They have a material that supplies electrons and a power source that lifts the energy level of those electrons.

VOA: special.2010.09.01

Victor Weisskopf's suggestion resulted in an explanation of how electrons travel through semiconductors.

VOA: special.2010.11.09

In Theodore Maiman's first laser, a rod of man-made ruby supplied the electrons.

VOA: special.2010.09.01

And it was proposed by my thesis advisor Professor Weisskopf that we work on this problem to understand the effect of the impurities in scattering electrons and interfering with their motion.

VOA: special.2010.11.09