The He-Ne laser is constructed from a tube containing a mixture of the two gases, with about a 1:10 ratio of neon to helium. The neon and helium atoms are shown as green and blue dots, respectively. The mirror at one end is totally reflective, while the one at the opposite end is about 99% reflective. The physical parameters are arranged so that the strongest laser emission is a beam of red light with wavelength 632.8 nm. In the principal mode of laser action, helium atoms are excited to their state by a high-voltage electrical discharge, and these collide with neon atoms, exciting an electron to a level. This produces a population inversion in the Ne atoms, and stimulated emission occurs when the excited electron makes a transition back to a level in its ground state.