So you end up with a heap of identical photons in terms of energy and phase. The gas tube has a mirror at each end which reflect the emitted photons back into the tube for further collision, but only photons travelling exactly parallel to the tube are reflected by the mirror, others just escape. In addition, one of the mirrors is only partially reflective, it also lets some of the photons travelling parallel to the tube through. Thus out of one end of the laser a stream of parallel, identical photons is emitted - and this is what a laser is. In addition to gas lasers there are dye lasers which use a liquid coloured by a dye, semiconductor laser chips made from semiconductors, solid state lasers made from rods of solid, transparent materials, and chemical lasers.
Semiconductor lasers are the smallest and can now be made as small as a pin head.