too far away and the photons start to look a little out of phase, so a laser to be able to achieve 'optical confinement' of something, suggests its a pretty good laser.