The heat contribution of single electrons is very small, but the electrons can be accelerated by very high voltages, and by increasing their number (the beam current) the power of the beam can be increased to any desired value. By focusing the beam onto a small diameter on the surface of a solid object, values of planar power density as high as 104 up to 107 W/mm2 can be reached. Because electrons transfer their energy into heat in a very thin layer of the solid, as explained above, the power density in this volume can be extremely high. The volume density of power in the small volume in which the kinetic energy of the electrons is transformed into heat can reach values of the order 105 – 107 W/mm3. Consequently, the temperature in this volume increases extremely rapidly, by 108 – 109 K/s.