The use of laser technology in the manufacturing processes of mechanical engineering is gradually increasing. However, laser welding cannot compete with electron beam welding because the processes of the interaction of the laser beam with the plasma arising above the zone of the laser beam affecting the metal are not sufficiently studied. Of particular interest is the use of laser welding in vacuum. The study of the secondary emission signal in the zone of the laser beam affecting the metal allows one to obtain information about the plasma cloud in the zone of laser welding in vacuum. To study the secondary emission current in the laser welding zone, a computer system with an analog-to-digital interface can be used. The registered secondary emission current made it possible to estimate such parameters of the plasma arising in the laser welding zone in vacuum as the plasma concentration, electron temperature, and plasma potential.