Studying what a laser is is like reviewing humanity’s advances in the knowledge of natural phenomena over the last 200 years.
The laser is an achievement in human manipulation of the electromagnetic force.
Electromagnetic forces prevent gravity from taking us to the center of the Earth. They are manifested in the electrical charges that define each object: equal charges repel each other, different charges attract each other, and things we can touch are balanced.
When the balance of charges in a body is lost, electrons go to the place where there are fewer and we will have electrical manifestations such as lightning and sparks. By convention, we call positive charge when there is a defect of electrons and negative when there is an excess of electrons. The charges generate spaces around them with electromagnetic activity that we call fields, which when they come into contact with each other, collide and generate waves in space. The spectrum of waves that we manipulate is between radio waves of several meters up to gamma rays. Electromagnetic forces do not act within the nucleus of the atom, there other forces govern , some that overcome the electrical repulsion between protons and other forces that have mass and have their own field (Hicks).
Maxwell conceptualized electromagnetism as the result of the movement of charge fields, and he also predicted that waves traveled at the speed of light.
Man then had the need to find out how far and how long a light wave would travel and it was necessary to arrive at an abstract concept, the energy, the vital force that made a wave move against a medium occupied by many fields.
Einstein formulated the theory of relativity to explain the motion of matter and its relationship with the electromagnetic force. He applied the mechanical laws to electromagnetic waves, considering the speed of light as the maximum possible in an ideal medium, without interference and according to the time for the observer of the measurement. The inclusion of events in the formulas placed the variable of the speed of light with a stable value and thus made possible experiments with comparable values.
That energy was conserved was understood from mechanics, observing that something that was capable of producing movement would expend a force equivalent to that which it generated. Galileo had already found a constant not related to mass in his studies on the fall of objects and Leibniz took this with his approach to the vis viva, “living force”, with an equation that related energy equal to its mass times its speed squared, Descartes did not raise it to the square. Time was already being talked about, when considering speed, but there was no reference value that included it. Einstein changed the concept to time relative to the observer .
Planck had established that the way in which energy and matter interrelated was related to a constant that appeared to be the only way to explain that energy jumped in levels according to the frequency of the waves, to explain the change in the color of the light emitted by a metal at different temperatures.
Einstein postulated photons, light-carrying corpuscles without mass.
Einstein explained Hertz’s findings in relation to the photoelectric phenomenon. Hertz had observed that the addition of ultraviolet light to an electrical stimulus produced light from a metal immediately. Einstein, based on the constant postulated by Planck, proposed that for energy to be conserved, the energy with which electrons are expelled from the metal would have to be equal to the energy provided by the arriving photons, minus the energy needed to extract a single electron from the material. In other words, the light obtained depends on the energy according to the frequency of the incident wave. Both values were thus measurable and in 1916 Millikan verified the value of Planck’s constant, thus defining that the energy values change according to the frequency of the wave in energy jumps.
The model of the atom that was conceived when Einstein formulated the theory of relativity was that of a pudding with raisins. The electrons were the raisins with a negative charge, the nucleus had not been discovered, it was part of the pudding with a positive charge. The atom remained in equilibrium in terms of the number of its charges. Once the nucleus was discovered, Rutherford led us to a planetary model to which Bohr assigned energy levels, but above all, there were energy thresholds to make the electron change energy levels and as long as it maintained this level, it was stable and therefore its tendency was to return to its level, releasing the energy gained by emitting light. Bohr’s model explained well the recently discovered spectroscopy of the hydrogen atom, but it created the difficulty of associating the charge and position of an electron; the charge could be measured but the electron did not appear.
The simple planetary model became a cloud where the position of the electron at a given time was unknown. Louis de Broglie appeared and proposed an example of symmetry to relate masses and waves. The double nature of subatomic particles, both wave-like and at high speeds, also having a corpuscular behavior, led to the conception that electrons traveled as waves and arrived as particles. De Broglie had worked with stationary waves that are like those of guitars, where the notes change according to whole numbers and he associated this with the quantum levels of the Bohr atom, explaining its stability because, as stationary waves do not emit energy, they maintain it and the frequency of the wave would be related to a constant, the mass and speed of the electron. An intermediate explanation to give stability to the Bohr model that was the basis for finding the electron.
Schrödinger translated Broglie’s formulation into terms of probabilities, to situate the electron wave and forcing us to change the interpretation that we would have to make of these probabilistic waves, equal to the others but reconstructed in little pieces. And although, when we do not know something we resort to probability, it is true that when we have almost all the information in the same system, this increases to 100% certainty. The wavelength was then related, in probabilities, to a constant divided by the mass and its speed so that we could see the subatomic structures, it was thus possible to manipulate electrons by increasing their speed with magnetic forces, to obtain increasingly smaller waves and thus we arrived at the electron microscope and all the other systems for generating protons and neutrons.
Einstein invents the laser
Einstein himself was able to explain the sustained equilibrium of a light emission based on the presence of a repetition of stimuli that would multiply photons, in what he described as stimulated emission. An electron would rise to a higher energy level when it gained enough energy and release it to return to its basic level, but if it is excited before decaying, a multiplication phenomenon would occur, since the electron would still decay but release two photons. It does not gain another level. His equation for a laser, the possibility of obtaining a purer and more powerful light, became a reality with Theodore Maiman in 1960, five years after Einstein’s death.
