A laser machine emits energy in the form of heat and light that targets and heats up your hair follicle. The light is attracted to and absorbed by melanin, and the heat then travels down the base of the hair to the root where it destroys the interconnections that connect the hair root to the blood supply that nourishes it. Once these cells are completely destroyed, new hair can’t grow! (Pretty cool if ya ask me.)
A person with darker skin will typically need more sessions than someone with a paler skin as there is not as much direct intense heat going into each follicle, the energy is filtered in slower so as not to disturb the pigment in the skin.