We had made progress in Livermore in many different fields, not all of them connected with nuclear explosions. One active field which remains very active to this day is connected with the development and the use of lasers. Perhaps the idea of lasers is not yet quite generally known, so let me explain the concept in a few words. The usual behavior of light as it goes through material is absorption and absorption proceeds in an exponential fashion, such that in a certain thickness half of the light will be absorbed and only half is left over. You add that distance once again and only one quarter will be left over, and once again and only one eighth, and ten times the distance and one tenth of 1% of the light remains. Now this process of absorption is due to a transition of atomic structures from a lower state to a higher state where in the natural presence of a material, practically all the particles are in the lower state, and their systematic absorption of light gives rise to this exponential decrease of the radiation that can get through. The idea and the practice of the lasers is, by a number of various often not simple means, to create a temporary situation where, for instance in a gas, more molecules will be in the upper state than in the lower state. Then the opposite of absorption will happen. It turns out that the idea goes back to Einstein, that in addition to a possibility absorption, where an atomic system goes from a lower state to an upper state, and the relevant energy is then subtracted from the energy of radiation that caused the transition, Einstein proposed that the opposite process should also exist and was indeed found to exist. If you manage to produce a great number of atoms with the majority in the upper state, then when light goes through, after a certain distance enough of the atoms which ha- will have delivered their energy to the light so that the intensity of the light is doubled. And you repeated that ten times and you have increased the intensity of light tenfold. This is a development that had been foreseen for a number of years but became a reality a third of a century ago and the result is that we can now produce very energetic, very precisely directed beams of light, and these are the lasers.
